Field Guide to the Reptiles of the Northern Territory 1486312683, 9781486312689

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FIELD GUIDE TO THE REPTILES OF THE NORTHERN TERRITORY CHRIS JOLLY, BRENDAN SCHEMBRI AND STEWART MACDONALD

FIELD GUIDE TO THE REPTILES OF THE NORTHERN TERRITORY CHRIS JOLLY, BRENDAN SCHEMBRI AND STEWART MACDONALD

© Chris Jolly, Brendan Schembri and Stewart Macdonald 2023 All rights reserved. Except under the conditions described in the ­Australian Copyright Act 1968 and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, duplicating or otherwise, without the prior permission of the copyright owner. Contact CSIRO Publishing for all permission requests. Chris Jolly, Brendan Schembri and Stewart Macdonald assert their right to be known as the authors of this work. A catalogue record for this book is available from the National Library of ­Australia. ISBN: 9781486312689 (pbk) ISBN: 9781486312696 (epdf) ISBN: 9781486312702 (epub) How to cite: Jolly C, Schembri B, Macdonald S (2023) Field Guide to the Reptiles of the Northern Territory. CSIRO Publishing, Melbourne. Published by: CSIRO Publishing Private Bag 10 Clayton South VIC 3169 Australia Telephone: +61 3 9545 8400 Email: [email protected] Website: www.publish.csiro.au Sign up to our email alerts: publish.csiro.au/ earlyalert Front cover: (top) Oenpelli python/nawaran (Nyctophilopython oenpelliensis) (photo by Chris Jolly); (bottom, left to right) thorny devil (Moloch horridus), northern knob-tailed gecko (Nephrurus sheai), spotted tree monitor (Varanus scalaris) (photos by Brendan Schembri) Back cover: (left to right) crack-dwelling whipsnake (Demansia rimicola), Cann’s long-necked turtle (Chelodina canni), blue-tailed finesnout ctenotus (Ctenotus calurus) (photos by Brendan Schembri)

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Edited by Joy Window Cover design by Cath Pirret Typeset by Envisage Information Technology Printed in China by 1010 Printing I­nternational Ltd CSIRO Publishing publishes and distributes scientific, technical and health science books, magazines and journals from A ­ ustralia to a worldwide audience and conducts these activities autonomously from the research activities of the Commonwealth Scientific and Industrial Research Organisation (CSIRO). The views expressed in this publication are those of the author(s) and do not necessarily represent those of, and should not be attributed to, the publisher or CSIRO. The copyright owner shall not be liable for technical or other errors or omissions contained herein. The reader/user accepts all risks and responsibility for losses, damages, costs and other consequences resulting directly or indirectly from using this information. CSIRO acknowledges the Traditional Owners of the lands that we live and work on across ­Australia and pays its respect to Elders past and present. CSIRO recognises that Aboriginal and Torres Strait Islander peoples have made and will continue to make extraordinary contributions to all aspects of ­Australian life including culture, economy and science. CSIRO is committed to reconciliation and demonstrating respect for Indigenous knowledge and science. The use of Western science in this publication should not be interpreted as diminishing the knowledge of plants, animals and environment from Indigenous ecological knowledge systems. The paper this book is printed on is in accordance with the standards of the Forest Stewardship Council® and other controlled material. The FSC ® promotes environmentally responsible, socially beneficial and economically viable management of the world’s forests.

Foreword Australia’s Northern Territory is a land of diverse habitats. In land area it totals about 20% of the Australian continent, but houses only 1% of its human population. The Northern Territory does, however, support an assemblage of about 400 reptile species and is a paradise for herpetologists and reptile enthusiasts. During 40 years of studying reptiles and their taxonomic relationships in the ­Northern Territory, my research was often complicated by the lack of a single guide to the identification of Northern Territory species. Accurate identification of specimens generally required the use of guides to all Australian reptiles, thus including a multitude of superfluous and confusing species. In many cases, identification also required reference to bulky reams of scientific literature. In an attempt to partially fill this need for local field guides, I authored Skinks of the Northern Territory which was published in 1991. Aside from only documenting one reptile family, that guide is now considerably dated in respect to recently described species, as well as modern taxonomy and nomenclature. Finally, for the first time, Field Guide to the Reptiles of the Northern Territory presents and illustrates all reptiles currently recorded from the Northern Territory in a single volume. Individually and collectively, authors Chris, Brendan and Stewart have brought a wealth of expertise and knowledge to the writing of this book.

In combination, their experience has resulted in a text that is concise, accurate and informative. The information presented is beautifully complemented by outstanding photographic skills and drawings, which clearly illustrate important features such as intraspecific variation and key attributes needed for identification. Another important feature is the accurate dichotomous keys to genera and species. Their inclusion allows the reader to readily check the identification of specimens and, used in combination with the accurate distribution maps, greatly assists in avoiding confusion between superficially similar species. Formatted in a user-friendly way and field companion size, Field Guide to the Reptiles of the Northern Territory will not only appeal to those specifically interested in herpetology, but will prove to be valuable and extremely useful to all readers. With its publication, the public is now given the means to accurately identify Northern Territory reptile fauna and, thus, has the opportunity to contribute to the documentation, protection and conservation of the Territory’s biodiversity. Paul Horner, PhD Emeritus Curator of Terrestrial Vertebrates Museum and Art Gallery of the Northern Territory August 2021

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Contents Foreword iii Acknowledgementsv Prefaceviii Introductionxv

1. Crocodilians1 2. Turtles and tortoises Sea turtles Leatherback turtle Side-necked turtles Pig-nosed turtle

4

6 13 14 25

3. Lizards27

Southern padless geckos 31 Austral geckos 36 Typical geckos 71 Legless lizards 93 Skinks106 Dragons213 Monitors250

4. Snakes269

Blind snakes 272 Pythons283 File snakes 292 Colubrids294 Homalopsids300 Terrestrial elapids 306 Marine elapids 349



iv

Venom, snakebite and first aid Glossary and abbreviations References and suggested reading Index of common names Index of scientific names

371 374 378 384 390

Acknowledgements First, we all owe a huge debt of gratitude to the support, encouragement, assistance and tolerance afforded to us by our respective partners and families. All of these wonderful people have (mostly) tolerated (sometimes begrudgingly) our life-long herpetological obsessions  – obsessions that often impinged on the trajectory of their own lives. Profound thanks are owed specifically to Alana de Laive and Natalie Schembri for accompanying us in the field, for enduring extended physical and metaphorical absences while we were in the field, glued to a computer screen or simply deep in thought about reptiles, for tolerating herp trips masquerading as holidays and for picking up the slack in everyday life while we doggedly pursued the accumulation of herpetological knowledge. We will be forever grateful and indebted to them. We also all owe a huge debt of gratitude to our respective families. We have all been extremely lucky to have had parents who, presumably against their better judgment and common sense, encouraged and supported our childhood passion for reptiles. A special thanks is also owed to the newest of our family members – Mala Juno Jolly. Without her birth and the resulting month of parental leave, this book may have never been completed. Many thousands of original photographs were made available to us for consideration for inclusion in this photographic field guide and we are grateful to the efforts of herpetological photographers across A ­ ustralia and abroad. For giving us access to their vast collections of photos we would like to

thank: Luke Allen, Paul Barden, Shane Black, Elliot Budd, John Cann, Sharee Carton, Matt Clancy, Hal Cogger, Henry Cook, Jordan de Jong, Alana de Laive, Alexander Dudley, Ryan Ellis, Jules Farquhar, Aaron Fenner, Ryan Ellis, Greg Fyfe, Nick Gale, Nic Gambold, Lachlan Gilding, Matt Greenlees, Greg Harold, Ryan Hart, Alex Holmes, Paul Horner, Grant Husband, Mark Hutchinson, Max Jackson, Angus Kennedy, Damian Lettoof, Etienne Littlefair, Ray Lloyd, Jacob Loyacano, Stephen Mahony, Brad Maryan, Peter McDonald, Ross McGibbon, Lindley McKay, Angus McNab, Jake Meney, Ian Morris, Eridani Mulder/AWC, Jordan Mulder, James Nankivell, Rex Neindorf, David Nelson, Tom Parkin, Arne Rassmussen, Wes Read, Mark Sanders, Ruchira Somaweera, Gary Stephenson, Matt Summerville, Dane Trembath, John Turnbull, Kanishka Ukuwela, Eric Vanderduys, Gary Vas, Nick Volpe, Brenton von Takach, Jordan Vos, MahreeDee White, Martin Whiting, Steve Wilson, John Wombey, Justin Wright, Christina Zdenek, Anders Zimny and Stephen Zozaya. We are grateful to Hal Cogger and CSIRO Publishing, who gave us permission to use part of their treasure trove of scientific illustrations. While we did many ourselves, we are also very grateful for Alana de Laive’s contribution to the illustrations in the book. We are extremely grateful to the experts who willingly devoted time to reviewing each chapter, including John Cann, Ryan Ellis, Paul Horner, Grant Husband, Mark Hutchinson, Etienne Littlefair, James Nankivell, Paul Oliver, v

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Tom Parkin, Octavio Jimenez Robles, Dane Trembath, Steve Wilson, John Woinarski and Stephen Zozaya. This book was motivated by an enormous number of devoted amateur and professional naturalists, ecologists and herpetologists across ­Australia who, until the publication of this book, lacked a specific, comprehensive field guide to the abundant, diverse and iconic reptiles of the Northern Territory. Without the support, assistance and encouragement of the mates with which we share a passion for reptiles, this book would not have been possible. For their friendship, companionship, mentorship and shared reptilian affliction, we thank Luke Allen, Paul Barden, Ian Brennan, Greg Brown, Neville Burns, Gordon Canning, Keith Christian, Matt Clancy, Hal Cogger, Henry Cook, Peter Cooper, Jenna Crowe-Riddell, Jordan de Jong, Sean Doody, Alexander Dudley, Damien Esquerré, Jules Farquhar, Aaron Fenner, Alaric Fisher, Nic Gambold, Lachlan Gilding, Graeme Gillespie, Matt Greenlees, Tony Griffiths, Jessica Harris, Ryan Hart, Brydie Hill, Paul Horner, Grant Husband, Naomi Indigo, Chris Jackson, Max Jackson, Tim Jackson, Damien Lettoof, Cara Littlefair, Dan Lynch, George Madani, Terry Mahney, Stephen Mahony, Phil Mangion, Brad Maryan, Peter McDonald, Angus McNab, Jane Melville, Jake Meney, John ‘Mango’ Moreen, Ian Morris, Cecilia Myers, Dale Nimmo, Paul Oliver, Chris Pavey, Magnus Peterson, Ben Phillips, David Rhind, Octavio Jimenez Robles, John Scanlon, Glenn Shea, Rick Shine, Adam Smart, Ruchira Somaweera, Alistair Stewart, Matt Summerville, Gerry Swan, Dane Trembath, James Van Dyke, Eric Vanderduys, Gary Vas, Nick Volpe, Georgia Ward-Fear, Jonathan Webb, Steve Wilson, David Wilson and Anders Zimny. Special thanks are owed to Alana de Laive, vi

Etienne Littlefair, Jordan Mulder, Tom Parkin, Brenton von Takach and Stephen Zozaya for their dedication to documenting the reptiles of the Northern Territory with us. Without them this project would’ve been far less productive and enjoyable. We are grateful to Graeme Gillespie, Eric Vanderduys and John Woinarski, who provided endorsements for the publication of this book. We are indebted to Brodie Kals for his expert graphic design of the initial proposal. We are very grateful to Paul Horner (‘Foreword’) and Tim Jackson (‘Venom, snakebite and first aid’) for their contributions to the book. We are very grateful to Gavin Dally, Michael Hammer, Sue Horner and Paul Horner of the Museum and Art Gallery of the Northern Territory, Tom Parkin, Jodi Rowley and Dane Trembath of the ­Australian Museum, and Paul Doughty of the Western A ­ustralian Museum for support and access to the collections. We thank the Atlas of Living A ­ ustralia and ­Australia’s many natural history museums for being invaluable repositories of information, without which this book would have been impossible. We thank the publishing team at CSIRO Publishing, who were always extremely attentive and encouraging and who tolerated numerous extensions of our submission date. In particular, we would like to thank Melinda Chandler, Mark Hamilton, Briana Melideo, Eloise Moir-Ford and Lauren Webb. We thank Joy Window for her careful copy editing of the book. There are a huge number of unnamed Territorians who assisted us, either intentionally or unintentionally (possibly begrudgingly), in our pursuit of reptiles of the Northern Territory – station managers that let us poke around their junk piles, members of the public who reported interesting reptile sightings, remote

Acknowledgements

roadhouses that stayed open later so we could refuel after road cruising, etc. – to you we owe an earnest debt of gratitude. We are also incredibly grateful to the Indigenous people  – the Traditional Owners  – of the country which we have here referred to as the Northern Territory. This book was predominantly researched and written on Larrakia country; however, we acknowledge the Indigenous people of

all Aboriginal nations across the Northern Territory and pay our respects to their Elders, past and present. We have been welcomed onto country by Aboriginal people throughout the Northern Territory and for that we are very grateful. In memory of Tim Schembri (1983– 2002), big brother, fellow reptile lover and someone who would’ve loved exploring for reptiles in the Northern Territory.

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Preface We created this Field Guide to the Reptiles of the Northern Territory to give users information about, and to aid in the identification of, the reptiles of the Northern Territory. We present introductions to each taxonomic grouping (e.g. order, family, genus); dichotomous keys to family, genus and species; and species profiles, including morphological descriptions, photos, distribution maps and notes regarding natural history. This book features profiles for the 390 species that are known to occur or may occur on the land and in the sea of the Northern Territory and its associated offshore islands as of June 2022. Due to the rapid rate of species descriptions and redescriptions, this book will undoubtedly be out of date by the time it reaches you. While the information is not exhaustive, we hope to provide sufficient information so that you can identify the reptile you are looking at in the field. Frustratingly, because some species are simply not reliably distinguishable based on morphological characteristics, accurate identification is not always possible. Where this is the case, we have highlighted which species may prove difficult to identify and why. The distribution maps will be helpful in many of these situations, but sometimes species may only be definitively identified by using genetics.

Taxonomic classification Humans love putting things into groups. It helps us bring order to the chaos of the world around us. In the 1700s, a Swedish botanist named Carl Linnaeus developed the system of classification that is, in essence, the same system in use today. viii

Building on the work of those who came before him, Linnaeus standardised the way we group organisms into a hierarchy of ranks. Taking the northern blue-tongue as an example, the major ranks are: Kingdom: Animalia Phylum: Vertebrata Class: Reptilia Order: Squamata Family: Scincidae Genus: Tiliqua Species: scincoides Subspecies: intermedia Of particular note is Linnaeus’s implementation of the binomial (‘two name’) system, involving a genus (Tiliqua) and a species (scincoides) name. The genus (plural: genera) name always starts with an uppercase letter, while the species name is in lowercase. Some species are further divided into subspecies, a rank typically used for geographically separated populations that may differ in small ways. Subspecies are represented by a third name (to make a trinomial system): Tiliqua scincoides intermedia. All three names are always italicised or underlined when written. This hierarchical and branching structure is often thought of as the Tree of Life, with the trunk and larger branches representing the higher level ranks and the smaller branches and leaves representing genera and species. The decision as to which branch these names are applied to is often arbitrary, giving rise to intermediate rankings, such as superfamilies, infraorders and subgenera. The ranks that are most relevant to this book are class (the book only deals with

Preface

class Reptilia), order, family (each chapter deals with a different reptile family), genus and species (within each family chapter, profiles are organised alphabetically by genus and species). Relevant subspecies are mentioned even if those subspecies don’t occur in the Northern Territory. Historically, organisms were grouped together based on shared traits (e.g. two animals that both give birth to live young were put in the same group). Nowadays, however, most scientists agree that species should be grouped based on a shared evolutionary history – two individuals that are closely related are classified as the same species; species that are each other’s closest relatives are put in the same genus. While closely related organisms will indeed share many traits, convergent evolution  – the process by which similar evolutionary pressures result in similar body forms or behaviours arising in otherwise unrelated species  – means that using morphology alone can result in inaccurate groupings. Recent advances in genetic analysis have allowed us to build much more accurate family trees of species. Instead of using only a handful of morphological characteristics, scientists can now use hundreds, or thousands, or tens of thousands of genetic characteristics to assess relatedness and determine what we should call a species and where on the Tree of Life that species should be placed.

What is a species? It’s very easy to define a species in theory (so easy, in fact, that there are numerous species definitions), but surprisingly hard to apply that definition in practice. One of the most popular concepts, the biological species concept, defines a species as a group of individuals that can freely breed with one another and produce fertile offspring – a simple concept that breaks down

when you try to use it. For example, it can only be applied to species that reproduce sexually  – it’s of no use for bacteria. Another popular definition views species as the end points on the Tree of Life. You can look at an individual, and all its children, and all its children’s children, and so on. Eventually, you will end up with a group (called a clade) comprised of an ancestral organism and all of its descendants. This definition fits nicely with our concept of the branching nature of life, but an arbitrary decision still needs to be made about how far back up the family tree to start the group. If you go back far enough, you’ll end up with everything on Earth classified as a single species. Despite the difficulties of creating and applying a useful definition, the species is the fundamental unit of taxonomy. In turn, species are used to measure conservation outcomes. We talk about population declines when individuals of a species die without replacing themselves. We talk about biodiversity loss when species go extinct. We talk about biodiversity hotspots in areas that have lots of species, especially if those species are found nowhere else. As such, being able to identify species is vital when documenting the planet’s biodiversity. We hope this guide will make that job easier for users in the Northern Territory, while simultaneously recognising that it can be hard or impossible to assign an individual to a species. This may be because individuals can exhibit variation not covered by a species definition or the profile in this guide. That variation might be genetic (a random mutation that might be passed on to any progeny) or it might be nongenetic (maybe the embryo experienced extreme temperatures while developing in its egg, which caused its scales to form differently). That variation might be a one-off situation, or it might be because the ix

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individual you found actually represents an undescribed species. This guide covers the known variation within each species. If you find a reptile in the Northern Territory that does not fit any of the descriptions within this guide, please let the Museum and Art Gallery of the Northern Territory (MAGNT) know and include as much information as possible, such as the date, location (use your phone’s GPS to get accurate coordinates), and photos of the animal (highlighting the features that are making identification tricky). Despite all this talk of variation, chances are that the majority of the reptiles you find in the Northern Territory will be known species and you’ll be able to confidently identify them.

Common names Common names are given to taxa to improve non-technical communication, but are non-standardised. For example, the tree snake species Dendrelaphis punctulatus has only one scientific name. However, this snake is known by several, regionally specific common names, such as A ­ ustralian tree snake, common tree snake, green tree snake and golden tree snake. In Sydney, this species is green in colour and is colloquially known as the ‘green tree snake’. In Darwin, this same species is golden–yellow in colour and is colloquially known as the ‘golden tree snake’. Although common names are not standardised in ­Australian reptiles, we have provided the most commonly used common name for each species, as well as some alternative names where they are in common usage in the Northern Territory. As a general rule, common names are not capitalised. However, any proper nouns (e.g. the names of people or places) in the name are capitalised (e.g. Cann’s longnecked turtle, Groote Eylandt dwarf blind snake). Following the rules of English x

grammar, the first word in a common name is also capitalised if it appears at the start of a sentence.

Scientific names It’s often said that scientific names are better than common names because a species only ever has one scientific name that never changes, and everyone knows to use that name. This, however, is not true. Scientific names often change more than common names do. This is because scientific names are tied to a species concept. The advantage of this is that a scientific name will immediately tell you something about the organism’s close relatives. Based on its scientific name, we can tell that the eastern brown snake (Pseudonaja textilis) is closely related to all the other species in the Pseudonaja genus. The downside of this system is that, as our understanding of how organisms are related to each other changes, so too can the names we call them. The great desert skink was originally described with the name Egernia kintorei, but recent work has shown that it’s more closely related to a group of burrowing skinks in the genus Liopholis, so it has been moved into that genus and had its name changed to Liopholis kintorei. While frustrating, name changes are the inevitable consequence of an increased understanding of the evolutionary histories of the organisms we apply them to. Name changes can also come about due to what is essentially the heavily opinionbased nature of taxonomy. Scientists have different opinions about what constitutes a species, as reflected in the multiple species definitions that are in use. Even when using one definition, scientists may differ in how they apply that concept. And even for a widely accepted species, people may argue about which name to use.

Preface

The International Commission on Zoological Nomenclature (ICZN) has developed a series of rules (‘The Code’) for how to name taxa and what constitutes a valid name. Typically, the first name given to a species has priority. When Eric Worrell described Varanus bulliwallah in 1956, he didn’t realise that Ludwig Glauert had already described the species in 1951. Given that Glauert’s description was published 5  years earlier, the name he used, Varanus mertensi, has priority and is the name we use today for Mertens’ water monitor. This concept even applies within the same publication or article, where the name that first appears, even if it’s misspelt, is the name that has priority. While we refer to them as rules, they act more like guidelines. When Gerard Krefft first described the freshwater crocodile and named it after the discoverer, Mr Robert Johnstone, he unfortunately misspelt the discoverer’s name as Mr Johnson and repeatedly referred to the new species as Crocodylus johnsoni. When he realised his mistake, Krefft acted to point out his error and the name was corrected to Crocodylus johnstoni. While johnsoni was published first and should therefore have priority, ‘The Code’ does have provisions for emending names where mistakes have been made. As such, the name Crocodylus johnstoni is generally accepted as the correct, valid name and is the name used by most publications today. The situation becomes murkier when names are published without adequate descriptions, because what constitutes an ‘adequate description’ is up for debate. Where multiple names are available for a species, we typically use the names recognised by the ­Australian Society of Herpetologists’ Official List of A ­ ustralian Species (2022) (available online at http://www. australiansocietyofherpetologists.org/ash-

official-list-of-australian-species). Ultimately, usage by the wider community will determine which names stick. As well as information on relationships, scientific names can give you other information about the animal: where it comes from (e.g. Rhynchoedura eyrensis, found in the Eyre Basin), who it was named after (e.g. Strophurus horneri, named after Dr Paul Horner of MAGNT), or what it looks like (e.g. the long-nosed dragon, Gowidon longirostris, named for its long rostrum). If you want to refer to a member of a genus without specifying the species (because you don’t know the species, or because you want to refer to multiple species), you can use the abbreviations ‘sp.’ (singular) and ‘spp.’ (plural). For example, if you can’t identify an animal to species, but you know it’s a dtella gecko, you could refer to it as Gehyra sp. (no need to italise the sp., but make sure you include the trailing full stop to show it’s an abbreviation). Alternatively, if you want to refer to multiple dtella geckos, you could talk about Gehyra spp. In fact, you might often refer to Gehyra sp. or Gehyra spp., because they are notoriously problematic to identify.

Identification Reptile identification can be tricky, even for experts. Some reptiles are easy to identify. For example, a 5 m crocodile observed on the Adelaide River is undoubtedly a saltwater crocodile (Crocodylus porosus) because no other species of crocodile grows this large in the Northern Territory. Most reptiles, however, are considerably smaller and require close examination to identify. Some reptiles are remarkably variable within a species, while others are extremely conservative within a genus. Sometimes, the arrangement or presence of a single scale can be the only means of differentiating xi

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two similar species. Increasingly, species are being identified via genetic differences and taxonomists struggle to find morphological features to readily distinguish closely related species from one another. With experience, however, many similar reptile species become easy to identify based on subtle differences in colour pattern, body proportions, behaviour and habitat associations. When using this guide to identify a reptile, the starting point will be the appropriate dichotomous key.

Dichotomous keys The dichotomous keys in this guide are like a ‘Choose Your Own Adventure’ story that will help you identify any reptile you find in the Northern Territory. Starting with broad questions, the key will ask you more and more specific questions until you end up with a species name for your mystery beast. The keys in this guide cover all taxonomic rankings. If you already know you’re looking at a skink, skip to the Skink chapter and use the key to genera to determine its genus, then move to that genus and use the key to species. An example key for some common inhabitants of a fruit bowl might look something like this: 1. Not orange in colour�����������������������������������2 Orange in colour ���������������������������� orange 2. Yellow in colour��������������������������������������������3 Not yellow in colour�����������������������������������4 3. Elongate and curved in shape�����banana Round to oval in shape ������������������lemon 4. Red in colour������������������������������� red apple Green in colour ��������������������� green apple

You’ll notice that each step has only two, mutually exclusive options. In the first step of our example, you need to xii

determine if your mystery fruit’s colour is orange or not orange. At each step of the key, the group of potential options is divided in two. After continuing through the key, you will eventually be left with just one option and you will have identified your reptile (or piece of fruit). Most of the options in the keys in this guide will relate to morphology or colour pattern. Where morphological differences may be hard to describe in text, we have provided illustrations of the feature discussed. Sometimes, distribution will be used to narrow down the identification. Frustratingly, there will be some situations where the key will be incapable of discriminating between species. Where features to distinguish species are unreliable or not apparent, we have explained these uncertainties below each key. Note that because this is a field guide to the reptiles of the Northern Territory, the keys will only allow you to confidently identify reptiles you find in the Northern Territory. If you use these keys on species from elsewhere in ­ Australia, you might end up with an incorrect identification.

Species profiles Each profile starts with the species’ common and scientific names, followed by a reference for who described it (the author) and when. All species profiles include an adult body size, which tends to be the largest recorded individual. The morphological and colour pattern features of each species are described, with key features useful for identification highlighted in bold. If the species is divided into subspecies, information is provided about how to distinguish the subspecies. Notes are then provided on the species’ known global, national and Northern Territory distribution. Where known, habitat and microhabitat preferences are presented, as is notable

Preface

information on behaviour, breeding and diet. However, if this information is common to all species in the genus, it tends to be presented only in the genus introduction. For all species that are listed as threatened, their conservation status and the jurisdiction of that status are presented. Similar species, from which the species may prove difficult to distinguish, are noted. Any relevant taxonomic notes that require discussion are presented. Each profile includes photos of typical specimens of the species and, where possible, includes photos to document variation within the species.

Measurements Typically, we have provided reptile sizes using maximum recorded measurement for the species, usually from the original description or subsequent publications. Occasionally, when a species is known to get very large but rarely does, more details are given (e.g. king brown snakes [TL 290 cm (commonly 150–200 cm)] and saltwater crocodile [TL 5 m (but with reports of up to 7 m]). Body size measurements are given in group-specific units: carapace length (CL) for turtles; total length (TL) for crocodiles, varanids and snakes; and snout– vent length (SVL) for all other lizards. Tail length will be variable for the many lizards that can drop and regrow their tails, whereas the distance from the snout to the vent will be relatively standard.

Maps Range maps are an extremely important tool for the identification of reptiles. Some species are identified most easily or are disqualified from a list of possibilities by their location. The distribution maps in this book are based on records from the Atlas of Living A ­ ustralia and other sources, plus our own observations. We have confirmed

Map of geographically important towns of the Northern Territory.

or disqualified outlying specimen records by consulting with experts and inspecting museum specimens. Arrows are used to highlight small or isolated populations that might not be immediately discernible. Question marks are used in areas where distributions are uncertain. Our maps include squares that refer to some geographically important towns (see the map above). It is worth noting, however, that reptiles seldom read field guides and do occasionally appear in unexpected places, especially in remote and poorly surveyed regions.

Photographs To show diagnostic characteristics and intraspecific variations in colour and pattern, we have included up to six photos in xiii

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each species account. Where possible, photos of individual animals found in the Northern Territory have been used. However, several species have yet to be photographed within the Northern Territory or have only poor-quality photos available. In these cases, we have sourced photos as close to the Northern Territory as possible

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using individuals that look as we would expect them to in the Northern Territory. Some Northern Territory reptiles have never (e.g. Anilios fossor and A. yirrikalae) or have rarely been photographed in life. In these cases, we have included photos of museum specimens.

Introduction Reptiles of the Northern Territory Australia is a globally recognised hotspot for reptile diversity and endemism and the Northern Territory (‘The Territory’, or simply the ‘NT’) accounts for more than its fair share of this global reptilian acclaim. Although the Northern Territory makes up less than 20% of the A ­ ustralian landmass, despite having relatively uniform topography, it boasts nearly 40% of the country’s reptile species and is home to representatives of every ­Australian reptile

family. A land of extremes, its arid deserts and monsoonal forests harbour some of Australia’s smallest (the dwarf skinks, ­ Menetia spp.) and the world’s largest (the saltwater crocodile) reptiles. It is also home to some of the world’s most venomous snakes, such as the eastern brown snake, coastal taipan and Dubois’ sea snake. While Territorians often find morbid pleasure in boasting about the extreme danger of their reptile fauna, it pales in comparison to the most mundane of everyday

The number of currently recognised reptile species described (at 5-year increments; in blue) and the cumulative number of currently recognised species (in orange) that occur or are suspected to occur in the Northern Territory. A rapid increase in the number of species recognised to occur in the Northern Territory can be observed from the 1960s coincident with increasing accessibility of the Territory, potentially via the advent of four-wheel drive vehicles, as well as Dr Glenn Storr’s prolific tenure at the Western ­Australian Museum. xv

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tasks, such as driving a car or interacting with horses, cattle or dogs. In fact, the vast majority of the Territory’s iconic reptiles, such as frill-necked dragons, thorny devils and central bearded dragons, are perfectly harmless. Reptiles such as ‘ta-ta dragons’ (Gowidon, Lophognathus and Tropicagama spp.), rainbow skinks, snake-eyed skinks and dtella geckos are so commonplace in Territorians’ lives, even in urban areas and backyards, that they barely warrant a passing thought as we go about our daily routines. Reptiles have also been important in the lives of the people indigenous to the Northern Territory for tens of thousands of years and feature heavily in their creation stories and rock art. Currently, there are 368 described species of reptile known to occur on the land and in the sea of the Northern Territory. There are an additional 22 species that, because they occur very close to the Northern Territory border, we suspect may occur in the Northern Territory but have yet to be recorded. The Northern Territory is a vast, rugged and remote expanse of land with an often harsh and brutal climate. Potentially because of this, it boasts the lowest human population density in the country (0.2 people/km2), with fewer than 250  000 people (about 1% of A ­ ustralia’s population) calling the Northern Territory home. Despite the Territory’s ancient history of human habitation, many areas remain under surveyed and poorly known by Western scientists and the true diversity of the Territory’s reptile fauna continues to remain a mystery and a treasure trove of discovery.

Climate, bioregions and habitats of the Northern Territory The Northern Territory has a landmass of over 1.3 million km2, including almost 400 offshore islands, and is A ­ ustralia’s third xvi

largest jurisdiction. The Northern Territory is approximately 1700 km from north to south and 950  km from east to west. Despite its vast size, the Northern Territory is relatively topographically flat (average elevation: 190  m ASL) and lacks any major mountain ranges (highest elevation: Mount Zeil at 1531  m ASL); however, it does have some areas of rugged topography that are rich in endemic species. It can be divided into two broad climatic zones: the wet–dry tropics, and the semi-arid and arid zones. The climatic zones are differentiated primarily on a north–south rainfall gradient, with high annual rainfall in the coastal north and low rainfall in the inland south.

Wet–dry tropics The northern climatic region of the Northern Territory is referred to as the wet–dry, or monsoonal, tropics. This region has a tropical climate with consistently high mean temperatures, variable but typically high humidity, and two distinct seasons – the wet (October to April) and the dry season (May to September). Throughout the year, daytime temperatures average above 30°C every month. Overnight temperatures are highest in the wet season and lowest in the dry season; however, they rarely drop below 14°C even in the coolest months (June and July). Through the dry season, the days are typically warm and sunny, and humidity is relatively low. During this period there is little to no rainfall. As the seasons transition from dry to wet, the temperature and humidity build – a period known as ‘the build-up’  – before relief is provided by monsoonal rains. The wet season is associated with high humidity and rainfall, most of which falls between December and March. During this period, thunderstorms, monsoon systems and cyclones are common. Rainfall during the

Introduction

A

B

C

D

Common habitats of the Northern Territory’s wet–dry tropics: (A) tropical savanna woodland, Darwin area (Etienne Littlefair); (B) monsoon forest, Litchfield National Park (Jules Farquhar); (C) sandstone escarpment, Arnhem Plateau (Brendan Schembri); (D) tropical floodplains, Fogg Dam Conservation Reserve (Jules Farquhar).

wet season is high, with an average of over 1500  mm falling during this period, declining as you move from the coast to the arid interior. The dominant habitat throughout the wet–dry tropics is tropical savanna, generally structured with a Eucalyptus canopy and a grassy understorey. The region is also known for its large, tropical rivers, which are fringed by riparian vegetation, such as mangroves, monsoon forest and paperbark swamps. During the wet season, large rivers regularly break their banks and expand into the surrounding floodplains. Rock escarpments, often sandstone, granite or limestone, are a common feature throughout the wet–dry tropics and their topographical relief provides climatic refuges that diversify the composition of habitats across the landscape. Deeply dissected

rock escarpments provide gorges vegetated with moist monsoon forest. Exposed escarpments with shallow, sandy soils provide purchase for spinifex hummocks (Triodia spp.) and heathlands to dominate, protected from fires that might break out on the surrounding savannas. The savanna of the wet–dry tropics is the most fire-prone biome on the planet and fire is an integral and unavoidable feature of the landscape. During the dry season, the grassy understorey dries and cures and, without intentional ignition, often ignites via lightning strike during severe fire conditions towards the end of the dry season. Fire regimes have been managed by Indigenous people for tens of thousands of years, but have been altered by changing patterns of burning and the introduction of invasive grasses and herbivores since the xvii

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arrival of Europeans in ­Australia. While the Territory’s species have adapted to these historical conditions, altered fire regimes are likely to be responsible for the decline of a number of species.

with slightly higher rainfall, higher humidity and higher winter temperatures. The dominant habitat throughout arid regions of the Northern Territory is desert and xeric shrubland, usually composed of sparse Acacia and Eucalyptus shrubland or woodland, often with a sparse groundcover of hummock grasses. Dominant vegetation types through the semi-arid and arid zones tend to be driven by soil types, with Mitchell grasses (Astrebla spp.) dominating vast blacksoil plains, sparse Acacia shrubs on hard sandplains, and spinifex (Triodia spp.) hummocks dominating gravely, rocky or loose sandy soils. As it is in the tropical north, fire is incredibly important in structuring the Northern Territory’s arid habitats. The finescale application of fire to the landscape generates a mosaic of habitats with differing

Semi-arid and arid zones The southern climatic region of the Northern Territory, situated towards and at the centre of the ­Australian landmass, is composed of semi-arid and arid zones. This vast region has much more variable daily temperatures and more distinct seasons, with very hot summers and cool winters. Humidity is generally relatively low and the little rain that does fall, usually less than 300 mm per year, predominantly falls during the hottest months (October to March). The Northern Territory arid zones have a more tropical influence in the north, A

B

C

D

Common habitats of the Northern Territory’s semi-arid and arid zones: (A) Arid escarpment, Ormiston Gorge, West MacDonnell (Tjoritja) National Park (Jules Farquhar); (B) desert sand dune, near Yulara, Great Sandy Desert (Stephen Zozaya); (C) blacksoil plains, Barkly Tablelands, Mitchell Grass Downs (Brendan Schembri); (D) stony, spinifex-dominated plain, Tanami Desert (Brendan Schembri). xviii

Introduction

degrees of openness at various post-fire ages. Such fire regimes had been maintained by Indigenous people for tens of thousands of years, but have been disrupted recently. Unfortunately, large swathes of arid hummock grasslands and riparian strips have been converted to invasive buffel grasslands with a vastly different burning profile. The Northern Territory’s arid zone is host to an incredible diversity of reptiles, particularly lizards. Although they look fairly homogenous, the spinifex hummock grasslands that dominate this vast region provide perfect habitat for reptiles by creating a range of cool, humid, structurally complex microhabitats protected by an impenetrable matrix of spines. A footy field sized area of Northern Territory arid grassland can be home to many more species of reptile than some entire countries.

Bioregions Within these broad climatic zones, the Territory can be further subdivided into bioregions, which can inform our understanding of the biota of a given area. Bioregions are a landscape-scale approach to classifying the environment using geology and vegetation. Twenty-five bioregions have been identified in the Northern Territory, many of which host unique compositions of reptile fauna and some host regionally endemic reptile species. Where informative, we have referred to the bioregions that individual reptile species occupy.

Reptile biogeography in the Northern Territory Understanding the structural and functional features of the landscape at different spatial scales is key to understanding the

xix

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composition and distribution of ­Australian fauna. The structural and function composition of the landscape is affected by temperature, rainfall, geology, soil and elevation, which determine vegetation composition, thermal niches and local reptile abundance, species richness and composition. Some reptiles are extremely widespread, and are habitat and climatic generalists that have very few specific requirements that need to be met to occur in an area (e.g. Children’s python, Antaresia childreni; Burton’s snakelizard, Lialis burtonis). As a result, these species can be encountered in most habitats throughout the Northern Territory. Others, however, have very specific habitat and climatic requirements (e.g. dappled snakeeyed skink, Cryptoblepharus daedalos; Arnhem phasmid gecko, Strophurus horneri) and have exceptionally small distributions. Biogeography, however, is incredibly complex and the current habitat and climate cannot entirely explain why and where species occur without a deeper appreciation for species interactions, and geological and evolutionary history.

Threats to reptiles in the Northern Territory While ­Australian reptiles appear to have avoided the precipitous population declines experienced by our native birds and mammals following the arrival of Europeans, there are a number of threatened reptiles and numerous species have suffered declines in recent decades. Unfortunately, potentially because people have tended to view reptiles as at less risk than other groups of native animals, our understanding of their conservation status and the threats to them in the Northern Territory is undermined by a lack of monitoring and research. We do, however, have some evidence that reptiles are vulnerable to many of the same threats facing other xx

­ ustralian animals, such as mammals and A birds, that have enjoyed significantly more research interest and investment. These threats include invasive plants and animals, habitat clearance, changed land practices, wild harvesting, altered fire regimes and climate change.

Invasive plants and animals When we think of the impact of invasive species on reptiles in northern A ­ ustralia, there is undoubtedly a rough-skinned, hopping invader at the forefront of everyone’s mind. Cane toads (Rhinella marina), native to South America, invaded the Northern Territory via Queensland in the early 1980s and have since proceeded to colonise all of the Territory’s mainland wet–dry tropics. As the toads advanced across the Territory, many of our hapless native reptile predators mistook these amphibian invaders for an easy meal  – which they were, but at a huge cost. Because Australia has no native toads, most ­ ­Australian reptiles have no evolutionary history with true toads and their chemical defences and are extremely vulnerable to their toxic secretions. In fact, many are so sensitive that merely biting or mouthing a toad proves fatal. The fallout from the arrival of cane toads in the Northern Territory appeared stark and severe. Some of our most beloved and conspicuous large reptilian predators, such as northern bluetongues (Tiliqua scincoides intermedia), yellow-spotted monitors (Varanus panoptes), king brown snakes (Pseudechis australis), plains death adders (Acanthophis hawkei) and some populations of freshwater crocodiles (Crocodylus johnstoni) suffered precipitous population declines. The impact of cane toads on reptiles has probably attracted more research than just about any other threat to ­Australian reptiles, and the – sometimes nuanced – nature of their

Introduction

impact is becoming clearer. Some reptiles are severely impacted, while others indirectly benefit (reviewed in Shine 2010). However, the vehement hatred of toads is such that they are regularly blamed for any and all perceived population changes in Northern Territory reptiles. There are, of course, numerous other potential threats to the reptiles of the Northern Territory, some of which risk being overlooked due to the impact of the highly visible toad. Invasive predators, such a feral cats and red foxes, are thought to be responsible for most A ­ ustralian mammal extirpations and extinctions since European arrival, and feral cats have been implicated in northern Australia’s recent and severe mammal ­ declines. In the Northern Territory, cats occur throughout the mainland and on many offshore islands, while foxes are restricted to more arid areas south of about Elliott. Reptiles are known to be important prey items for cats and foxes, particularly in the arid zone, and cats alone are estimated to eat over 450 million ­Australian reptiles a year (Woinarski et al. 2018). Yet, little is known about the impacts of these feral predators on reptiles in the Northern Territory. Clearly, elevated mortality rates due to invasive predators could result in significant population declines, and research and monitoring of this potential impact are warranted. Feral herbivores, such as buffalo, camels, cattle, donkeys, horses and pigs, are abundant across the Northern Territory. Through trampling, wallowing, herbivory and defecation, feral herbivores impact on the environment by altering the structure, composition and functioning of ecosystems. Feral herbivores have recently been implicated in northern mammal declines and, although information is lacking, they are also probably having negative impacts on populations of reptiles. The impact of

feral herbivores on reptiles in the Northern Territory is likely to be felt most severely by species that rely on fragile habitat components, such a spinifex, burrows and fallen hollow logs, which are often destroyed where herbivores are abundant. Because they are opportunistic omnivores, feral pigs may also be impacting reptile populations by digging up and eating their eggs – a particular threat to sea and freshwater turtles. An overlooked potential impact of invaders on reptiles in the Northern Territory is the impact of invasive vegetation, such as gamba grass (Andropogon gayanus) and buffel grass (Cenchrus ciliaris). These introduced pasture grasses are a major threat to native grasslands and woodlands because they transform plant communities, change vegetation structure and alter fire regimes. For example, the tropical savanna woodlands of the Northern Territory’s Top End are progressively being turned into invasive tropical grasslands because of the spread of gamba grass. Gamba grows much taller and denser than native grasses, and burns at far greater heights into the canopy and at far greater temperatures, often killing the native canopy and promoting the growth of more gamba. Similarly, in more arid systems, vast plains of buffel grass are progressively replacing native grasslands, such spinifex sandplain, resulting in simplification and degradation of these complex arid systems. Such changes to vegetation structure and function are bound to have profound impacts on local reptile populations.

Habitat clearing and changed land practices Much of the Northern Territory is relatively unaltered by land clearing and development. However, urban, rural, industrial, mining and agricultural development all xxi

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require habitat clearing and changed land practices, which alter the structure and function of ecosystems, sometimes irreversibly. Habitat clearing is likely to have the most immediate, severe and long-­ lasting impact on local fauna because it typically removes all ecosystem features and functions that sustain native flora and fauna. Habitat clearance imposes the most severe impacts on habitat specialist species with small distributions. For instance, the yellow-snouted gecko (Lucasium occultum), Kurnbudj ctenotus and Stuart’s ctenotus (Ctenotus kurnbudj and C. stuarti) all occupy specific habitats in a small area between the Mary and South Alligator rivers in the western Top End. Although some of this habitat is protected by the north-western edge of Kakadu National Park, conversion of the Point Stuart area to intensive agricultural practices, such as cotton production, could remove a considerable portion of the habitat required by these species to persist. The majority of the Northern Territory is designated as pastoral land, much of which is managed as cattle properties. However, most cattle stations in the Territory stock cattle on native habitats, which, unlike their southern counterparts, are not entirely cleared. Given the proportion of land designated to pastoral activities, striking a balance between land management for both pastoral and biodiversity outcomes is paramount to the conservation of all native species in the Northern Territory.

Wild harvesting In the scheme of things, wild harvesting appears to be a fairly minor threat to the reptiles of the Northern Territory. The impact of the harvesting of reptiles for food, such as the eggs and adults of sea turtles and goannas, by Indigenous people xxii

almost certainly pales in comparison to the impact caused by car and boat strikes and invasive species. However, some species in some locations may be so imperilled by other threats, such as feral predators, pigs and cane toads, that they may require a reduction in hunting pressure while populations recover. While some species of reptiles are targeted by illegal collectors for the pet trade, there is currently no evidence that this has caused population-level impacts to any reptile species in the Northern Territory. However, illegal reptile collectors are known for their unscrupulous methods of pillaging reptiles from the landscape, which can cause considerable damage to local habitats by overturning and destroying rocks, breaking open tree hollows and removing loose bark from trees. Such destructive activities are likely to have a far more pervasive and long-term impact on reptiles than the removal of individuals from the area. One of the larger impacts of wild harvesting that is seemingly overlooked is the impact of fishing trawlers on sea snakes. Annually, thousands of sea snakes are caught in fishing trawler nets throughout waters off the coast of the Northern Territory. While many are released alive, plenty are killed in the nets, and those that are released are likely to be released some distance from where they were collected, potentially injured and into unsuitable habitat. It is currently unknown what impact this may be having on sea snake populations.

Altered fire regimes The Northern Territory has some of the most fire-prone habitats on the planet, particularly the northern tropical savannas. For tens of thousands of years Indigenous people have burnt the Northern Territory to

Introduction

promote movement through the landscape and fresh vegetation growth, and to improve hunting. Traditional Indigenous fire management typically involves deploying cool, patchy burns early in the dry season that reduce grass fuel loads. Traditional burning creates mosaics of habitats of different ages, to which the fauna of ­Australia has adapted. It also creates firebreaks in the landscape that help stop larger and far more severe fires late in the dry season. Unfortunately, the arrival of Europeans has altered these fire regimes via the removal of traditional burning practices, the introduction of invasive weeds and changes to landscape structure. Altered fire regimes are known to threaten thousands of species worldwide and are probably having a considerable impact on some reptiles of the Northern Territory, particularly those that require long-unburnt habitats for persistence. Considerably more research should be directed towards investigating the impacts of altered fire regimes on populations of reptiles in the Northern Territory.

Climate change The climate of the Northern Territory is often brutal. Although renowned for its

extreme temperature and humidity, long periods of drought, epic thunderstorms, flooding monsoons, destructive cyclones and little in the way of topography to provide climatic refugia, species native to the Northern Territory are adapted to these climatic conditions. However, many animals living in the Northern Territory are likely to already be at the limits of their climatic tolerance, with little relief to be found by way of range shifts across rainfall, temperature or elevational gradients. Rapid human-induced climate change has begun and will continue to affect the Northern Territory, including by increasingly intense and unpredictable rainfall events, longer droughts, increasing average temperatures, increasing frequency of temperature extremes, sea level rise and saltwater intrusion, and altered fire behaviour and severity. As ectotherms, reptiles are beholden to the prevailing weather conditions for all their biological functions, and although they can adapt to changing conditions, changes that are too rapid or extreme are likely to result in population declines, range contractions, reductions in niches, skewing of sex ratios in species with temperature-dependent sex determination and, in the most severe instances, extinction.

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Crocodilians (Order Crocodilia) Family Crocodylidae Crocodiles genus Crocodylus Laurenti, 1768 Crocodilians first appeared 95 million years ago and are an order of predominantly large, semi-aquatic, predatory reptiles divided into three ancient families  – ­Alligatoridae (alligators and caimans), Gavialidae (­gharial and false gharial) and Crocodylidae (true crocodiles). In ­Australia, crocodilians are represented by ‘true crocodiles’ (Crocodylidae) in a single genus (Crocodylus). True crocodiles are composed of three extant genera (Crocodylus, Mecistops and Osteolaemus) with a global distribution from the Western Pacific, through Asia, Africa, and North and South America. Globally, there are 13 species in the genus Crocodylus; two species are found in ­Australia, one of which is endemic to A ­ ustralia (Crocodylus johnstoni) and the other of which has a much broader distribution (Crocodylus porosus). Both species occur in the Northern Territory. Crocodilians include the largest living reptiles on the planet. We now know that crocodilians are the closest living relatives of birds, and are more closely related to birds and dinosaurs than they are to other reptiles. Despite their prehistoric appearance, crocodiles are one of the most biologically advanced reptiles, with a four-chambered heart, cerebral cortex and the functional equivalent of a diaphragm. Crocodiles are unmistakeable from any other group of Australian reptiles. They possess long, ­ streamlined bodies armoured with bony, sometimes keeled, plates (osteoderms); powerful, laterally compressed tails; short,

robust limbs with webbed feet; eyes set on top of their head, which can be retracted into their skull; elongate snouts with nostrils set high above the tip to allow them to breathe while their body is submerged; and powerful jaws lined with long, conical teeth. Australian crocodiles are largely ambush hunters. While they are regularly observed basking and hunting during the day, they are most active at night. Crocodile skull, snout and tooth morphology is driven by diet. Species that predominantly eat smaller, soft-bodied prey (e.g. freshwater crocodiles) have slender jaws that can be swiftly swiped through the water to catch their agile quarry. Species with more varied diets (e.g. saltwater crocodiles) that include large, hard- and/or heavy-bodied prey that require crushing or dismemberment before being consumed have broad snouts with extremely powerful jaws and muscles. All crocodiles are oviparous, laying eggs in an excavated hole (e.g. freshwater crocodiles) or in a mound constructed from vegetation (e.g. saltwater crocodiles). Despite their fearsome reputation as brutal predators, some crocodiles, including both ­Australian species, exhibit maternal care. Female saltwater crocodiles in particular are extremely attentive mothers, displaying some of the most sophisticated maternal care among reptiles. After constructing the nest and laying her eggs, a female crocodile will guard the nest from any threats (including people) throughout the entire incubation period. During hatching, the young crocodiles will call out to their mother, who will gently excavate the nest and delicately carry them to the water in her powerful jaws. 1

F i e l d G u i d e t o t h e R e p t i l e s o f t h e N o r t h e r n Te r r i t o r y

Saltwater (Crocodylus porosus) (right) and freshwater crocodiles (C. johnstoni) (left) cooccur in many Northern Territory waterways. Daly River, NT. Brendan Schembri.

Saltwater crocodiles are the world’s largest living reptiles with the strongest bite force of any living animal. They are a formidable predator and are by far the most dangerous reptile in A ­ustralia. Adult saltwater crocodiles are sufficiently large that humans fall well within the size of their natural prey, and they have been responsible for a number of human fatalities. Extreme caution should be taken near waterways in saltwater crocodile habitat in the Northern Territory.

Key to Crocodylus of the Northern Territory 1. Relatively slender snout (A); a single row of enlarged nuchal shields, separated from the smooth-skinned parietal region by fewer than eight granular scales (A)�������C. johnstoni Relatively broad snout (B); two rows of enlarged nuchal shields, separated from the smooth-skinned parietal region by more than eight granular scales (B)���������C. porosus

A

B

Freshwater crocodile Crocodylus johnstoni Krefft, 1873

TL 3  m. A moderately sized crocodile with a relatively narrow snout; and enlarged nuchal shields in a single row that is separated from the smooth-skinned parietal region by fewer than eight scales. Dorsal surface olive–green to dark brown with darker brown to black markings often coalescing to form incomplete dorsal cross-bands. Ventral surface paler than dorsum. Notes: Endemic to ­Australia. Found across much of northern ­Australia, from the interior of Far North Qld to the Kimberley region, WA. It occurs through much of northern NT. Predominantly found in 2

Crocodylus johnstoni. Daly River, NT. Brendan Schembri.

freshwater rivers, creeks and billabongs. Can be found in smaller, more inland reaches of waterways than saltwater crocodiles, but the two species are regularly found in sympatry. Feeds on crustaceans, fish, frogs, reptiles, birds and small

Crocodilians

mammals, such as flying-foxes. In some locations, it has been significantly impacted by cane toads (Rhinella marina). While generally not considered dangerous to humans, care should still be taken around it as it can bite and cause serious injuries if threatened or surprised. Similar species: C. porosus

Saltwater crocodile; estuarine crocodile Crocodylus porosus Schneider, 1801

TL 5 m (but with reports of up to 7  m). An enormous crocodile with a relatively broad snout; and two rows of enlarged nuchal shields, separated from the smooth-skinned parietal region by more than eight granular scales. Dorsal surface grey, green to almost black with darker mottling. Ventral surface paler than dorsum. Females are considerably smaller and more lightly built than males, rarely exceeding 3  m in length. Notes: Found from eastern India, through South-East Asia, New Guinea, northern ­ Australia and Micronesia. Despite their name, saltwater crocodiles inhabit saltwater, brackish and freshwater. While they are

Crocodylus porosus. Daly River, NT. Brendan Schembri.

most common in major rivers, floodplains and billabongs within 100 km of the coast, they also inhabit some inland waterways more than 200 km from the coast, such as in the Katherine region. Typically inhabit floodplains, creeks, rivers, estuaries, and coastlines, and will cross open ocean to reach offshore islands. Feed on crustaceans, fish (including sharks and rays), birds, mammals and reptiles (including other crocodiles). Known to kill and eat people. Extreme caution should be exercised around any waterways that are potentially inhabited by saltwater crocodiles. VERY DANGEROUS. Similar species: C. johnstoni

3

Turtles and tortoises (Order Testudines) Turtles and tortoises (testudines) are an iconic, unmistakeable group of reptiles. While the entirely terrestrial species are known as tortoises and the entirely marine species are known as turtles, the freshwater species have been referred to as both turtles and tortoises. Nowadays, most A ­ ustralian sources (including this guide) refer to them as freshwater turtles. A ­ustralia has no

terrestrial tortoises, but we do have a diverse array of marine and freshwater turtles. A ­ ustralian coastal waters are home to six of the world’s seven marine turtle species, with representatives from both families (Cheloniidae and Dermochelyidae). Our native freshwater turtle species are divided into two families: Chelidae, with 24 species; and Carettochelydidae, containing

Carapace and plastron of a chelid turtle (Chelodina canni) showing the position and name of scutes from a dorsal and ventral perspective.

Carapace and plastron of a cheloniid turtle (Chelonia mydas) showing the position and name of scutes from a dorsal and ventral perspective. 4

Tu r t l e s a n d t o r t o i s e s

only the Northern Territory endemic pignosed turtle (Carettochelys insculpta). While their movements on land are somewhat ungainly, both marine and freshwater turtles are graceful and efficient swimmers

when in the water. All turtles possess a hard, bony shell (made up of many small bones covered in soft flesh in the case of the leatherback turtle), composed of a carapace (upper half) and a plastron (lower half).

Key to the turtles of the Northern Territory 1. Both forelimbs and hindlimbs are paddle-shaped, without webbed, clawed feet (A)����������2 Forelimbs and hindlimbs not paddle-shaped, with webbed, clawed feet (B)�����������Chelidae (side-necked turtles) 2. Nostrils level with the surface of the snout, no fleshy proboscis present; marine-dwelling����������������������������������������������������������������������������������������������������������������������������������������������3 Nostrils at the end of a tubular, fleshy snout or proboscis; mostly freshwater-dwelling�������������������������������������������������������������� Carettochelydidae (pig-nosed turtle) 3. Limbs with claws (A)����������������������������������������������������������������������������������������Cheloniidae (sea turtles) Limbs without claws (C)��������������������������������������������������������� Dermochelyidae (leatherback turtle)

A

B

C

Key to marine turtle tracks of the Northern Territory 1. Tracks with alternating pattern, flipper marks alternate (A)������������������������������������������������������������2 Tracks with breaststroke pattern, flipper marks side by side (B)����������������������������������������������������3 2. Plastron skid narrower than width of hind flipper tracks������������������������������������� Caretta caretta Plastron skid wider than or equal to width of hind flipper tracks*�������������������������������������������������������������������Eretmochelys imbricata or Lepidochelys olivacea 3. Track width 2 m���������������������������������������������������������������������������������������������������Dermochelys coriacea 4. Front flipper tracks approximately as wide as hind flipper tracks ������������������Chelonia mydas Front flipper tracks much narrower than hind flipper tracks����������������������� Natator depressus *

It is not possible to reliably distinguish the tracks made by hawksbill (Eretmochelys imbricata) and olive ridley turtles (Lepidochelys olivacea). 5

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A

Sea turtles Family Cheloniidae This family includes six of the world’s seven extant sea turtles. These large, longlived, marine turtles occur throughout tropical and warm temperate waters across the globe. ­ Australia’s coastal waters are home to five of the six species, with one species (the flatback turtle, Natator depressus) being endemic to A ­ ustralia. All five species are found in Northern Territory waters. Despite their ancient origins – ­cheloniid turtles emerged over 100 million years ago  – sea turtles have not undergone significant morphological diversification and so can be tricky to distinguish from one another. All sea turtles have a streamlined bony shell, paddle-like flippers and beaklike mouthparts. Unlike their terrestrial counterparts, sea turtles are unable to retract their head into their shell. While there is some variation in the body size of sea turtles, most attain impressively large adult body sizes, with the largest species reaching over a metre in carapace length and weighing well over 100 kg. Cheloniidae can be distinguished from other turtles in the Northern Territory by the presence of paddle-shaped forelimbs and hindlimbs; clawed flippers; and nostrils that are level

6

B

with the surface of the snout (i.e. no fleshy proboscis present). Although sea turtles are aquatic for nearly their entire lifecycle, they are still egg layers and so females will periodically haul themselves up onto a beach (usually at night), excavate a nest using their flippers, and lay eggs the size and shape of pingpong balls. They then laboriously cover the nest back up with sand and drag themselves back down to the water. Depending on the species and condition of the turtle, this might be repeated several times during a nesting season, spaced about 2 weeks apart. Female sea turtles typically nest only every 2–4 years. Apart from the loggerhead turtle, all ­Australian species are known to nest on beaches in the Northern Territory. Nesting occurs primarily on the beaches of the north-western and north-eastern Top End mainland and on offshore islands, such as Groote Eylandt and the outer Pellew Islands. The sea turtle reproductive strategy is to lay a lot of eggs over a long lifetime. Very few of these eggs survive to adulthood, but as long as a few make it, populations can persist. Unfortunately, human activities have resulted in a huge increase in mortality of sea turtles at all life stages. Eggs have always been vulnerable to natural predators, such as goannas and dingoes.

Tu r t l e s a n d t o r t o i s e s

However, they now have to contend with introduced predators, such as pigs; being destroyed by inundation  – which will become increasingly worse as sea levels rise; and extreme temperatures  – predicted to worsen as climate change becomes more severe. Hatchlings that survive in nests to full term synchronise hatching and rush down to the water as a group. During this dash down the beach and through the shallows, hatchlings are feasted upon by waiting predators, such as crabs, gulls and fish. Hatchlings typically orient themselves towards the ocean by moving away from dark silhouettes and towards light reflecting off the ocean. This means they can easily be confused by beachside lighting and will sometimes head away from the water and

towards these artificial lights. Adults have natural predators, such as tiger sharks and saltwater crocodiles, but are also killed by boat strikes and entanglement in fishing gear. Despite seemingly healthy adult population sizes, we may see precipitous declines in the future if too few hatchlings survive to adulthood to replace an ageing adult population. Because of these threats, many sea turtles are vulnerable to extinction. Sea turtles and their eggs have been harvested for food by Indigenous people in ­Australia for tens of thousands of years and continue to be an important part of the diet and culture of Indigenous people in the Northern Territory, as evidenced by their frequent depiction in rock art sites across the Top End.

Key to Cheloniidae of the Northern Territory 1. Five (A) or more (B) costal shields on each side of carapace������������������������������������������������������������2 Four costal shields on each side of carapace (C)����������������������������������������������������������������������������������3 2. Five (rarely six) costal shields on each side of carapace (A); carapace longer than wide (A); dorsal colouration of adults and hatchlings usually reddish brown; four enlarged inframarginals (D) without pores��������������������������������������������������������������������������������������������������Caretta Six or more costal shields on each side of carapace (B); carapace more or less circular (B); dorsal colouration of adults olive–grey and hatchlings slate grey; usually three enlarged inframarginals (E) with or without pores������������������������������������������������������������������������Lepidochelys 3. One pair of prefrontal shields (F); tip of upper jaw not projecting forwards and downward to form a narrow, protrusive beak (G)������������������������������������������������������������������������������������������������������4 Two pairs of prefrontal shields (H); tip of upper jaw projecting forwards and downwards to form a narrow, protrusive beak (I)��������������������������������������������������������������������������������Eretmochelys 4. Usually four or more postoculars (J); in adults, high-domed carapace without upturned lateral edges and with distinct sutures between shields; a series of enlarged scales on the upper eyelid, the largest of which are at least half the width of the adjoining prefrontal ���������������������������������������������������������������������������������������������������������������������������������������������������������������Chelonia Three postoculars (K); in adults, low-domed carapace with upturned lateral edges and smooth appearance due to indistinct sutures between shields; upper eyelid composed of numerous, small, irregular scales, the largest of which are much less than one-quarter the width of the adjoining prefrontal ����������������������������������������������������������������������������������������������� Natator

7

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A

E

I

B

C

F

G

J

Genus Caretta Rafinesque, 1841 A monotypic sea turtle genus with a global tropical and subtropical distribution. In Australia, they typically inhabit coastal ­ waters from WA to NSW. Hatchlings tagged in A ­ ustralia are known to disperse as far as South America, spending around 15  years at sea before returning to ­Australian waters. Female loggerhead turtles reach breeding age at around 30 years. Loggerhead turtles are the only species of Australian sea turtle that has not been ­ recorded nesting on NT beaches. Loggerhead turtles can be distinguished from other sea turtles by the following characteristics: large head, especially on older individuals; five (rarely six) costal shields on each side of carapace; carapace longer 8

D

H

K

than wide; dorsal colouration of adults and hatchlings reddish brown; and four enlarged inframarginal scales without pores. Loggerheads are carnivorous and feed on a range of marine invertebrates, such as jellyfish, crustaceans and molluscs.

Loggerhead turtle

Caretta caretta (Linnaeus, 1758) CL 1.25 m. A large, robust sea turtle with a disproportionally massive head, especially in older individuals, and two pairs of prefrontal shields. Carapace longer than wide and roughly heart-shaped with five (rarely six) pairs of costal shields. Dorsal colouration of adults and hatchlings usually reddish brown to

Tu r t l e s a n d t o r t o i s e s

Caretta caretta. Nesting adult female. Mon Repos, Qld. Steve Wilson.

Caretta caretta. Hatchling. Mon Repos, Qld. Steve Wilson.

brown, sometimes irregularly speckled with darker brown. Whitish or cream below. Notes: Occurs worldwide in tropical and warm temperate waters, occasionally venturing into cooler temperate waters. Recorded from the entire

coastline of ­Australia; however, most common in waters off the east coast. Appears to forage in deeper water. Vulnerable (NT; IUCN Red List); Endangered (Commonwealth). Similar species: Lepidochelys olivacea

Genus Chelonia Sonnini & Latreide, 1802

and with distinct sutures between shields. Although juveniles are carnivorous, adults appear to be almost entirely herbivorous. The name ‘green turtle’ comes from the greenish colouration of the animal’s fat, which is a result of its herbivorous diet high in seagrass.

A monotypic sea turtle genus with a global tropical and subtropical distribution. In ­Australia, they typically inhabit northern and eastern coastal waters, but are often observed in the brackish reaches of large NT rivers. Although green turtles are probably the most commonly observed sea turtle in waters around the NT, they restrict most of their nesting activity to North East Arnhem Land, Groote Eylandt and the Pellew Islands where they nest in high densities on wide beaches backed by large dune systems. Green turtles can be distinguished from other sea turtles by the following characteristics: four costal shields on each side of carapace; one pair of prefrontal shields; usually four or more postoculars; a series of enlarged scales on the upper eyelid, the largest of which are at least half the width of the adjoining prefrontal; and, in adults, a high-domed carapace without upturned lateral edges

Green turtle

Chelonia mydas (Linnaeus, 1758) CL 1.5 m. A very large sea turtle with a beak-like snout and a single pair of prefrontal shields. Carapace is highdomed, with four pairs of costal shields and without upturned edges. Dorsal colouration olive–green, usually variegated with brown, reddish brown and black. Whitish or cream below. Notes: Occurs in pantropical waters worldwide. Occurs throughout waters off the coast of northern and eastern ­Australia. In the NT, very common in coastal waters and up brackish rivers. Near Threatened (NT); Vulnerable (Commonwealth); Endangered (IUCN Red List). Similar species: Eretmochelys imbricata; Natator depressus 9

F i e l d G u i d e t o t h e R e p t i l e s o f t h e N o r t h e r n Te r r i t o r y

Chelonia mydas. Darwin Harbour, NT. Nick Volpe.

Genus Eretmochelys Fitzinger, 1843 A monotypic sea turtle genus with pantropical global distribution. In ­Australia, they occur in warm, usually tropical waters from mid-coast WA to southern Qld, particularly in the vicinity of coral reefs. Female hawksbill turtles reach reproductive age at around 30 years. They will nest every 2–4 years, laying up to six clutches of about 120 eggs in a season. After hatching, baby hawksbill turtles will swim for several days out into the open ocean. They will drift out here for 5–10  years, before returning to coastal waters as juveniles. Although hawksbill turtles are not uncommon in NT waters, they infrequently breed and nest in the NT. Hawksbill turtles can be distinguished from other sea turtles by the following characteristics: four pairs of costal scales on each side of carapace; thick, overlapping carapace shields; two pairs of prefrontal shields on snout; and tip of upper jaw projects forwards and downwards to form a narrow, protrusive beak. Hawksbill turtles get their name from their pointed, bird-like beak which they use to extract sea sponges from cracks and crevices in corals and rocks. They will also feed on soft coral, seagrasses, and algae. 10

Chelonia mydas. Hatchling. Groote Eylandt, NT. Hal Cogger.

Hawksbill turtle

Eretmochelys imbricata (Linnaeus, 1766) CL 1 m. A distinctive sea turtle with a pronounced, protrusive beak-like snout and two pairs of prefrontal shields. Carapace

Eretmochelys imbricata. Port Douglas, Qld. Etienne Littlefair.

Eretmochelys imbricata. Hatchling. Mount Adolphus Island, Qld. Steve Wilson.

Tu r t l e s a n d t o r t o i s e s

with overlapping shields, often serrated-edged and with four pairs of costal shields. Dorsal colouration olive–green to brown, variegated with rich reddish to black. Whitish to yellowish below. Subspecies: Two subspecies; only E.  i.  bissa (Rüppell, 1835) occurs in ­Australia. Eretmochelys i. imbricata (Linnaeus, 1766)

occurs in the Atlantic Ocean. Notes: Occurs in pantropical waters worldwide, especially around coral reefs. In ­Australia, usually found from mid WA, across northern A ­ ustralia to southern Qld. Vulnerable (NT; Commonwealth); Critically Endangered (IUCN Red List). Similar species: Chelonia mydas; Natator depressus

Ridley turtles genus Lepidochelys Fitzinger, 1843 Ridley turtles are the only genus of sea turtles containing more than a single species. There are two species of Lepidochelys, one of which is found in ­Australian waters. Kemp’s ridley turtles (Lepidochelys kempii) are found along the North American east coast, with occasional records from elsewhere in the Atlantic Ocean. Olive ridley turtles (Lepidochelys olivacea) have a pantropical global distribution. Although globally one of the most abundant and widespread sea turtles, ridley turtles have a smaller A ­ ustralian distribution than the other sea turtles, predominantly being restricted to the tropical northern waters of WA, NT and Qld. Ridley turtles can be distinguished from other sea turtles by the following characteristics: six or more pairs of costal shields on each side of carapace; usually three enlarged inframarginals with or without pores; and a more or less circular carapace. Ridley turtles are predominantly carnivorous and feed on a range of marine invertebrates, such as urchins, crabs and jellyfish.

Olive ridley turtle; Pacific ridley turtle Lepidochelys olivacea (Eschscholtz, 1829)

CL 60–80 cm. A smallish sea turtle with two pairs of prefrontal shields. Carapace roughly circular with six or

Lepidochelys olivacea. Elcho Island, NT. Ian Morris.

Lepidochelys olivacea. Hatchling. Cape Keerweer area, Qld. Anders Zimny.

more pairs of costal shields. Plastron usually with three enlarged inframarginal scales, with or without pores. Adults usually olive– grey above, usually without any darker markings, and whitish below. Hatchlings are slate grey above and dark brown below. Notes: Occurs in pantropical waters worldwide, particularly in the Pacific and Indian Oceans. Uncommon in ­Australia and mostly restricted 11

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to the tropical, coastal waters off north-western NT and Cape York Peninsula, Qld. Usually inhabits shallow, soft-­bottomed waters. In the NT, nests are predominantly laid on island

beaches off the northern coast of the Top End and in the Gulf of Carpentaria. Vulnerable (NT; IUCN Red List); Endangered (Commonwealth). Similar species: Caretta caretta

Genus Natator McCulloch, 1908

heart-shaped, with four pairs of costal shields and upturned edges. Dorsal colouration of adults largely patternless and grey or greenish and whitish or cream below. Skin along sides neck often flushed yellowish brown. Hatchlings have darker margins to their carapace shields, giving them a reticulated pattern. Notes: Endemic to ­Australian waters. Occurs in warm waters off the coast of

A monotypic sea turtle genus and the only sea turtle endemic to Australasian waters, with all known nesting beaches in ­Australian territory. Females lay relatively small clutches of about 50 large eggs. Hatchling flatbacks emerge larger than other sea turtles and tend to stay close to the shore, lacking the pelagic phase of other hatchling sea turtles. Flatbacks are very common in NT waters and nest on virtually all suitable beaches along the entire NT coastline, including offshore islands. Flatbacks can be distinguished from other sea turtles by the following characteristics: four costal scales on each side of the carapace; one pair of prefrontal scales; three postocular scales; upper eyelid composed of numerous, small, irregular scales, the largest of which are much less than one-quarter the width of the adjoining prefrontal; and, in adults, low-domed carapace with upturned lateral edges and smooth appearance due to indistinct sutures between shields. Predominantly carnivorous and feeds mostly on soft-bodied marine invertebrates, such as soft corals, sea cucumbers and molluscs.

Natator depressus. Nesting adult female. Kirk River area, Qld. Anders Zimny.

Flatback turtle

Natator depressus (Garman, 1880) CL 80–100 cm. A moderately sized sea turtle with a single pair of prefrontal shields. Smooth-looking carapace is low-domed and roughly

12

Natator depressus. Hatchling. Kirk River area, Qld. Anders Zimny.

Tu r t l e s a n d t o r t o i s e s

northern ­Australia, from mid WA to southeastern Qld. Usually inhabits shallow, softbottomed waters. Data Deficient (NT; IUCN

Red List); Vulnerable (Commonwealth). Similar species: Chelonia mydas; Eretmochelys imbricata

Leatherback turtle Family Dermochelyidae

to match. Leatherbacks subsist almost entirely on jellyfish and, to assist with the movement of their gelatinous prey down to their gut, their oesophagus is lined with recurved spines. Despite this seemingly simple, nutrient-poor diet, this species attains sizes far larger than any other turtle, with individuals having been recorded in excess of 600 kg. Unfortunately, because plastic bags resemble their jellyfish prey so closely, leatherbacks are commonly recorded having consumed and been killed by discarded bags. Incredibly, leatherbacks are unique among living reptiles in their ability to consistently maintain their body temperature above the temperature of the external environment. Turtles have been recorded with body temperatures up to 18°C above the frigid 7°C surrounding water temperature. This ability enables them to occur in areas beyond the reach of all other extant marine turtles. They can also dive to impressive depths, with individuals having been recorded diving to depths exceeding 1200 m.

Genus Dermochelys Blainville, 1816 The sole genus in the family, with only a single extant species in the genus. This enormous, highly specialised turtle has the largest distribution of any reptile, extending from within the Arctic Circle to south of New Zealand. Its widespread, pelagic distribution extends into temperate seas which experience much lower temperatures than those inhabited by most other marine turtles. Despite this, the species only nests in the tropics. While adults have been observed around most of the ­Australian coast, the species rarely breeds in ­ Australia. Leatherbacks are seldom sighted in waters off the Northern Territory coast and there are only a handful of records of them nesting on beaches of the Cobourg Peninsula, Northern Territory. Leatherback turtles are morphologically distinctive, with a shell made up of small bones (osteoderms) embedded in the leathery skin that gives this turtle its name. These osteoderms are enlarged in longitudinal ridges, giving rise to seven keels running down the carapace and four keels on the plastron. Leatherbacks can be easily distinguished from all other A ­ ustralian turtles by the presence of these keels, along with paddle-shaped forelimbs and hindlimbs; flippers lacking claws; and nostrils level with surface of snout (i.e. no fleshy proboscis present). Leatherbacks have a highly specialised life history and diet with exceptional morphological and physiological adaptations

Leatherback turtle Dermochelys coriacea (Vandelli, 1761)

CL 3 m. A very large, distinctive, streamlined marine turtle with leathery skin rather than a hard shell. Embedded within the skin are many small dermal bones (called osteoderms) that provide structure and protection. Rows of these osteoderms are enlarged to form seven longitudinal ridges along the carapace, and four ridges along the plastron. Usually 13

F i e l d G u i d e t o t h e R e p t i l e s o f t h e N o r t h e r n Te r r i t o r y

Dermochelys coriacea. Adult drowned by fishing trawler. Long Reef, NSW. Hal Cogger.

Dermochelys coriacea. Hatchling. Bundaberg, Qld. Hal Cogger.

very dark grey to black above, sometimes with paler marbling, and whitish to pale pink below. Notes: Occurs throughout A ­ ustralian waters, but most sightings are from the heavily

populated east coast. Rarely recorded in NT waters. Vulnerable (IUCN Red List); Endangered (Commonwealth); Critically Endangered (NT).

Side-necked turtles Family Chelidae

and subspecific boundaries and the creation of several new genera and subgenera to house various species. These new names or taxonomic definitions have not always been widely agreed upon, resulting in a multitude of conflicting genus and species names being used in various sources such as journal articles, field guides and databases. Here we have presented names and species in accordance with the ­Australian Society of Herpetologists Official List of ­Australian Species (Australian Society of Herpetologists 2022), with the knowledge that the (relatively) frantic pace of turtle taxonomic work will see these pages outdated before too long. Chelid turtles are also known as ‘sidenecked’ turtles because their head and neck are withdrawn sideways into the shell, rather than straight back. Chelidae can be distinguished from other turtles in the Northern Territory by their having webbed, clawed forelimbs and hindlimbs instead of paddle-shaped flippers. A ­ ustralian sidenecked turtles can be split into two groups in the Northern Territory: the long-necked

Chelidae  – sometimes called Cheluidae in an effort to adhere to the rules of ancient Greek grammar  – contains all the native freshwater turtles of ­Australia, excluding the pig-nosed turtle which is the sole member of Carettochelydidae. Globally, Chelidae are represented by over 60 species of side-necked turtles with webbed, clawed feet that occupy freshwater habitats throughout parts of ­Australia, New Guinea, Indonesia and South America. Although their taxonomy is seemingly in a state of perpetual flux, the current consensus recognises 24 species of A ­ ustralian side-necked turtles in seven genera. Ten species representing four genera occur in the Northern Territory. Side-necked turtles have seen more taxonomic confusion and rearrangement than perhaps any other major ­Australian reptile group. Recent years have seen species names swapped back and forth between turtles, rearrangement of specific 14

Tu r t l e s a n d t o r t o i s e s

turtles, containing one genus (Chelodina) with the head and neck at least as long as the carapace; and the short-necked turtles, containing three genera (Emydura, Elseya and Myuchelys) with much shorter heads and necks. While all side-necked turtles have a bony shell and webbed, clawed feet, they vary considerably in their head and neck morphology. These differences appear to be predominantly driven by differences in diet. Species that consume fruits, such as Elseya, often have massive, robust heads and specialised mouth structures to sheer through tough native fruits. Mature females of some short-necked turtle species sometimes exhibit a condition called macrocephaly, which results in incredible enlargement of the skull and jaw musculature, apparently to facilitate crushing mussel shells. Mostly carnivorous species, such as Chelodina, swallow their prey whole and have not invested in jaws that can sheer through food. Side-necked turtles inhabit a wide variety of freshwater habitats, from coastal floodplains to creeks in sandstone escarpments. In the Northern Territory, they

appear to be active by both day and night. Some Chelodina species occupy ephemeral waterbodies and will burrow and aestivate when wetlands dry out in the dry season. Although basking turtles are a common sight across much of ­Australia, this behaviour is uncommon amongst side-necked turtles in the Northern Territory, presumably because water temperatures are sufficiently high year-round that this risky behaviour is unnecessary. All side-necked turtles are oviparous and most female freshwater turtles lay their eggs on land, usually in sand or soil near water. An exception to this is Chelodina rugosa, which lays its eggs in burrows beneath the water. Freshwater turtles have been harvested for food by Indigenous people in ­Australia for tens of thousands of years and continue to be an important part of the diet and culture of Indigenous people in the Northern Territory. Their cultural and culinary importance to the Indigenous people of the Northern Territory is evidence by their frequent depiction in rock art sites across the Top End.

Key to Chelidae of the Northern Territory 1. Forelimbs each with five claws (A); gular shields entirely separated by the intergular (B)������������������������������������������������������������������������������������������������������������������������������������������������������2 Forelimbs each with four claws (C); gular shields meeting in front of the intergular (D) ��������������������������������������������������������������������������������������������������������������������������������� Chelodina 2. Nuchal shield usually absent (E); skin on temporal region with prominent, low, rounded scales or tubercles������������������������������������������������������������������������������������������������������������������������3 Nuchal shield usually present (F); skin on temporal region smooth, sometimes broken into regular, flat scales or tubercules���������������������������������������������������������������������������������������Emydura 3. Horny shield on top of head not extending down towards the tympanum; neck with distinct but rounded tubercles above�������������������������������������������������������������������������������� Elseya Horny shield on top of head extending down towards the tympanum; neck with distinct, sharp-pointed tubercles above �����������������������������������������������������������������������������Myuchelys 15

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A

B

C

Long-necked and snake-necked turtles genus Chelodina Fitzinger, 1826 Chelodina are a group of 16 ‘long-necked’, freshwater turtles that occur in ­Australia, New Guinea and Indonesia. Eight Chelodina occur in A ­ ustralia, three of which are known to occur in the NT. Chelodina can be distinguished by the following characteristics: smooth head and very elongate neck; no keratinous casque on top of head; gular shields in contact; and four claws on each forefoot. Like many other ­Australian freshwater turtle genera, Chelodina has a tangled taxonomic history. In the last decade, the name applied to the widespread ‘northern snakenecked turtle’ formerly distributed across northern A ­ ustralia has switched between C. rugosa and C. oblonga, due to uncertainty about which species the name C. oblonga should be assigned. Recent work has shown convincingly that the name C.  oblonga applies to the oblong snakenecked turtle of south-western WA, and that the name C. rugosa applies to the snake-necked turtle found in the NT, northern Qld, Torres Straits, and southern New Guinea. To accommodate this change, Chelodina have recently been divided into three sub-genera (Shea et al. 2020), two of which – Chelodina and Chelydera – include

16

D

E

F

freshwater turtles that occur in the NT. Chelodina (Chelodina) Fitzinger, 1826 – the long-necked turtles  – have head and neck lengths equal to or less than their carapace length, broad plastrons and exude an extremely pungent fluid when harassed. In the NT, this subgenus is only represented by Cann’s long-necked turtle (Chelodina (­Chelodina) canni). Chelodina (Chelydera) Thompson & Georges, 2020  – the snakenecked turtles – have head and neck lengths longer than their carapace length, narrow plastrons and exude less pungent fluid when harassed. All other Chelodina in the NT belong to this subgenus. Chelodina (Macrochelodina) Wells & Wellington, 1985 comprises a single species (C. (Macrochelodina) oblonga), which is restricted to south-­ western WA. Some sources elevate these subgenera to full genus status. Although nearly exclusively aquatic, Chelodina are often observed making land-based movements at the onset of the wet season and, occasionally, when waterbodies start to diminish during the dry season. They are almost never observed basking in the NT. Chelodina are primarily carnivorous and feed on a broad range of vertebrate and invertebrate prey, including fish, tadpoles, crustaceans, insects and carrion. Long-necked and snake-necked turtles are ambush hunters and use their long necks to strike out at and suck down prey.

Tu r t l e s a n d t o r t o i s e s

Key to Chelodina of the Northern Territory 1. Head and neck longer than carapace; plastron narrow, not noticeably expanded anteriorly, usually about twice as long as broad (A); intergular usually scarcely longer than the suture between the pectorals (B)������������������������������������������������������������������������������������������������������2 Head and neck not longer than carapace; plastron greatly expanded anteriorly, usually only about 1.5 times as long as it is broad (C); intergular usually at least twice as long as the suture between the pectorals (D)����������������������������������������������������������������������������������������C. canni 2. Head much wider than the neck; conspicuous chin barbels with multiple barbels along each jaw ������������������������������������������������������������������������������������������������������������������������������C. burrungandjii Head not much wider than the neck; at most two small barbels on the chin���������� C. rugosa

A

B

C

D

Sandstone snakenecked turtle

Chelodina (Chelydera) burrungandjii Thomson, Kennett & Georges, 2000 CL 316 mm. A moderately sized Chelodina with a very long, slender neck; large, wide, strongly depressed head; and short face. Carapace dark brown to black, and oval-shaped with slightly upturned lateral edges. Plastron narrow anteriorly, usually about twice as long as broad, and cream. Head noticeably wider than neck and with dark variegations on head and neck. Chin and jaw usually with multiple, conspicuous barbels. Notes: Occurs in two disjunct regions, one in the Top End, NT; the other through the Kimberley region, WA, and adjoining NT. The Top End population is restricted to permanent creeks, rivers and billabongs associated with the sandstone escarpments and gorges

Chelodina (Chelydera) burrungandjii. Arnhem Plateau, NT. Etienne Littlefair.

of the Arnhem Plateau, NT. The western population inhabits various freshwater waterways through the Kimberley, WA, and north-western NT. Unlike other Chelodina, they appear to consume some plant matter. Taxonomic notes: Some sources recognise two poorly defined subspecies (with other sources elevating them both to full species): C. b. burrungandjii Thomson, 17

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Kennett & Georges, 2000 in the Top End, NT; and C. b. walloyarrina McCord & Joseph-Ouni, 2007 in the Kimberley, WA, and north-western NT. However, as the evidence suggests the genetic divergence between these disjunct populations is insignificant, we treat them here as a single species. Similar species: C. rugosa

Northern snakenecked turtle

Chelodina (Chelydera) rugosa Ogilby, 1889

CL 260  mm. A moderately sized Chelodina with a relatively short neck and broad head. Carapace reddish brown to black, and broad and roundish in shape. Plastron broad anteriorly and usually only about 1.5 times as long as it is broad. Plastron cream to yellowish brown with some sutures narrowly marked with black. Head, neck, and limbs may be flushed with pink, especially on juveniles. Notes: Occurs in disjunct populations through eastern Qld and throughout the Gulf of Carpentaria region, from about Weipa, Qld to southern Top End, NT. In the NT, occurs in fresh waterways of the Gulf region, west to Mataranka and south to the Daly Waters region. Mostly inhabits billabongs and swamps. Taxonomic notes: Some sources recognised two poorly defined subspecies; however, we consider the name Chelodina canni rankini Wells, 2007 to be a nomen nudum and therefore unavailable.

CL 360  mm. A large Chelodina with a very long, thick neck; and relatively narrow head. Carapace brown to black, and oval shaped. Plastron narrow anteriorly, usually about twice as long as broad, and cream to reddish brown. Head not noticeably wider than neck, often with dark variegations. Chin with at most two small barbels. Notes: Occurs through ­northern ­Australia, Torres Strait islands and southern New Guinea, from Cape York Peninsula through the Top End, NT. In the NT, occurs through the Gulf of Carpentaria and Top End. Also occurs on several islands, including the Tiwi Islands, Groote Eylandt and Croker Island. Inhabits floodplains, creeks and large rivers subject to extensive wet season flooding. Eggs are laid underwater and remain dormant until water levels drop. Taxonomic notes: Some sources recognise C. rugosa as being split into two poorly defined species: C.  kurrichalpongo Joseph-Ouni, McCord, Cann & Smales, 2019 in the Top End, NT; and C. rugosa Ogilby, 1889 in Qld, Torres Strait and New Guinea. While some genetic evidence suggests that NT populations may be taxonomically distinct from the type population in Cape York, Qld, the ­Australian Society of Herpetologists Official List of ­ Australian

Chelodina (Chelodina) canni. Daly Waters, NT. Brendan Schembri.

Chelodina (Chelydera) rugosa. Adelaide River region, NT. Etienne Littlefair.

Cann’s long-necked turtle Chelodina (Chelodina) canni McCord & Thomson, 2002

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Tu r t l e s a n d t o r t o i s e s

Species (Australian Society of Herpetologists 2022) does not consider the name provided by Joseph-Ouni et  al. 2019 to be available

according to their criteria and, as such, we treat C.  rugosus as a single species. Similar species: C. burrungandjii

Snapping turtles genus Elseya Gray, 1867

contact, instead separated by intergular shield; nuchal shield usually absent; head with horny shield not extending down towards the tympanum; neck with distinct but rounded tubercles above; and five claws on each forefoot. Snapping turtles typically inhabit deep, permanent pools associated with rivers and their tributaries and rarely leave the water other than to occasionally bask and for females to nest. Snapping turtles are largely herbivorous and feed on fruits, particularly pandanus nuts, and other vegetation but will also consume some animal material.

Snapping turtles are a group of nine large, robust, short-necked, freshwater turtle species that occur in ­Australia, New Guinea and Indonesia. Five snapping turtle species occur in ­Australia, three of which occur in the NT. Elseya can be distinguished by the following characteristics: head and neck much shorter than shell length; keratinous casque on top of head that does not extend down towards tympanum; skin on temporal region with prominent, low, rounded scales or tubercles; gular shields not in

Key to Elseya of the Northern Territory 1. Plastron dark, or pale with dark markings ����������������������������������������������������������������������������������������������������������������������������������������������������������� 2 Plastron pale and patternless����������������������������������������������������������������������������������������E. flaviventralis 2. Intergular deeply separates humerals, at least by half (A); head shield extensive and robust, extending forward to cover the dorsal surface of the head between the eyes; patterning of temporal and head region not reticulate��������������������������������������������������������������������������������� E. dentata Intergular moderately separates humerals, at most by half (B); head shield modest, typically not extending forward to cover the dorsal surface of the head between the eyes; patterning of temporal and head region reticulate ��������������������������������������������E. lavarackorum

A

B

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Northern snapping turtle

Elseya dentata Gray, 1863 CL 330  mm. A moderately large snapping turtle with a brown to dark brown, broadly oval-shaped and posteriorly expanded carapace. Juveniles with strongly serrated carapace. Plastron creamish to brown, usually with dark markings, and with intergular deeply separating humerals. Head and temporal region without reticulated pattern. Head shield extensive and robust, extending forward to cover the dorsal surface of the head between the eyes. Neck with numerous rounded tubercles. Notes: Occurs through northern and eastern Kimberley, WA and the Victoria River region, western Top End and western Gulf of Carpentaria, NT. Appears to occur in two disjunct populations in the NT. The western population occurs through the Victoria River, Daly River and Finniss River Basins and the eastern population occurs through the Roper and Limmen Bight River basins. Inhabits permanent rivers and their tributaries. Taxonomic notes: Elseya dentata appears to be a species complex requiring detailed genetic and morphological work to resolve. Similar species: E. flaviventralis; E. lavarackorum

Yellow-bellied snapping turtle

Elseya flaviventralis Thompson & Georges, 2016 CL 340 mm. A large snapping turtle with a brown to dark brown, roughly oval-shaped, and anteriorly narrowed and rounded carapace. Juveniles with serrated carapace. Plastron cream without dark markings. Head relatively narrow with two barbels on lower jaw. Head and neck often with clean delineation between dark, greyish dorsal and cream ventral colour. Notes: Endemic to the NT. Occurs through northern Top End, NT in river systems associated with the Arnhem Plateau, including the Mary, South Alligator, East Alligator, Goyder and Mann rivers. Also recorded from the Cato River in North East Arnhem Land. Typically inhabits deep, permanent pools associated with rivers through and connected to the Arnhem Plateau. Taxonomic notes: Some sources refer to this species as E.  jukesi Wells, 2002. Similar species: E. ­dentata; E. lavarackorum

Elseya flaviventralis. Arnhem Plateau, NT. Etienne Littlefair.

Elseya dentata. Reynolds River, NT. Etienne Littlefair.

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Tu r t l e s a n d t o r t o i s e s

Gulf snapping turtle Elseya lavarackorum (White & Archer, 1994)

CL 350  mm. A large snapping turtle with a brown to black, broadly oval-shaped and anteriorly blunt carapace. Juveniles with strongly serrated carapace. Plastron creamish to brown, usually with dark markings, often fading with age, and intergular moderately separating humerals. Large, robust head and neck brown– grey, fading to light grey with age, head and temporal region usually with reticulated pattern. Head shield modest, typically not extending forward to cover the dorsal surface of the head between the eyes. Chin with 1–2 barbels. Neck with low, blunt tubercles. Notes: Occurs in some rivers outflowing into the Gulf of Carpentaria in Qld and NT. Thought to occur from the G ­ regory– Nicholson River drainages in north-western Qld to the Calvert, NT. Recent genetic evidence has demonstrated this species also occurs in at least the Roper River, NT (Georges et  al. 2021), but may also inhabit other drainages outflowing into the Gulf of Carpentaria, NT. Inhabits deep, permanent, pandanus-lined pools in upper reaches of spring-fed rivers, and large, permanent rivers. Least Concern (NT); Endangered (Commonwealth). Taxonomic notes: Originally described as Emydura lavarackorum from a Pleistocene fossil from Riversleigh, Qld. These fossils

Short-necked turtles genus Emydura Bonaparte, 1836 Short-necked turtles are a group of five moderate to large, short-necked, freshwater turtle species that occur in ­Australia and New Guinea. Four short-necked turtle species occur in ­Australia, three of which are known to occur in the NT. Emydura can be distinguished by the following characteristics: head and neck much shorter than shell length; no keratinous casque on top of head; neck generally smooth, but may have small bumps; skin on temporal region

Elseya lavarackorum. Lawn Hill Creek, Qld. Etienne Littlefair.

were subsequently found to match living turtles in the Gregory–Nicholson drainages (Thomson et al. 1997). Recent work based on shell scutellation differences suggested that the living specimens differ enough from the fossil specimens of Elseya lavarackorum to be regarded as separate species – Elseya oneiros (Joseph-Ouni et al. 2020). However, because this description failed to account for the extent of variation in scutellation characteristics of fossil and living specimens, E. oneiros was deemed to be a junior synonym of E. lavarackorum (Turtle Taxonomy Working Group 2021). Additionally, the ­Australian Society of Herpetologists Official List of A ­ ustralian Species (Australian Society of Herpetologists 2022) does not consider the name provided by Joseph-Ouni et  al. 2020 to be available. Similar species: E. dentata; E. flaviventralis

smooth, sometimes broken into regular, flat scales or tubercules; gular shields not in contact, instead separated by intergular shield; nuchal shield usually present; and five claws on each forefoot. Some of northern A ­ustralia’s shortnecked turtles can be very tricky to distinguish from one another in the field. Although the true distribution of the Emydura spp. of the NT continues to be unclear, it appears that the distributions of a few species overlap (E. tanybaraga, E. subglobosa worrelli and E. victoriae). At the very least, 21

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these three species all appear to occur in the Daly River drainage, meaning distribution cannot be reliably used to distinguish them. Unfortunately, there are currently no consistent colour pattern or morphological differences between at least two of these species (E. tanybaraga and E. subglobosa worrelli) that are supported by genetic evidence and readily diagnosable in the field. Short-necked turtles inhabit a range of permanent and ephemeral waterways,

including creeks, rivers, floodplains and  billabongs. Although infrequently observed basking in the Top End, species that inhabit ephemeral waterholes are occasionally observed making land-based movements as waterholes shrink during the dry season or as they expand in the wet season. Short-necked turtles are omnivorous and feed on aquatic plants, fallen fruits, invertebrates, small vertebrates and carrion.

Key to Emydura of the Northern Territory 1. Eye with dark streak or dot beyond and/or before pupil������������������������������������������������������������������2 Eye with no dark streak or dots before or after pupil ����������������������������������������������������E. victoriae 2. Eye usually with dark streak running back from or through pupil, often faint; coloured face stripe usually yellowish and not dark edged*����������������������������������������������������E. tanybaraga Eye usually with two dark dots, one in front of and one behind pupil; coloured face stripe yellowish, pinkish and/or salmon and usually dark edged*������������������E. subglobosa worrelli *

Emydura subglobosa worrelli and E. tanybaraga are not readily distinguishable in the field and the features provided here should only be used as a guide.

Worrell’s turtle

Emydura subglobosa worrelli Wells & Wellington, 1985 CL 260  mm. A moderately sized short-necked turtle with pale green to yellow iris and a distinctive black dot before and after pupil. Carapace greyish to brownish and broadly oval and expanded posteriorly. Juveniles with serrated carapace. Plastron creamish. Head usually with a prominent yellowish, pinkish and/or salmon stripe from snout, above eye, to above ear, often with another yellowish, pinkish and/or salmon stripe running along jaw and neck. Facial stripes are usually dark-edged. With age, facial stripes less prominent, and head sometimes becomes greatly enlarged 22

Emydura subglobosa worrelli. Southern Arnhem Land, NT. Stephen Zozaya.

(macrocephaly). Subspecies: Two subspecies; only E. s. worrelli occurs in the NT. Emydura s. subglobosa (Krefft, 1876) occurs on the tip of Cape York Peninsula, Qld and through southern New Guinea. Notes: Distribution unclear. Appears to occur from Katherine River, NT, south-east to the Flinders River in

Tu r t l e s a n d t o r t o i s e s

north-western Qld. In the NT, occurs at least to the southern Daly River drainage (­K atherine River), but it is currently unclear how far north it occurs. Inhabits creeks, rivers and billabongs. Taxonomic notes: Some sources recognise E. s. subglobosa and E. s. w ­ orrelli as two distinct species (see Cann and Sadlier 2018); however, evidence suggests the genetic divergence between these subspecies is insignificant, and we treat them here as a single species following the ­Australian Society of Herpetologists Official List of ­ Australian Species (­Australian Society of Herpetologists 2022). Similar species: E. tanybaraga; E. victoriae

southern Cape York Peninsula, Qld, and northern Top End, NT. In the NT, appears to occur from the Daly River drainage, across the northern Top End to North East Arnhem Land. Inhabits permanent and ephemeral waterways, including creeks, rivers, floodplains and billabongs. Similar species: E. subglobosa worrelli; E. victoriae

Northern yellowfaced turtle

CL 285  mm. A moderately large short-necked turtle with yellow iris and usually a dark streak running back from or through pupil, sometimes faint. Carapace fawn to dark greyish brown, often with dark markings, and broadly oval and expanded posteriorly. Juveniles with serrated carapace. Plastron creamish. Head usually with a prominent yellowish stripe from snout, above eye, to above ear, often with another yellowish stripe running along jaw and neck. Facial stripes are not distinctly dark-edged. With age, facial stripes may fade, and head sometimes becomes greatly enlarged (macrocephaly). Notes: Occurs through western and

CL 250  mm. A moderately sized short-necked turtle with golden orange iris and no dark markings before or after pupil. Carapace usually brownish, sometimes with dark flecks. Posterior of carapace is noticeably wider than anterior and posterior edge is usually serrated. Juveniles with serrated carapace. Plastron whitish with pink flush. Head with a prominent reddish stripe from eye, sometimes from snout, across temporal region, often with another pale red stripe running from gape of mouth and along neck. With age, facial stripes fade, and head often becomes greatly enlarged (macrocephaly). Notes: Occurs through the Kimberley, WA and north-western NT. In the NT, occurs through the Victoria and Daly River drainages. Inhabits riverine pools which become still and isolated during the dry season. Taxonomic notes: Some sources recognise E. victoriae and

Emydura tanybaraga. Berry Creek, NT. Etienne Littlefair.

Emydura victoriae. Bullo River, NT. Hal Cogger.

Emydura tanybaraga Cann, 1997

Northern red-faced turtle

Emydura victoriae (Gray, 1842)

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E. australis (Gray, 1841) as distinct species; however, E. australis appears to be a junior synonym of Emydura macquarii (Gray, 1830) and has been considered a nomen dubium by the ­Australian

Society of Herpetologists Official List of ­Australian Species (­ Australian Society of Herpetologists 2022). Similar species: E. subglobosa worrelli; E. tanybaraga

Helmeted turtles genus Myuchelys Thompson & Georges, 2009

Saw-shelled turtle

Helmeted turtles are a group of four moderate to large, short-necked, freshwater turtle species that occur through eastern and northern A ­ ustralia. Only a single species occurs in the NT. Myuchelys can be distinguished by the following characteristics: head and neck much shorter than shell length; skin on temporal region with prominent, low, rounded scales or tubercles; keratinous shield on head that extends down towards tympanum; neck dorsum with distinct, sharp-pointed tubercles; gular shields not in contact, instead separated by intergular shield; nuchal shield usually absent; head with horny shield extending down towards the tympanum; and five claws on each forefoot. There is some debate surrounding what generic name to use for helmeted turtles. Some sources consider Myuchelys ­Thompson & Georges, 2009 to be invalid and instead use the earlier name Wollumbinia Wells, 2007. However, following Kaiser et al. (2013), the ­Australian Society of Herpetologists Official List of ­ Australian Species (­Australian Society of Herpetologists 2022) considered the generic name Wollumbinia unavailable and rejected its use in favour of Myuchelys. Other than Myuchelys latisternum, Myuchelys spp. are some of the most threatened freshwater turtles in ­Australia. One species (M. georgesi) has recently suffered rapid and catastrophic population declines due to a viral disease that nearly wiped out the entire species.

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Myuchelys latisternum Gray, 1867 CL 249 mm. A large helmeted turtle with brown to blackish brown carapace usually prominently serrated on rear edge. Juveniles with high central keel and strongly serrated carapace. With age, carapace tends to flatten and serrations reduce or disappear. Plastron cream to yellow. Head grey–brown with horny casque extending down to tympanum. Lacks coloured facial stripes. Neck with many spinous tubercles and often clean delineation between dark, greyish dorsal and cream ventral colour. Iris colour variable, but usually with dark dot before and after pupil. Notes: Occurs throughout north-eastern A ­ ustralia, from Richmond drainage, NSW, north to the tip of Cape York, Qld. Occurs in a number of disjunct populations west of the Great Dividing Range, including the Gregory and Nicholson rivers drainage in north-western Qld and in rivers associated with the Arnhem Plateau, NT. In the NT, recorded from the headwaters

Myuchelys latisternum. Arnhem Plateau, NT. Etienne Littlefair.

Tu r t l e s a n d t o r t o i s e s

of the Liverpool, Mann, Mary and South and East Alligator rivers. A single additional record exists from the headwaters of the Limmen Bight River. In the NT, typically inhabits lagoons, creeks and upper reaches of large

rivers flowing through sandstone escarpment. Broadly omnivorous and feeds on aquatic invertebrates, small vertebrates and aquatic plants. Apparently capable of consuming cane toads without ill-effect.

Pig-nosed turtle Family Carettochelydidae

Territory. In New Guinea, the species gets almost twice this size. Pig-nosed turtles primarily feed on aquatic vegetation, such as ribbon weed, and fallen fruits, but will also consume crustaceans, aquatic and terrestrial invertebrates, molluscs and carrion. They actively forage by both day and night. Female pig-nosed turtles lay clutches of 7–19 eggs on sandy riverbanks during the dry season. The eggs develop but do not hatch until rising water or heavy rainfall floods nests and triggers mass, synchronised hatching. The sex of hatchlings is determined by nest temperature during early development, with nesting location and time of laying during the dry season affecting the nest temperature and thus sex ratio of hatchlings. Pig-nosed turtles appear to have indirectly benefited from the arrival of cane toads in A ­ ustralia. Cane toads have caused significant declines in yellow-spotted monitors (Varanus panoptes), a major turtle nest predator, which has resulted dramatic reduction in the number of nests depredated by goannas.

Genus Carettochelys Ramsay, 1886 Carettochelydidae has been around for at least 40 million years and appears to have once been widespread through North America, Europe, Central Asia and Sarawak, but is now only represented by Carettochelys, the sole genus in the family, containing a single extant species. This large, distinctive turtle is found in large, freshwater river systems of the Northern Territory and in freshwater and brackish rivers through southern New Guinea. It is unclear whether these turtles venture into the brackish reaches of northern A ­ ustralian rivers. Presumably recent immigrants to A ­ ustralia, Carettochelys turtles are thought to have emigrated from New Guinea when these landmasses were joined. Pig-nosed turtles are not closely related to other ­Australian freshwater turtles and are unique and highly distinctive in appearance. Carettochelys can be distinguished by its forelimbs that are modified into paddle-like flippers, each with two claws on the anterior edge and a shell covered by soft skin rather than hard shields. Their common name is derived from the fleshy, tubular, trunk-like proboscis. Pig-nosed turtles are considerably larger than other Australian freshwater turtles, with large ­ adults weighing up to 10 kg in the Northern

Pig-nosed turtle

Carettochelys insculpta Ramsay, 1886 CL 400–550 mm. A very large freshwater turtle with shell covered by soft skin. Unique among ­ Australia’s freshwater turtles in having the forelimbs

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modified into flippers, each with two claws on the anterior edge. Greyish to grey–brown above and whitish below. Head with white spots behind eyes. Snout formed into a fleshy, tubular, pig-like proboscis. Notes: In ­Australia, endemic to the NT. Only known from the Daly and Alligator River systems of the western Top End, NT. Inhabits large, freshwater rivers with sandy bottoms and banks. Near Threatened (NT); Vulnerable (IUCN Red List). Carettochelys insculpta. Daly River, NT. Brendan Schembri.

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Lizards (Order Squamata, Suborder Lacertilia) Lizards are an incredibly diverse, paraphyletic group of squamate reptiles. While we now know that snakes evolved from lizards (meaning that snakes are actually just limbless lizards), this guide treats these two groups separately for convenience. Lizards have a near-global distribution and

are found on every continent except Antarctica. Early lizards were first observed in the fossil records about 200 million years ago. They have since diversified into nearly 6000 species across the globe. A ­ ustralia is home to seven lizard families: southern padless geckos (Carphodactylidae), ­Austral

Head of a typical skink (Ctenotus robustus) showing the position and name of head scales from a dorsal, ventral and lateral perspective.

Lizard body measuring points and some key features. 27

F i e l d G u i d e t o t h e R e p t i l e s o f t h e N o r t h e r n Te r r i t o r y

Names and locations of body stripes and zone that compose the body colour pattern of a typical skink (Ctenotus robustus).

Condition of lower eyelids in skinks: (A) moveable and scaly (Ctenotus robustus); (B) movable with transparent palpebral disc (Carlia sexdentata); and (C) immovable with a fixed transparent spectacle (Cryptoblepharus juno).

geckos (Diplodactylidae), typical geckos (Gekkonidae), legless lizards (Pygopodidae), skinks (Scincidae), dragons (Agamidae) and monitors (Varanidae). All seven of these families are represented in the Northern Territory. Lizards are exceptionally diverse in their morphology, physiology, life history and behaviour. In the Northern Territory, they vary from tiny fossorial, limb-reduced skinks to arboreal geckos with adhesive toepads, to giant, terrestrial monitor lizards. Most lizards are immediately 28

recognisable as such and are easily distinguished from other ­Australian reptiles by typically possessing limbs (cf. snakes) and lacking external shells or bony dermal plates (cf. turtles and crocodiles). Trouble arises, however, when attempting to distinguish limbless lizards from snakes. Limblessness or near limblessness has evolved independently several times in A ­ ustralian lizards, with one family (Pygopodidae) being entirely limbless. Limbless lizards are distinguished from snakes by possessing external ear openings and fleshy tongues.

Lizards

Key to lizard families of the Northern Territory 1. Limbs present, although they are sometimes reduced to no more than a stump; if hindlimbs are reduced to stumps with no digits, lower eyelids are moveable ������������������������2 Limbs reduced to a scaly flap on either side of the vent (A); eyes covered by fixed, transparent spectacles�������������������������������������������������������������������������Pygopodidae (legless lizards) 2. Dorsal scales juxtaposed (non-overlapping) and eyes without movable eyelids; tongue not deeply forked �������������������������������������������������������������������������������������������������������������������������������������������3 Dorsal scales imbricate (overlapping) and eyes usually with moveable eyelids; if dorsal scales juxtaposed, eyelids moveable and tongue deeply forked �������������������������������������������������6 3. Digits flat, usually entirely in contact with substrate when viewed laterally (B); if present, terminal claw small and located in a groove between distal subdigital lamellae (C) or protruding from the dorsal surface of a large, expanded toe pad (D)������������������������������������������4 Digits bent or angular when viewed laterally (E); distinct terminal claw not located in a groove or above a large, expanded toe pad (E)������������������������������������������������������������������������������������5

A

B

C

D

E

F

G

H

I

J

K

L

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4. Ventral surface of digits with undifferentiated tubercles (F), enlarged subdigital lamellae in a continuous parallel series (G), or with an enlarged distal pair of subdigital plates (H), which may be continuous with (G), or separated from (H), remaining subdigital lamellae; if enlarged subdigital lamellae in a continuous parallel series (I), also with lamellae under tip of tail; dorsal digit scales above expanded toe pad not distinctly larger than basal dorsal digit scales (J) �����������������������������������������������������������������������������������Diplodactylidae (Austral geckos) Ventral surface of digits with a continuous series of enlarged subdigital lamellae but lacking a distinctly enlarged pair of distal plates (K); no lamellae under tip of tail; enlarged dorsal scales above expanded toe pads are significantly larger than basal dorsal digit scales (L; part) ����������������������������������������������������������������������������������������������������������������������������Gekkonidae 5. Postmental scales and adjacent gular scales of near equal size (M); original tail with spinose tubercles ���������������������������������������������������Carphodactylidae (southern padless geckos) Postmental scales distinctly enlarged (N); tail without large spinous tubercles (part) ������������������������������������������������������������������������������������������������������������������������Gekkonidae (typical geckos) 6. Dorsal head scales very small and irregularly arranged (O, P)���������������������������������������������������������7 Dorsal head covered in enlarged, regular and usually symmetrical shield-like scales (Q) ��������������������������������������������������������������������������������������������������������������������������������������������� Scincidae (skinks) 7. Broad, flat, fleshy tongue, which is neither sheathed at its base nor deeply forked, with no more than slight notch at tip (R)�������������������������������������������������������������������������Agamidae (dragons) Long, slender, deeply forked tongue, which is sheathed at its base (S)��������������������Varanidae (monitors)

N

M

Q

30

R

O

S

P

Lizards

Southern padless geckos Family Carphodactylidae Southern padless geckos (Carphodactylidae) are a group of large, distinctive geckos found across much of mainland ­Australia. Carphodactylidae is the only reptile family that is endemic to A ­ ustralia. Currently, there are 32 species of carphodactylid geckos in seven genera recognised in ­Australia. Only five carphodactylid species in two genera (Nephrurus and Underwoodisaurus) occur in the Northern Territory. Most of these species (except Nephrurus sheai) are restricted to the semi-arid and arid southern half of the Territory. Like most A ­ustralian geckos (infraorder ­ Gekkota: Carphodactylidae; Diplodactylidae; Gekkonidae; and Pygopodidae), they lack eyelids, have the ability to vocalise and lay two eggs (some Gehyra only lay a single egg). Carphodactylid geckos can be broadly split into three morphological groups. Although not present in the Northern Territory, the leaf-tailed geckos (Orraya, Phyllurus and Saltuarius) are a distinctive group of geckos with broad, flattened, leaflike tails. The leaf-tailed geckos are restricted to the forests of eastern ­Australia.

The knob-tailed geckos (Nephrurus) are a group of massive, large-headed geckos, including the heaviest bodied geckos in Australia. As their name suggests, they ­ have a small terminal knob on their tails. Currently, the function of this knob, if it has one, is unknown. Knob-tailed geckos are most abundant and diverse in arid ­Australia and comprise most of the carphodactylids in the Northern Territory. The carrot-tailed geckos (Carphdactylus, Underwoodisaurus and Uvidicolus) all have comparatively long tails that are constricted at the base before widening and gradually becoming narrower before terminating in a slender blunt point. Carphodactylid geckos can be distinguished from other lizards in the Northern Territory by the presence of limbs; lack of movable eyelids; non-overlapping dorsal scales; broad, fleshy tongue; non-flattened digits; distinct terminal claw not located in a groove or above a large, expanded toe pad; postmental scales and adjacent gular scales of near equal size; and original tail with spinose tubercles. Because of their distinctive appearance and lack of diversity, carphodactylid geckos are fairly easy to distinguish from similar sympatric lizards in the Northern Territory.

Key to Carphodactylidae of the Northern Territory 1. Original tail terminates in a small, distinctive knob (A); more than 16 supralabial scales, each of which is small and only slightly larger than adjacent granular scales ������������������ Nephrurus Original tail carrot-shaped and terminating in a slender, blunt point; fewer than 16 supralabial scales, each of which is enlarged and distinctly larger than adjacent granular scales���������������������������� ���������������������������������������������������������������������������������������� Underwoodisaurus

A

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Knob-tailed geckos genus Nephrurus Günther, 1876 A group of nine large, robust gecko species with large, deep heads, slender limbs, short, clawed, padless digits and small, spinous subdigital lamellae. Four of these species are recorded in the NT. Nephrurus can be distinguished from other carphodactylids by the following characteristics: original tails terminate in a small, distinctive knob; and more than 16 supralabial scales, each of which is small and only slightly larger than adjacent granular scales. Nephrurus are ground-dwelling geckos. In the NT, Nephrurus fall into two groups that differ in morphology and habitat association: the smooth knob-tailed geckos (N.  laevissimus and levis), which

are adorned with only small, single scale dorsal tubercles, and are associated with sandplains and dunefields; and the rough knob-tailed geckos (N. amyae and shaei), which are adorned with large tubercles composed of multiple conical spines, and are associated with rocky habitats. Smooth knob-tailed geckos excavate their own burrows, while rough knob-tailed geckos tend to shelter under rocks and in crevices. Rough-knob tailed geckos are the only geckos that have lost the ability to autonomise their tails. When harassed or threatened, Nephrurus raise and inflate their bodies, gape and lunge at the aggressor while uttering a wheezing bark. Carnivorous, mostly consuming arthropods but will also take small vertebrates, such as other geckos.

Key to Nephrurus occurring in the Northern Territory 1. Scattered tubercles on flanks���������������������������������������������������������������������������������������������������������������������2 Smooth flanks, without tubercles�����������������������������������������������������������������������������������N. laevissimus 2. Complex tubercles composed of multiple conical scales (A); tail small, shrivelled and spiny (B)���������������������������������������������������������������������������������������������������������������������������������������������������������������3 Simple dorsal tubercles composed of a single conical scale (C); tail comparatively broad and flat (D)���������������������������������������������������������������������������������������������������������������������������������������������N. levis 3. Digits without bands; tubercles heavily spinous; occurs in the arid central NT������� N. amyae Digits strongly banded; tubercles moderately spinous; occurs in northern NT �������� N. sheai A

32

B

C

D

Lizards

Centralian knobtailed gecko

Pale knob-tailed gecko

SVL 135 mm. A ­ ustralia’s most massive gecko. A large, robust Nephrurus adorned with complex tubercles composed of multiple conical scales, the largest and most spinous on rump and thighs; small, shrivelled, spiny tail; and lacking banded digits. Dorsal colouration rich reddish brown with broad, dark transverse band on nape and fine, dark transverse lines alternating with rows of paler bands or spots, with each pale spot centred on a spinous tubercle. Flanks are tan brown with numerous rosettes of pale, spinous tubercles. Limbs long and slender, lacking irregular crossbands distally and with enlarged tubercles on dorsal surface. Large head patterned with a fine dark and broader pale reticulum. Tail short and spinous, terminating in a globular, kidney-shaped knob. Ventral surface pale. Notes: Occurs in the rocky ranges of arid central NT. Known outside of the NT from only a single record collected near Warburton, WA. Predominantly associated with the rocky areas of the MacDonnell Ranges and Burt Plain bioregions; however, recent, unconfirmed records suggest N. amyae may occur in areas of the Tanami. Inhabits rocky slopes and outcrops vegetated by spinifex. Shelters beneath or between rocky boulders. Similar species: N. sheai

SVL 93  mm. Smallish, with smooth flanks, lacking tubercles. Dorsal colouration pinkish, yellowish to orangish brown with or without scattered white dorsal dots. Dorsal body pattern includes broad, dark lines and/or blotches, the most prominent of which are from behind eyes and across base of head, across nape, curving longitudinally from each shoulder and above each hip. Sharp demarcation between darker dorsal and white ventral colour on flanks. Limbs long and relatively robust, lacking tubercles and typically patternless. Head large, patterned with dark blotches and stripes, with pale supraoculars. Tail short with white dorsal tubercles, terminating in a smooth, globular, kidney-shaped knob. Ventral

Nephrurus amyae Couper, 1994

Nephrurus amyae. Watarrka National Park, NT. Brendan Schembri.

Nephrurus laevissimus Mertens, 1958

Nephrurus laevissimus. Yulara, NT. Brendan Schembri.

Nephrurus laevissimus. Yulara, NT. Chris Jolly. 33

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surface immaculate white. Notes: Occurs throughout the western deserts of WA, SA and NT. Restricted to the arid, sandy south-western corner of the NT, north almost to Tanami and east to near Finke. Inhabits desert dunefields vegetated with spinifex. Excavates and shelters in burrows. Similar species: N. levis levis

Smooth knob-tailed gecko Nephrurus levis De Vis, 1886

SVL 102 mm. A medium-sized Nephrurus with simple dorsal tubercles composed of a single conical scale; and broad, dorsally depressed, fleshy tail. In the NT, dorsal colouration pale orangish brown to dark purplish brown with numerous small, scattered tubercles. Dorsal body pattern typically includes narrow, pale lines across base of head, across the neck and curving from forelimbs across back, each of which is dark-edged or with dark, purplish brown interspacing. Dorsum with white tubercles, scattered or arranged in irregular cross bands. Demarcation between darker dorsal and white ventral colour on flanks is distinct. Limbs long and relatively robust, typically scattered with fine white tubercles. Head large, patterned with dark and pale blotches, with pale supraoculars. Tail relatively broad and robust with longitudinal rows of dorsal tubercles, terminating in a smooth, globular, kidneyshaped knob. Ventral surface immaculate white. Subspecies: Three subspecies; only Nephrurus l. levis De Vis, 1886 occurs in the NT. Nephrurus l. occidentalis Storr, 1968 and N. l. pilbarenis Storr, 1968 are restricted to WA. Notes: Occurs

Nephrurus levis levis. Yulara, NT. Chris Jolly. 34

throughout the arid interior of ­ Australia. Nephrurus l. levis is mostly restricted to the arid, southern half of the NT; however, some verified records exist from semi-arid areas nearly on the latitude of Elliott. Inhabits a variety of sandy soiled habitats from sandplain to desert dunefields. Excavates and shelters in burrows. Similar species: N. laevissimus

Northern knob-tailed gecko Nephrurus sheai Couper, 1994

SVL 120  mm. A large, robust Nephrurus adorned with complex tubercles composed of multiple conical scales, the largest and most spinous on rump and thighs; small, shrivelled, spiny tail; and digits strongly banded with brown and white. Dorsal colouration tan, greyish brown to reddish brown with broad, dark transverse band on nape. Pale dorsal crossbands range from distinct to obscure and are continuous or broken into a series of spots, with each pale spot centred on a spinous tubercle. Fine dark lines between pale cross bands sometimes form a reticulated pattern. Lateral zones are tan brown with numerous rosettes of pale, spinous tubercles. Limbs long and slender, often with irregular crossbands distally and with enlarged tubercles on dorsal surface. Large tan head patterned with a fine dark and broader pale reticulum. Tail short and spinous, terminating in a globular, kidneyshaped knob. Ventral surface cream sometimes faintly marbled with grey or brown. Notes:

Nephrurus sheai. Keep River National Park, NT. Chris Jolly.

Lizards

Occurs throughout rocky ranges of the central Top End and Ord–­Victoria River region, NT and Kimberley, WA. In the NT, N. sheai occurs in two apparently isolated populations; one is associated with the western and northern edges of the Arnhem Plateau and the other is associated

with rocky ranges predominantly south-west of the ­Victoria River, with a few records from the Bradshaw area. Inhabits rocky outcrops in tropical, open woodland, often vegetated by spinifex or other grasses. Shelters beneath or between rocky boulders. Similar species: N. amyae

Thick-tailed geckos genus Underwoodisaurus Wermuth, 1965 Two large, robust gecko species with large, deep heads, slender limbs, short, clawed, padless digits and small, transverse subdigital lamellae. Only one of two thicktailed gecko species occurs in the NT. Underwoodisaurus can be distinguished from other carphodactylids by the following characteristics: tails are carrotshaped, terminating in a slender, blunt point; fewer than 16 supralabial scales, each of which is enlarged and distinctly larger than adjacent granular scales. Underwoodisaurus are ground-dwelling geckos. Although broadly distributed and associated with a variety of habitats across southern ­Australia, thick-tailed geckos are relatively restricted in their distribution and habitat association in the NT. When harassed or threatened, Underwoodisaurus raise and inflate their bodies, gape and lunge at the aggressor while uttering a wheezing bark. Because of this behaviour, they are also known by the common name ‘barking geckos’. Carnivorous, mostly consuming arthropods but will also take small vertebrates, such as other geckos.

Thick-tailed gecko

Underwoodisaurus milii (Bory de Saint-Vincent, 1825)

Underwoodisaurus milii. Coober Pedy, SA. Chris Jolly.

fewer than 16 supralabial scales. Dorsal colouration pink to dark purplish brown with numerous scattered, small white or yellow dots, each centred on a tubercles and tending to form transverse bands across back, interspersed with tiny blackish dots. Yellow spots on nape and back of head bold and tending to form broader, discontinuous pale, curved bands. Limbs long and slender, often with numerous scattered, small white dots centred on tubercles. Head large, patterned with diffuse, light patches. Original carrot-shaped, tail spinous, dark with five or six white bands. Regenerated tail smooth, blunt and mottled. Ventral surface whiteish. Notes: Occurs throughout southern mainland ­Australia. In the NT, U. milli are uncommon and appear to be restricted to arid, rocky plains of the Finke bioregion and the MacDonnell Ranges. Inhabits rocky screes and outcrops vegetated by spinifex. Shelters beneath or between rocky boulders. Often emerges late at night.

SVL 100  mm. A large, robust gecko with long, robust, carrot-like tail terminating in a slender, blunt point; and 35

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Austral geckos Family Diplodactylidae Austral geckos (Diplodactylidae) are an ecologically diverse and widespread group geckos found across much of mainland ­Australia, as well as New Zealand and New Caledonia. Currently, there are over 160 species of diplodactylid geckos in 25 genera recognised globally. In ­Australia, Diplodactylidae are represented by 102 species in 10 genera, of which 36 species in eight genera occur in the Northern Territory. Austral geckos occur across the Northern Territory and are a conspicuous feature of the terrestrial gecko fauna in many bioregions. Like most ­ Australian geckos (infraorder Gekkota: Carphodactylidae; Diplodactylidae; Gekkonidae; and Pygopodidae), they lack eyelids, have the ability to vocalise and lay two eggs (some Gehyra only lay a single egg). Diplodactylids typically lay softshelled eggs but, incredibly, some species originating in cooler regions of New Z ­ ealand have evolved the ability to bear live young – an extremely rare trait in geckos, which has only evolved in Diplodactylidae. Diplodactylid geckos in the Northern Territory can be broadly split into two groups based on ecology and toe pad morphology – climbing diplodactylids and terrestrial diplodactylids. All climbing diplodactylids (Amalosia, Crenadactylus, Oedura, Pseudothecadactylus and Strophurus) have complex, expanded, adhesive toe pads that allow them to agilely traverse their arboreal and saxicoline microhabitats. Among the climbing diplodactylids are some of ­Australia’s most beautiful, ornamented and impressive geckos, including the velvet geckos (Oedura spp.), spiny-tailed geckos (Strophurus spp.) and giant geckos (Pseudothecadactylus spp.). This group also includes A ­ ustralia’s smallest geckos – the clawless geckos (Crenadactylus 36

spp.)  – comparable in size to ­ Australia’s smallest skinks. Although somewhat variable in morphology, the terrestrial diplodactylids (Diplodactylus, Lucasium and Rhynchoedura) all lack the broad, flattened toes with complex, adhesive subdigital lamellae required for a predominately arboreal or saxicoline life history. Species that inhabit gravelly soils often have an expanded pair of terminal lamellae, while sandy-­ dwelling species often have reduced or minute and spinous lamellae. In the Northern Territory, most terrestrial diplodactylids share the ecological niche of exploiting ‘abandoned’ spider burrows for shelter. Some of these geckos – the fat-tailed geckos (Diplodactylus conspicillatus complex) – have taken adaptation for this niche to the extreme with evolution expertly moulding their tails into purpose-build ‘trapdoors’ to plug spider burrow entrances. Diplodactylid geckos can be distinguished from other lizards in the Northern Territory by the presence of limbs; lack of movable eyelids; non-overlapping dorsal scales; broad, fleshy tongue; flattened digits with terminal claws, if present, located in a groove; and if enlarged, elongate subdigital lamellae are present in a continuous parallel series (Pseudothecadactylus), then lamellae are also present under tip of tail. Like most geckos, diplodactylids are almost exclusively nocturnal. Most diplodactylid geckos have fairly broad, insectivorous diets; however, some of the larger species (e.g. Oedura spp.) will also eat small vertebrates, especially other geckos. Many diplodactylids have also been observed licking sap from Acacia and eucalypt trees. Some species, such as fat-tailed geckos (Diplodactylus conspicillatus complex) and beaked geckos (Rhynchoedura spp.), have very specialised diets that seem to consist almost entirely of termites.

Lizards

Key to Diplodactylidae of the Northern Territory 1. Digits without any enlarged subdigital lamellae (A)���������������������������������������������������������������������������2 Digits with one or more pairs of enlarged subdigital lamellae (B)������������������������������������������������3 2. Rostral and mental scales rounded (C); labial scales larger than adjacent granular scales (C; part) ����������������������������������������������������������������������������������������������������������������������������������������������Lucasium Rostral and mental scales protruding and beak-like (D); labial scales about equal to adjacent granular scales (D)���������������������������������������������������������������������������������������������Rhynchoedura 3. At least some digits have claws������������������������������������������������������������������������������������������������������������������4 All digits are clawless����������������������������������������������������������������������������������������������������������Crenadactylus 4. No lamellae under tip of tail; distal pair of enlarged subdigital lamellae under each digit, distinct from and discontinuous with proximal subdigital lamellae���������������������������������������������5 Lamellae under tip of tail; enlarged subdigital lamellae in a continuous parallel series (E) ��������������������������������������������������������������������������������������������������������������������Pseudothecadactylus 5. Proximal subdigital lamellae are paired (F) �������������������������������������������������������������������������������������������6 Excluding enlarged pair of apical subdigital lamellae, proximal subdigital lamellae single (G) or granular (H) �������������������������������������������������������������������������������������������������������������������������������������������7

A

E

C

B

F

D

G

H 37

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6. Dorsal scales minute, granular and noticeably smaller than ventral scales��������������Amalosia Dorsal scales relatively flat and round, and similar in size to ventral scales �����������������Oedura 7. Digits relatively long and slender, and not distinctly flattened; apical subdigital lamellae not greatly enlarged; proximal (secondary and tertiary) lamellae rarely broad; little distinction between primary, secondary and tertiary subdigital lamellae (H)������������������������ 8 Digits relatively short and wide, and distinctly flattened; apical subdigital lamellae greatly enlarged; proximal (secondary and tertiary) lamellae broad; clear distinction between primary, secondary and tertiary subdigital lamellae (G)���������������������������������������������� Strophurus 8. Relatively short, bulbous tail, tending to abruptly taper to a blunt point; both sexes lack pre-anal pores; in males, cloacal spurs (post-anal tubercles) usually in a cluster of five or more on each side (I) �����������������������������������������������������������������������������������������������������������Diplodactylus Relatively long, tapered tail, tending to end in a point; males usually have pre-anal pores (J); in males, cloacal spurs usually in a cluster of five or fewer on each side (K)��������Lucasium

I

J

Slender velvet geckos genus Amalosia Wells & Wellington, 1984 Slender velvet geckos are a group of four small, slender arboreal gecko species. Only a single described species is known to occur in the NT; however, it is very clearly an unresolved species complex requiring close examination. Amalosia can be distinguished by the following characteristics: digits with multiple pairs of enlarged subdigital lamellae; some digits with claws; no lamellae under tip of tail; proximal subdigital lamellae paired; and dorsal scales minute, granular and noticeably smaller than ventral scales. In the NT, the Amalosia rhombifer species complex can be divided into two broad groups based on habitat association. Woodland-associated Amalosia are common and 38

K

widespread across much of the Territory, north from about Alice Springs to the ­northern coast and on many coastal islands. They are typically associated with Eucalyptus woodlands and Acacia scrublands. Often observed clinging tightly to thin, spindly branches of shrubs, but are also observed on larger trees with hollows or exfoliating bark. Rock-associated Amalosia occur in a number of apparently disjunct populations in the Gulf Uplands, Arnhem Coast, Arnhem Plateau and Victoria Bonaparte bioregions. They are typically associated with sandstone escarpment, where they are most often encountered in dead shrubs near spinifex hummocks. They can also be found in rock crevices and under cap rock. Both groups are almost entirely insectivorous.

Lizards

Zigzag velvet gecko

Amalosia rhombifer (Gray, 1845) SVL 70 mm. A small to moderately sized, slender velvet gecko with minute dorsal scales; long, cylindrical tail; and no basal webbing between third and fourth Amalosia rhombifer. Calvert Hills, NT. Brendan Schembri.

Amalosia rhombifer. Litchfield National Park, NT. Chris Jolly.

Amalosia cf. rhombifer. Bradshaw, NT. Stephen Mahony.

Amalosia cf. rhombifer. Arnhem Plateau, NT. Brendan Schembri.

toes. Dorsal colouration variable but usually shades of grey to brown with distinctly paler vertebral zone. Body dorsum usually patterned with broad, dark-edged, silvery grey zigzagged vertebral stripe from the nape to tail tip. However, in rock-associated populations, the darkedging of the pale vertebral zone is often disrupted to form open, partially dark-edged, pale vertebral botches or scattered, dark dorsolateral dashes. Lateral zones are greyish with fine dark flecks and pale spots. Head similar colour pattern to body, with the pale vertebral zone often forking at the nape and proceeding over head, and dark-edging often proceeding through the eye to snout. Tail similar to body colour pattern, sometimes with yellowish wash. Ventral surface whitish. Notes: Widespread. Occurs across most of northern ­ Australia, north from south-eastern Qld in the east and Broome, WA, in the west. In the NT, mostly recorded from tropical savannas north of Newcastle Waters; however, sparse records also exist throughout the semi-arid zone centred around Tennant Creek and the Devils Marbles. There also appears to be an isolated population in Alice Springs. This species also occurs on many coastal NT islands. Both woodland and rockassociated populations exist across northern NT. Inhabits tropical savanna woodlands, sandstone escarpment and semi-arid Acacia shrublands. Taxonomic notes: Amalosia rhombifer appears to be a species complex requiring detailed genetic and morphological work to resolve. Similar species: A. obscura

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Clawless geckos genus Crenadactylus Dixon & Kluge, 1964 Clawless geckos are a group of seven extremely small (SVL less than 35  mm) species of gecko, making them ­Australia’s smallest geckos. Until recently, ­Australia only had a single recognised species of Crenadactylus, containing four subspecies. Recent taxonomic work now recognises seven species, two of which occur in the NT. Crenadactylus can be distinguished by the following characteristics: digits with multiple pairs of enlarged subdigital lamellae; and all digits are clawless. Along with their tiny size, the very secretive nature of the spinifex-dwelling

Key to Crenadactylus of the Northern Territory 1. Original tail without enlarged tubercles; usually only one (range 1–2) enlarged internasal scale (A); rostral scale in full contact with nostril (A); restricted to rocky ranges of central A ­ ustralia�����������������C. horni Original tail with enlarged tubercles; usually two or three (range 1–4) small internasal scales (B); rostral scale in narrow contact with, or occasionally excluded from, nostril (B); occurs in the rocky ranges of the Gulf of Carpentaria and the Ord and Victoria River regions of the NT��������� C. naso

Central Uplands clawless gecko

Crenadactylus horni (Lucas & Frost, 1895) SVL 35  mm. A moderately large, robust clawless gecko usually with only one (sometimes two) enlarged internasal scale; and rostral scale in full contact 40

Crenadactylus found in the NT can make them difficult to find in the wild. They spend considerable amounts of time within and beneath spinifex hummocks, even at night, resulting in limited opportunity to locate them via eyeshine. Their small size also results in duller eyeshine that is easy to overlook, particularly as it often partially obscured by overhanging vegetation. Usually encountered at the base of spinifex hummocks or moving across open rock at night, or beneath spinifex hummocks and cap rock during the day. Likely entirely insectivorous. Clawless geckos are distributed in discontinuous populations across northern and central NT.

A

B

with nostril. Dorsal body scales are homogenous, smooth or feebly keeled and no enlarged tubercles on original tail. Dorsal colouration tan, grey to dark brown with well-defined pale and dark longitudinal stripes. Doral body usually patterned with narrow, dark-edged, silvery grey vertebral stripe, mid-brown paravertebral stripes, pale laterodorsal stripes that extend above eyes to snout and broad, dark-edged, mid-brown dorsolateral stripes that extend through eyes to snout. Lateral

Lizards

Crenadactylus horni. West MacDonnell Ranges, NT. Brendan Schembri.

rostral scale in narrow contact with, or occasionally excluded from, nostril. Dorsal body scales are homogenous, smooth to weakly keeled and with enlarged pale tubercles on original tail. Dorsal colouration light grey to dark grey with weak to well-defined pale and dark longitudinal stripes. Doral body usually patterned with dark-edged, pale vertebral stripe which often forks behind head, mid-brown paravertebral stripes with dark brown borders, dark-edged, pale dorsolateral stripes that extend from snout to along tail. Dorsum often has small, scattered pale scales, sometimes bordered by dark brown scales forming small ocelli. Dark-edged, brown lateral zones with weakly defined, greyish brown lateral stripes. Head with continuation of body colour pattern. Tail with pale enlarged tubercles, occasionally with black scales adjacent. Ventral surface pale with fine, dark stippling. Notes: Occurs across northern A ­ ustralia in two disjunct

Crenadactylus horni. Musgrave Ranges, NT. Brendan Schembri.

zones are pale tan to grey with irregular dark stippling, occasionally forming one or two broken or poorly defined lateral stripes. Head and tail with continuation of body colour pattern. Ventral surface pale with moderate to weak stippling. Notes: Occurs in apparently isolated populations in the rocky ranges of central A ­ ustralia, with populations in the McDonnell Ranges (NT), Burt Plains (NT) and Central Ranges (NT–SA). Recorded as far north as Wilora and east to near the Dulcie Ranges National Park, NT. Inhabits spinifex-dominated rocky outcrops. Shelters beneath spinifex hummocks or under cap rock. Similar species: C. naso

Crenadactylus naso. Caranbirini Conservation Reserve, NT. Brendan Schembri.

Northern clawless gecko

Crenadactylus naso Storr, 1978 SVL 31  mm. A small, slender clawless gecko usually with two or three (range 1–4) small internasal scales; and

Crenadactylus naso. Limmen National Park, NT. Jordan Mulder. 41

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populations: the western population occurs in the Victoria Bonaparte bioregion, NT, with most records from Gregory (Judbarra) National Park, and throughout the Kimberley region, WA; and the eastern population occurs in the Gulf Uplands, NT–Qld. Similar geckos have also been recorded from the Kalumpurlpa area, approximately 60 km north-west of Threeways.

Inhabits spinifex-dominated rocky screes, pavements, outcrops and gorges. Also recorded from thick leaf litter in rocky vine thicket. Shelters beneath spinifex hummocks, under cap rock, and within leaf litter. Taxonomic notes: Crenadactylus naso is known to be a species complex requiring detailed morphological work to resolve. Similar species: C. horni

Stone geckos genus Diplodactylus Gray, 1882

Most Diplodactylus geckos in the NT belong to a closely related, morphologically conservative group of geckos known as the fat-tailed geckos. Until relatively recently, all fat-tailed geckos were lumped into a single, variable species  – Diplodactylus conspicillatus – but molecular work showed this to be a complex of eight species. All fat-tailed geckos possess a short, blunt, spade-shaped tail that they use to plug the entries of the spider burrows in which they shelter. While other Diplodactylus, Lucasium and Rhynchoedura species exploit spider burrows for shelter, only the fattailed geckos have evolved a morphological feature that allows them to plug the entry to exclude intruders. Interestingly, when disturbed in the open, fat-tailed geckos will also use their hard, plate-like tail defensively to protect their heads from a would-be attacker. Fat-tailed geckos can easily be distinguished from other NT Diplodactylus by their unique tail morphology, as well as their mostly granular labial scales. The remaining two Diplodactylus (D. galeatus and D. tessellatus) have more elongate, cylindrical tails and enlarged labial scales. Diplodactylus are almost entirely insectivorous. They occur throughout the NT. While some species are exceptionally common in the arid zone, they become a much less common component of the gecko fauna further north.

Diplodactylus are a group of 27 small to moderate-sized, robust, terrestrial gecko species with shortish, usually swollen tails. Seven species occur in the NT. Diplodactylus can be distinguished by the following characteristics: digits with one or more pairs of enlarged subdigital lamellae; at least some digits with claws; no lamellae under tip of tail; distal pair of enlarged subdigital lamellae under each digit, distinct from and discontinuous with, proximal subdigital lamellae; excluding enlarged pair of apical subdigital lamellae, proximal subdigital lamellae single or granular; digits relatively long and slender, and not distinctly flattened; apical subdigital lamellae not greatly enlarged; proximal (secondary and tertiary) lamellae rarely broad; little distinction between primary, secondary and tertiary subdigital lamellae; relatively short, bulbous tail, tending to abruptly taper to a blunt point; both sexes lack pre-anal pores; and, in males, cloacal spurs (post-anal tubercles) usually in a cluster of five or more on each side. They are most similar to Lucasium, from which they can typically be distinguished by their relatively short, bulbous tail shape, at most terminating in a very blunt point (Lucasium typically have long, tapered tails terminating in a point).

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Key to Diplodactylus of the Northern Territory 1. Tail short, bulbous and dorsoventrally flattened; most labials small and granular, similar in size to adjacent loreals (A) ���������������������������������������������������������������������������������������������������������������������������2 Tail relatively elongate and round in cross-section; most labials distinctly larger than adjacent loreal scales (B) ������������������������������������������������������������������������������������������������������������������������������6 2. Original tail spade-like without an attenuated tip (C)������������������������������������������������������������������������3 Original tail with attenuated tip (D) ���������������������������������������������������������������������������������������������������������5 3. Original dorsal tail scales in transverse rows of both large and small scales (C)����������������������4 Original dorsal tail scales relatively large and not arranged in clear transverse rows (E)�������� ������������������������������������������������������������������������������������������������������������������������������������������������������������������� D. hillii 4. Mid-dorsal scales on trunk small and only slightly larger than dorsolateral scales������������������ ����������������������������������������������������������������������������������������������������������������������������������������������������D. barraganae Mid-dorsal scales on trunk plate-like and appreciably larger than dorsolateral scales����������� ������������������������������������������������������������������������������������������������������������������������������������������������ D. conspicillatus

A

B

C

D

E

F

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5. Scales on nape granular and only slightly larger than granules on side of neck; original tail with short, attenuated tip (D)�����������������������������������������������������������������������������������������������������D. custos Scales on nape plate-like and appreciably larger than granules on side of neck; original tail with long, attenuated tip (F)�������������������������������������������������������������������������������������������������D. laevis 6. Dorsal body colour pattern composed of four to six large, pale, dark-edged oval or diamond-shaped blotches; ventral surface uniformly whitish����������������������������������D. galeatus Dorsal body colour pattern obscure and variable but never with large, distinct dorsal blotches; ventral surface whitish with scattered dark spots����������������������������������� D. tessellatus

Gulf fat-tailed gecko

Diplodactylus barraganae Couper, Oliver & Pepper, 2014 SVL 50 mm. A small fat-tailed gecko with a bulbous, spadelike original tail that lacks an attenuated tip; original dorsal tail scales arranged in transverse rows of both large and small scales; small and granular labials; and mid-dorsal scales on trunk small, only slightly larger than dorsolateral scales. Dorsal colouration tan to reddish brown, suffused with darker pigment of dorsum and flanks. Dorsal body usually patterned with diffuse pale spots, obscure, dark reticulations and a pale, continuous or broken vertebral zone. Head with numerous dark scales that often form a fine, netted pattern, with a moderately well-developed pale canthal stripe. Ventral surface off-white and immaculate. Notes: Occurs over a broad band

Diplodactylus barraganae. Calvert Hills, NT. Jordan Mulder. 44

of tropical woodland along the southern edge of the Gulf of Carpentaria, from Mount Isa, Qld, to the Roper River area, NT. Appears to be most common on low gravelly rises vegetated with lancewood (Acacia shirleyi) and bullwaddy (Macropteranthes kekwickii). Presumably shelters in narrow burrows excavated by invertebrates, particularly spiders. Similar species: D. conspicillatus; D. hillii

Variable fat-tailed gecko

Diplodactylus conspicillatus Lucas & Frost, 1897 SVL 63 mm. A large fat-tailed gecko with a short, bulbous, spade-like original tail that lacks an attenuated tip; original dorsal tail scales usually arranged in transverse rows of both large and small scales; small and granular labials; and mid-dorsal scales on trunk plate-like, appreciably larger than dorsolateral nape scales. Colour pattern variable. Dorsal colouration typically tan to mid-brown, heavily chequered with small dark blotches that may coalesce to form a reticulated pattern and diffuse pale spots. Paler individuals more uniform, finely peppered with darker markings and pale spots. Pale spots generally most prominent on flanks. Some specimens have a raggededged, pale vertebral stripe. Head generally with darker crown, with a prominent pale canthal stripe. Ventral surface off-white and immaculate. Notes: Occurs throughout much of central A ­ustralia, including arid and

Lizards

Diplodactylus conspicillatus. Note the lack of a long, attenuated tail tip. Victoria River region, NT. Brendan Schembri.

Diplodactylus custos. North Kimberley, WA. Brendan Schembri.

Diplodactylus conspicillatus. Simpsons Gap, NT. Chris Jolly.

semi-arid areas of southern and central NT. Scattered records exist through the wet–dry tropics to as far north as Ramingining, NT. Currently unrecorded in the Tanami and Simpson Strzelecki Dunefields bioregions, but possibly present. Inhabits a very wide range of habitats from sparely vegetated gibber plains to open woodlands, but is generally associated with harder, stony, clay and compacted sandy substrates. Shelters in narrow, vertical spider burrows. Similar species: D. barraganae; D. custos; D. hillii; D. laevis

Kimberley fat-tailed gecko

Diplodactylus custos Couper, Oliver & Pepper, 2014 SVL 58 mm. A fat-tailed gecko with a short, bulbous original tail with a short, attenuated

Diplodactylus custos. Defensive posture. Kununurra, WA. Brendan Schembri.

tip; original dorsal tail scales usually uniform in size and arranged in transverse rows; small and granular labials; mid-dorsal scales on trunk plate-like, appreciably larger than dorsolateral nape scales; and scales on nape granular and only slightly larger than granules on side of neck. Colour pattern variable. Dorsal colouration grey to reddish brown, weakly patterned with diffuse fine, darker mottling and pale spots and blotches. Vertebral zone broken by dark, obscure to well-formed transverse bars. Head finely patterned with dark pigment, with a pale canthal stripe. Ventral surface offwhite and immaculate. Notes: Occurs throughout the Kimberley region, WA, from Kununurra and Purnululu National Park to Derby and Yampi. Yet to be recorded in the NT, but the habitats associated with the Ord ­Victoria Plain bioregion from which some of

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the paratypes were collected in Kununurra are continuous from northern WA into the NT, and these records are within 50 km of the western NT border. Inhabits tropical and semi-arid woodlands and grasslands, occurs on sandy to stony soils. Shelters in narrow, vertical spider burrows. Similar species: D. conspicillatus; D. laevis

Helmeted gecko

Diplodactylus galeatus Kluge, 1963 SVL 55  mm. A small, robust gecko with a relatively elongate tail that is round in cross-­section; and most labials distinctly larger than adjacent loreal scales. Dorsal colouration pale brown to reddish brown with four to six large, pale, dark-edged oval or diamond-shaped blotches on body. Flanks with scattered pale spots. Tail with a continuation of dorsum colour pattern. Head crowned by a pale blotch, edged posteriorly by a curved dark line. Ventral surface whitish and immaculate. Notes: Occurs in two apparently disjunct populations in arid A ­ ustralia: one associated with the Stony Plains bioregion in central SA and southern central NT and the other associated with the MacDonnell Ranges bioregion in central NT. Inhabits rocky flats, screes, slopes and ranges. Shelters beneath small, surface stones during cool conditions and in deep crevices and invertebrate burrows during hot conditions.

Diplodactylus galeatus. West MacDonnell Ranges, NT. Brendan Schembri. 46

Northern fat-tailed gecko Diplodactylus hillii Longman, 1915

SVL 52 mm. A fat-tailed gecko with a short, bulbous, spadelike original tail that lacks an attenuated tip; original dorsal tail scales relatively large and not arranged in clear transverse rows; small and granular labials; and mid-dorsal scales small, only slightly larger than dorsolateral scales. Colour pattern variable. Dorsal colouration tan to midbrown, heavily marked with small dark blotches forms a broad reticulated pattern and diffuse pale spots. Pale spots generally most prominent on flanks. Some specimens have a raggededged, pale vertebral stripe. Head finely patterned with dark pigment, with a prominent pale canthal stripe. Ventral surface off-white

Diplodactylus hillii. Daly River area, NT. Brendan Schembri.

Diplodactylus hillii. Defensive posture. Delamere, NT. Chris Jolly.

Lizards

and immaculate. Notes: Endemic to the NT. Occurs throughout central and western Top End, from rural ­ Darwin inland to Elsey National Park. Inhabits tropical woodland, particularly on hard, compacted, sometimes gravelly, soils. Shelters in narrow, vertical spider burrows. Similar species: D.  ­barraganae; D. conspicillatus

Desert fat-tailed gecko

Diplodactylus laevis (Sternfield, 1924) SVL 65 mm. A large fat-tailed gecko with a bulbous original tail with a long, attenuated tip; original dorsal tail scales usually arranged in transverse rows of both large and small scales; small and granular labials; mid-dorsal scales on trunk plate-like, appreciably larger than dorsolateral nape scales; and scales on nape plate-like and appreciably larger than granules on side of neck. Colour pattern variable. Dorsal colouration tan to mid-brown with a dark reticulated pattern of fine to moderate wavy lines across entire dorsum and fine pale spots. Pale spots generally most prominent on flanks. Head with dark reticulated pattern and a pale canthal stripe. Ventral surface off-white and immaculate. Notes: Occurs across much of the ­Australian arid zone, from the Pilbara coast through much of central WA, north-western SA, south-western Qld and the southern

Diplodactylus laevis. Note the long, attenuated tail tip. Yulara, NT. Chris Jolly.

Diplodactylus laevis. Yulara, NT. Brendan Schembri.

half of NT. In the NT, it is recorded from the Tanami and Great Sandy Desert bioregions, but probably also occurs through the Simpson Strzelecki Dunefields bioregion. Inhabits various open, typically spinifex-dominated habitats. In the NT, appears to be most common on compact, sandy soils, such as dune swales and sandplain. Presumably shelters in narrow burrows excavated by invertebrates, particularly spiders. Similar species: D. barraganae; D. conspicillatus; D. custos; D. hillii

Tessellated gecko

Diplodactylus tessellatus (Günther, 1875) SVL 50  mm. A small gecko with a relatively elongate tail that is round in cross-section and ringed with enlarged conical scales; and most

Diplodactylus tessellatus. Brunette Downs, NT. Jordan Mulder. 47

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labials distinctly larger than adjacent loreal scales. Dorsal colouration grey to reddish brown with obscure, variable colour pattern of irregular darker mottling and white spots on flanks. Head and tail with a continuation of dorsum colour pattern. Ventral surface whitish with scattered dark spots. Notes: Occurs through much of interior eastern ­Australia in

association with alluvial clay soils. In the NT, occurs through the Mitchell Grass Downs of the Barkly Tablelands, the Stony Plains near Finke, and in an isolated population associated with the MacDonnell Ranges bioregion. Inhabits grasslands associated with alluvial, cracking clay. Shelters in soil cracks and invertebrate burrows.

Ground geckos genus Lucasium Wermuth, 1965

adjacent granular scales (L. damaeum). They are most similar to Diplodactylus, from which they can typically be most easily distinguished by their relatively long, tapered tails tending to terminate in a point (Diplodactylus typically have a relatively short, bulbous tail shape, at most terminating in a very blunt point). Lucasium species in the NT can be tricky to distinguish. As a genus, they are morphologically conservative; however, they often display considerable colour pattern variation within species, which sometimes overlaps with adjacent species. Although colour pattern can be a useful way to distinguish most sympatric species, differences can be locality specific and close examination of subdigital lamellae with a hand lens, or DSLR and macro lens, may be needed. Lucasium are almost entirely insectivorous, but are occasionally observed licking tree sap. They occur throughout the NT and are a common feature of the grounddwelling gecko fauna, sometimes occurring at high abundance in small areas. They inhabit a wide variety of typically well-drained, flattish habitats, in which they tend to exploit spider burrows for shelter.

Ground geckos are a group of 14 small to moderate-sized, slender terrestrial gecko species. Six species occur in the NT. ­Lucasium can be distinguished by the following characteristics: digits with (or without: L. damaeum) one or more pairs of enlarged subdigital lamellae; at least some digits with claws; no lamellae under tip of tail; distal pair of enlarged subdigital lamellae under each digit, distinct from and discontinuous with, proximal subdigital lamellae; excluding enlarged pair of apical subdigital lamellae, proximal subdigital lamellae single or granular; digits relatively long and slender, and not distinctly flattened; apical subdigital lamellae not greatly enlarged; proximal (secondary and tertiary) lamellae rarely broad; little distinction between primary, secondary and tertiary subdigital lamellae; relatively long, tapered tail, tending to end in a point; males usually have preanal pores; and, in males, cloacal spurs usually in a cluster of five or fewer on each side. If lacking enlarged subdigital lamellae, rostral and mental scales rounded, and labial scales larger than

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Lizards

Key to Lucasium of the Northern Territory 1. Digits with at least an enlarged apical pair of subdigital lamellae (A)������������������������������������������2 Digits without enlarged subdigital lamellae (B) �����������������������������������������������������������L. damaeum 2. Dorsal body scales small and homogenous without enlarged tubercles ����������������������������������3 Dorsal body scales heterogenous with scattered, enlarged, conical tubercles���������L. byrnei 3. Dorsal body colour pattern not composed of large, pale blotches; proximal subdigital lamellae are granular (C) or rounded (D)������������������������������������������������������������������������������������������������4 Dorsal body colour pattern composed of large, pale blotches; proximal subdigital lamellae are enlarged and rectangular (E)������������������������������������������������������������������������L. occultum 4. Dorsal body colour pattern variable, often with a pale vertebral stripe, and with pale spots not forming lateral bars; proximal subdigital lamellae are small and granular (C); apical subdigital lamellae are small and toe tips do not appear expanded from above���������������������������������������������������������������������������������������������������������������������������������������������������������5 Dorsal body colour pattern almost always with a pale vertebral stripe, typically with series of pale transversely aligned dots forming lateral bars; proximal subdigital lamellae are slightly enlarged (D); enlarged apical subdigital lamellae cause toe tips to appear expanded from above���������������������������������������������������������������������������������������������������� L. immaculatum

A

F

B

C

D

E

G

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5. Rostral usually in point contact with nostril (F); usually only two precloacal pores; colour pattern typically with a uniform dark reddish brown background with large pale spots in higher contrast to background�������������������������������������������������������������������������������������������L. microplax Rostral not in contact with nostril (G); usually two to five precloacal pores; colour pattern variable, but typically lighter background with smaller pale spots not distinctly contrasting with background��������������������������������������������������������������������������������������L. stenodactylus

Gibber gecko

Lucasium byrnei (Lucas & Frost, 1896) SVL 55  mm. A large-headed ground gecko with enlarged, widely spaced apical pair of subdigital lamellae on each digit. Dorsal body scales are heterogenous with scattered, enlarged, reddish or white conical tubercles. Dorsal colouration pale yellowish grey to dark reddish brown with four large, irregular pale

blotches along vertebral zone and small, irregular pale blotches on flanks. Head pale crowned with or without dark spots. Tail reddish brown with continuation of pale dorsal blotching. Ventral surface whitish and immaculate. Notes: Occurs through interior south-eastern Australia in association with the Channel ­ Country and Stony Plains bioregions through western NSW and Qld, and the eastern interior of SA. Narrowly distributed in NT where the Stony Plains breach the southern border in the Finke region of central NT. Also known from a single record from gibber plains near Ranken, NT. Inhabits shrublands on heavy soiled gibber plains. Presumably shelters deep in soil crevices or invertebrate burrows.

Beaded gecko

Lucasium damaeum (Lucas & Frost, 1896)

Lucasium byrnei. Beddome Ranges, NT. Peter McDonald.

Lucasium byrnei. Coober Pedy, SA. Chris Jolly. 50

SVL 55 mm. A slender ground gecko without enlarged, apical pair of subdigital lamellae on each digit, subdigital lamellae are granular and spinous. Dorsal body scales are small and homogenous without enlarged tubercles. Dorsal colouration pale to rich reddish brown typically with pale, straight-edged or deeply notched vertebral stripe, sometime broken into series of pale vertebral blotches or spots. Flanks reddish brown with a series of large whitish spots. Head reddish brown with scattered pale flecks and lines and, often broken, pale canthal stripes that pass over eyes and meet behind head, sometimes connecting pale vertebral stripe. Tail reddish brown with continuation of pale vertebral blotching. Ventral surface whitish, immaculate and usually

Lizards

Lucasium damaeum. Simpson Desert, NT. Jordan de Jong.

sharply demarcated from flanks. Notes: Occurs throughout semi-arid and arid areas of interior southern central A ­ ustralia through north-western Vic, western NSW, south-western Qld, interior of SA, interior south-eastern WA and southern NT. In the NT, occurs through sandy arid areas south from about the latitude of the Plenty Highway. Inhabits sandplain and dunefields vegetated with spinifex. A swift gecko often observed foraging in open areas. Shelters in narrow burrows excavated by invertebrates, particularly spiders. Similar species: L. microplax; L. stenodactylus

Pale-striped ground gecko Lucasium immaculatum (Storr, 1988)

SVL 54  mm. A moderately sized ground gecko with slightly enlarged proximal subdigital lamellae; and enlarged, apical pair of subdigital lamellae on each digit, which cause toe tips to appear expanded from above. Dorsal body scales are small and homogenous without enlarged tubercles. Dorsal colouration pale to dark reddish brown almost always with a narrow, cream to yellowish vertebral stripe, and typically with a series of pale transversely aligned dots forming lateral bars. Aberrant colour pattern of pale dorsal blotches instead of vertebral stripe has been recorded near Darwin.

Lucasium immaculatum. Hayes Creek, NT. Chris Jolly.

Lucasium immaculatum. Aberrant colour pattern. Cox Peninsula, NT. Brendan Schembri.

Flanks reddish brown with pale transverse bars and scattered whitish dots. Head reddish brown with scattered pale flecks and lines and, sometimes broken, pale canthal stripes that pass over eyes and meet behind head, often connecting to pale vertebral stripe. Tail reddish brown with continuation of dorsal pattern, with pale vertebral stripe broken into series of vertebral blotches. Ventral surface whitish, immaculate and usually sharply demarcated from flanks. Notes: Occurs through tropical, semi-arid and arid areas of central northern ­Australia through north-western Qld and eastern and northern NT. In the NT, occurs throughout the Top End, Victoria River region, Gulf of Carpentaria and Barkly Tableland regions. Inhabits grassland to woodland on heavy, often stony, soils. Often misidentified as L. stenodactylus, particularly in the Top End. Does not appear to be sympatric with L. stenodactylus, which tend to be associated with sandier soils where their ranges 51

F i e l d G u i d e t o t h e R e p t i l e s o f t h e N o r t h e r n Te r r i t o r y

overlap. Shelters in narrow burrows excavated by invertebrates, particularly spiders. Similar species: L. stenodactylus

Southern sandplain gecko Lucasium microplax Eastwood, Dougherty, Hutchinson & Pepper, 2020

SVL 56  mm. A moderately sized ground gecko with granular proximal subdigital lamellae; very small apical pair of subdigital lamellae on each digit, which does not cause toe tips to appear expanded from above; rostral usually in point contact with nostril; and usually only two precloacal pores. Dorsal body scales are small and homogenous without enlarged tubercles. Dorsal colouration dark reddish brown with welldefined, narrowly dark-edged, pale vertebral stripe. Flanks dark reddish brown highly contrasting with pale yellowish spots that may or may not be connected to vertebral stripe. Head dark reddish brown with irregular diffuse pale blotches, and pale canthal stripes that pass over eyes and meet behind head, often connecting to pale vertebral stripe. Tail dark reddish brown with continuation of dorsal pattern, with pale vertebral stripe broken into series of vertebral blotches. Ventral surface whitish, immaculate and usually sharply demarcated from flanks. Notes: Occurs throughout semi-arid and arid areas of interior southern central ­ Australia through the Central Ranges, WA, interior SA,

Lucasium microplax. Kulgera, NT. Brendan Schembri. 52

Lucasium microplax. Owen Springs, NT. Aaron Fenner.

north-western NSW, south-western Qld and central southern NT. In the NT, occurs through the arid centre north to about Barrow Creek. Inhabits shrubland on compact sandplain, sandy clay to stony soils. Does not appear to be sympatric with L.  stenodactylus, which tend to be associated with sandier soils. Presumably shelters in narrow burrows excavated by invertebrates, particularly spiders. Similar species: L. stenodactylus

Yellow-snouted ground gecko

Lucasium occultum (King, Braithwaite & Wombey, 1982) SVL 41  mm. A small ground gecko with enlarged, rectangular proximal subdigital lamellae; and enlarged, apical pair of subdigital lamellae on each digit, which cause toe tips to appear expanded from above. Dorsal body scales are small and homogenous without enlarged tubercles. Dorsal colouration reddish brown with a series of large, squarish pale blotches. Flanks reddish brown with scattered whitish or yellowish dots. Head with yellowish brown cap and reddish brown stripe from rostral, through eyes, often meeting at nape. Rostral and internasal scales yellowish. Tail reddish brown with continuation of dorsal pattern. Ventral surface whitish and immaculate. Notes: Endemic to the NT. Restricted to tropical woodlands between the Mary and South Alligator

Lizards

with nostril; and usually two to five precloacal pores. Dorsal body scales are small and homogenous without enlarged tubercles. Dorsal body colouration highly variable but typically yellowish to light reddish brown often with pale vertebral stripe, sometimes

Lucasium occultum. Point Stuart area, NT. Chris Jolly.

Lucasium stenodactylus. Barunga, NT. Jordan Mulder.

Lucasium occultum. Point Stuart area, NT. Chris Jolly.

Rivers, NT. Inhabits tropical E. tetradonta/­ miniata woodland with a dense grassy understorey on lateritic soils. Shelters in narrow burrows excavated by invertebrates, particularly spiders. Endangered (Commonwealth; IUCN Red List); Lucasium stenodactylus. Elliott, NT. Jordan Vulnerable (NT). Similar species: L. immacuMulder. latum; L. stenodactylus

Western sandplain gecko

Lucasium stenodactylus (Boulenger, 1896) SVL 57 mm. A highly variable ground gecko with granular proximal subdigital lamellae; small apical pair of subdigital lamellae on each digit, which does not cause toe tips to appear expanded from above; rostral not in contact

Lucasium stenodactylus. Watarrka National Park, NT. Chris Jolly.

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broken into a series of small irregular blotches. Flanks yellowish to light reddish brown typically with a series of pale spots surrounded by a diffuse pale halo. Head yellowish to reddish brown with irregular diffuse pale blotches often forming pale cap, and pale canthal stripes that pass over eyes and meet behind head, often connecting to pale vertebral stripe. Tail yellowish to reddish brown with continuation of dorsal pattern, with pale vertebral stripe or series of pale vertebral blotches. Ventral surface whitish, immaculate and usually sharply demarcated from flanks. Notes: Occurs through much of tropical, semi-arid and arid north-western ­ Australia

through the central deserts and ­ K imberley regions, WA and much of interior NT. In the NT, occurs through much of the arid centre, except the Simpson Strzelecki Dunefields, north to about Daly River. Predominantly inhabits spinifex-dominated sandplain, but also sometimes associated with rocky and alluvial plains and claypans. In the monsoonal tropics, inhabits woodland with sandy soils. Does not appear to be sympatric with L. immaculatum, which tends to be associated with heavier soils where their ranges overlap. Shelters in narrow burrows excavated by invertebrates, particularly spiders. Similar species: L. immaculatum; L. occultum

Velvet geckos genus Oedura Gray, 1842

species changes significantly with age. Hatchlings typically have simple, highly contrasting patterns of vivid spots or crossbands on plain, dark backgrounds. Irregular pale spots and flecks develop on dark backgrounds in subadults, with the typical colour patterns being observed by adulthood. As individuals age, however, their pattern often becomes increasingly fragmented, with crossbands sometimes breaking up into series of irregular spots. Oedura are mostly insectivorous but will also take small vertebrates, particularly other geckos. Oedura have also been observed lick sap from trees. They occur throughout much of the tropical northern half of the NT, predominantly associated with rocky ranges, but are much more restricted in semi-arid and arid regions, where they are entirely restricted to the escarpment and gorges of the MacDonnell Ranges bioregion.

Velvet geckos are a group of 19 large, dorsally depressed gecko species often with vibrant colour patterns. Until relatively recently, there were thought to be only three species of velvet gecko (Oedura gracilis, O.  gemmata and O. marmorata) in the NT. Recent taxonomic revision now recognises seven species to occur in the NT. Oedura can be distinguished by the following characteristics: digits with one or more pairs of enlarged subdigital lamellae; at least some digits with claws; no lamellae under tip of tail; distal pair of enlarged subdigital lamellae under each digit, distinct from and discontinuous with enlarged proximal subdigital lamellae; proximal subdigital lamellae paired; and dorsal scales relatively flat and round, and similar in size to ventral scales. Although colour pattern is often a useful characteristic to distinguish species in this genus, the colour pattern of all

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Lizards

Key to Oedura of the Northern Territory 1. Original tail relatively short (usually 65% of SVL)����������������������������������������������������������������������������������������������5 2. Original tail relatively narrow, slightly depressed, gradually tapering to a point (A) �������������3 Original tail usually broad, dorsoventrally depressed or bulbous, with sharply tapered tip (B)���������������������������������������������������������������������������������������������������������������������������������������������������������������������������4 3. Dorsal crossbands yellow; occurs on the mainland ��������������������������������������������������������������O. bella Dorsal crossbands white; appears to be restricted to Groote Eylandt ������������������������� O. nesos 4. Dorsal body colour pattern with some crossbanding��������������������������������������������� O. marmorata Dorsal body colour pattern composed of small pale spots without crossbanding������������������ �������������������������������������������������������������������������������������������������������������������������������������������������������� O. gemmata 5. Enlarged apical subdigital lamellae under fourth toe followed by three or more pairs of enlarged, divided lamellae (C) �������������������������������������������������������������������������������������������������������������������6 Enlarged apical subdigital lamellae under fourth toe followed by two pairs of enlarged, divided lamellae (D)������������������������������������������������������������������������������������������������� O. gracilis 6. Rostral crease fully divides rostral scale (E) ����������������������������������������������������������������������������O. cincta Rostral crease divides less than 50% of rostral scale (F)������������������������������������������������������O. luritja

A

B

D

E

C

F

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F i e l d G u i d e t o t h e R e p t i l e s o f t h e N o r t h e r n Te r r i t o r y

Gulf marbled velvet gecko Oedura bella Oliver & Doughty, 2016

SVL 92  mm. A moderately sized velvet gecko with a relatively short (65% of SVL), cylindrical tail; enlarged apical subdigital lamellae under fourth toe followed by three or more pairs of enlarged, divided lamellae; and rostral crease fully divides rostral scale. Some regional variation in colour pattern. In the NT, dorsal colouration dark purplish brown usually patterned with five broad, dark-edged white crossbands between nape and hips. In hatchlings, white crossbands solid and sharp-edged, but pattern disrupts and fragments with age. With age, dark interspaces between dorsal crossbands increasingly patterned with numerous, coalescing, irregular

Oedura cincta. Simpsons Gap, NT. Chris Jolly.

Lizards

Oedura cincta. Juvenile. Trephina Gorge, NT. Brendan Schembri.

yellow spots and broad, white crossbands develop ragged grey centres. Head purplish brown patterned with numerous white and yellow spots, yellow supraocular scales, and dark continuous band from nostrils, through eyes and across nape. Labials pale. Original tail with five to eight broad, dark-edged white crossbands, and regenerated tails dark with irregular yellow and white spots and broken bands. Notes: Occurs in several isolated populations across inland south-eastern A ­ ustralia, including the Cooper Darling Basins of Qld and NSW, and the Flinders Ranges and northern Murray River region, SA. In the NT, it is restricted to a few apparently isolated populations in the northern MacDonnell Ranges, and Mount Doreen and Barrow Creek areas. NT populations inhabit rock outcrops and gorges where they shelter in rock crevices. Similar species: O. luritja

Dotted velvet gecko

Oedura gemmata King & Gow, 1983 SVL 103 mm. A large, spotted velvet gecko with a relatively short (65% of SVL), narrow tail; and enlarged apical subdigital lamellae under fourth toe followed by two pairs of enlarged, divided lamellae. Dorsal colouration dark purplish brown to blackish patterned with five or six broad, yellow crossbands between nape and hips, composed of a pair of narrow yellow bands with a dark centre. Dark interspaces between paired yellow crossbands are patterned with irregular yellow botches, sometimes forming a ragged-edged single yellow crossband. Eastern populations of this species are strikingly patterned throughout their life. Head blackish patterned with yellow canthal stripe than goes from semi-continuously from nostril to behind eye, yellow supraocular scales, and dark continuous band from nostrils, through eyes and across nape. Labials pale. Original tail with numerous paired yellow to white crossbands, and regenerated tails dark with irregular yellow and white spots and broken bands. Notes: Occurs throughout the rocky ranges of the Kimberley region, WA, and the Victoria Bonaparte bioregion, NT. In the NT, O. gracilis has only been recorded in the sandstone escarpments associated with Bullo River Station. Inhabits sandstone and granite outcrops associated with a variety of tropical and semi-arid habitats. Shelters in tight rock crevices and beneath cap rock.

Oedura gracilis. Bullo River Station, NT. Stephen Zozaya. 58

Mereenie velvet gecko

Oedura luritja Oliver & McDonald, 2016 SVL 99 mm. A relatively large velvet gecko with a long (>65% of SVL), cylindrical tail; enlarged apical subdigital lamellae under fourth toe followed by three or more pairs of enlarged, divided lamellae; and rostral crease divides less than 50% of rostral scale. Dorsal colouration dark purplish brown usually patterned with five or six relatively straight, pale buff crossbands between nape and hips. In hatchlings, buff crossbands solid and sharp-edged, but pattern disrupts and fragments with age. Increasingly with age, dark interspaces between dorsal crossbands become patterned with numerous, coalescing, irregular buff spots and broad, buff crossbands develop ragged edges,

Oedura luritja. Watarrka National Park, NT. Jordan Mulder.

Oedura luritja. Juvenile. Watarrka National Park, NT. Brendan Schembri.

Lizards

sometimes becoming obscure. Head purplish brown patterned with numerous diffuse buff spots not forming continuous stripes or lines, and bright yellow supraocular scales. Labials pale to yellowish. Original tail with seven or eight broad, ragged-edged buff crossbands, and regenerated tails dark with irregular buff mottling. Notes: Endemic to the NT. Appears to be restricted to the ranges of the southern ­MacDonnell Ranges bioregion, from Rainbow Valley Conservation Reserve in the east to Watarrka National Park in the west. Inhabits sandstone rubbly slopes, rocky pillars, outcrops and gorges. Shelters in deep, tight crevices of exfoliating sandstone, typically near vertical faces. Similar species: O. cincta

Oedura marmorata. Pine Creek, NT. Chris Jolly.

Marbled velvet gecko Oedura marmorata Gray, 1842

SVL 97 mm. A relatively large, typically banded velvet gecko with a relatively short (