On the Land (Life on Earth) 9780816050475, 0816050473

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LIFE ON EARTH

ON THE LAND

THE DIAGRAM GROUP

Life On Earth: On the Land Copyright © 2004 by The Diagram Group Written, edited, and produced by Diagram Visual Information Ltd Editorial director:

Denis Kennedy

Editors:

Bender Richardson White, Gordon Lee

Contributor:

John Stidworthy

Indexer:

Martin Hargreaves

Art director:

Roger Kohn

Senior designer:

Lee Lawrence

Designers:

Anthony Atherton, Christian Owens

Illustrators:

Julian Baker, Pavel Kostal, Kathleen McDougall, Coral Mula, Graham Rosewarne

Picture researcher:

Neil McKenna

All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Facts On File, Inc. 132 West 31st Street New York NY 10001 For Library of Congress Cataloging-in-Publication Data, please contact Facts On File, Inc. ISBN 0-8160-5047-3 Facts On File books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions, or sales promotions. Please call our Special Sales Department in New York at 212/967-8800 or 800/322-8755. You can find Facts On File on the World Wide Web at: http://www.factsonfile.com Printed in the United States of America EB Diagram

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This book is printed on acid-free paper.

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Contents 4 Introduction THE LAND 6 Land 8 Climatic zones 10 Life on land 12 Mass extinctions FOSSILS 14 Becoming a fossil 16 Dating fossils 18 Fossil fuels ANIMALS WITHOUT BACKBONES 20 Snails and worms 22 Spiders and scorpions 24 Millipedes and centipedes 26 Invertebrates AMPHIBIANS AND REPTILES 28 Frogs and toads 30 Salamanders 32 Early reptiles 34 Rise of the dinosaurs 36 Dinosaurs in variety 38 Tortoises and tuataras 40 Lizards 42 Snakes MAMMALS 44 First mammals 46 Egg-laying mammals 48 Ancient marsupials 50 Carnivorous marsupials 52 Plant-eating marsupials 54 Primitive placentals 56 Insectivores

58 60 62 64 66 68 70 72 74 76 78 80 82 84

Edentates Primates Rabbits and rodents Squirrels Mice and guinea pigs Carnivores Ancient carnivores Modern carnivores Primitive hoofed mammals South American hoofed mammals Odd-toed hoofed mammals Even-toed hoofed mammals Ruminants Elephants

BIRDS 86 Running birds BIOMES 88 Tropical rainforest 90 Temperate woodland 92 Boreal forest 94 Tropical grassland 96 Temperate grassland 98 Desert 100 Mountains 102 The polar regions 104 Timeline 106 Glossary 109 Websites to visit 111 Index

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Introduction

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his book is a concise, illustrated guide to living things that evolved on, and now inhabit, the land. Texts, explanatory diagrams, illustrations, captions, and feature boxes combine to help readers grasp important information. A glossary clarifies the more difficult scientific terms for younger students, while a list of websites provides links to other relevant sources of additional information. Chapter 1, The Land, looks at the living conditions that animals face on land, and briefly reviews the course of evolution among land animals. It also covers the topic of mass extinctions throughout the Earth’s history. Chapter 2, Fossils, tells how fossils are formed, how they are dated, and how some are important to us as fuels. Chapter 3, Animals without Backbones, gives an outline of the main groups of invertebrates, both living and extinct, that have taken to life on land. These include snails, worms, and various groups of arthropods—animals with jointed legs. Chapter 4, Amphibians and Reptiles, looks at the evolution of these two groups of vertebrates, with examples of their modern species. Chapter 5, Mammals, is the longest section, examining the ancient history of mammals, and then taking a closer look at the various main groups, or orders, that make up this important group of land animals. Chapter 6, Birds, describes those birds that have forsaken flying, to parallel the lifestyle of the running mammals. Chapter 7, Biomes, looks at the various main habitats on Earth, and how living things are adapted to them, with examples of characteristic species. On the Land is one of six titles in the Life On Earth series that looks at the evolution and diversity of our planet, its features, and living things, both past and present. The series features all life-forms, from bacteria and algae to trees and mammals. It also highlights the infinite variety of adaptations and strategies for survival among living things, and describes different habitats, how they evolved, and the

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communities of creatures that inhabit them. Individual chapters discuss the characteristics of specific taxonomic groups of living things, or types of landscape, or planetary features. Life On Earth has been written by natural history experts, and is generously illustrated with line drawings, labeled diagrams, and maps. The series provides students with a solid, necessary foundation for their future studies in science.

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Land

Biomes These are areas of similar climatic conditions where comparable types of vegetation occur.

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HE MAIN CONTINENTAL BLOCKS have not always been arranged as they are today. Over millions of years, slow geological processes have gradually shifted the “plates” of the Earth’s crust that carry the continents. At various times in the past they came together in different ways. For example, Australia, Antarctica, and South America were once connected. The geography of the past had great influence on the evolution of various animal and plant groups, and governed their ability to spread. Continental movements led to collisions that sometimes crumpled the edges of the main continental blocks slowly over millions of years. The Himalayas are the result of India moving up from the south, and colliding with the main block of Asia. The Andes have been thrust up where the Pacific Ocean plate meets South America. The Himalayas and Andes are “young” mountains, and contain many of the world’s

Land makes up about 30 percent of the Earth’s surface. It is a vast area of 57.5 million square miles (149 million sq km). Two-thirds of the land area in the present world is in the Northern Hemisphere, with Australia, most of South America, part of Africa, and some outlying islands of Asia in the Southern Hemisphere.

Biomes 1

2

4

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ON THE LAND THE LAND

highest peaks. Older mountains, such as those in Scotland, have been worn down over hundreds of millions of years, and are relatively low. The average height of the continents above sea level is about 2,756 feet (840 m), but there is a huge variation in height from the tallest mountain, Everest, at 29, 140 feet (8,882 m), to some parts of the land, such as the shore of the Dead Sea, that are as much as 1,299 feet (396 m) below sea level. The land contains some areas, such as parts of Australia, or Eastern Europe, with flat plains stretching far and wide. The enormous variation in landforms entails a similar variation in the adaptations of the animals that live there. This is one reason for the existence of a huge range of animals in the modern world, and throughout the many millions of years that animals have lived on the land. 1 3

Tropical forest biome Found near the equator where conditions are warm and very wet.

!

IT’S A FACT The world’s continents, in order of size (1,000 millions), are as follows: Continents a Asia b Africa c North America d South America e Antarctica f Europe g Australia

Sq mi 17.5 12 9.5 7 5.2 4 3.0

The world’s continents a

b

c

d

2 Desert biome Very dry, often hot, and with few plants. Covers one fifth of the land. 3 Coniferous forest biome Forests with long winters and short summers.

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4 Grassland biome Warm or temperate, but with not enough water f0r trees to grow. 5 Temperate forest biome Temperate, with enough water for tree growth. Many trees drop their leaves in winter. 6 Tundra biome Frozen for much of the year with dwarf plants.

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e f

g

Sq km 44 31 24 18 13 10 8

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Climatic zones

The world has a series of marked climatic zones. Equatorial regions are warmed by sunlight throughout the year. Temperatures are lower toward the Poles, where sunlight has to penetrate a thicker layer of atmosphere before reaching the surface.

B

ECAUSE OF THE TILT of the rotating Earth, the North and South Poles are plunged into darkness in the middle of their winters. The circulation of winds and ocean currents also affects climate, but the basic pattern is clear. The tropics are very warm throughout the year. At higher latitudes there is a temperate zone, with warm summers but cooler winters. At the highest latitudes, near the Poles, there is a cold climate all year with, at most, a brief summer during which some ice may melt. It is not surprising that, in general, life is more abundant and varied in the warm parts of the world,

January

Temperature belts in January and July Seasonal temperatures differ more the greater the distance from the equator. (Temperatures are given below in both Fahrenheit and Celsius.)

July

Below -30 F

-34 c

-30 F to 30 F

-34 c to 1 c

30 F to 50 F

-1 c to 10 c

50 F to 70 F

10 c to 21 c

70 F to 90 F

21 c to 32 c

Over 90 F

Over 32 c

0

0

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ON THE LAND THE LAND

Cretaceous period At the end of this period continents had not reached their present positions.

as long as there is water available. The icy wastes of Antarctica are least likely to support life, but there are no places on the Earth entirely devoid of living things. In mountains, temperature drops with height, so different climatic zones are found at different heights. On the highest mountains the summits tend to have an Arctic feel. The world can be divided into a number of “biomes,” defined by climate and rainfall. Each has its own typical vegetation and animal life, although the species may not be the same on different continents. But it was not always warm in the past. There is evidence of great ice ages 445 million years ago, and again about 300 million years ago. It is only recently, geologically speaking, that the world emerged from an ice age. Ice cover disappeared from North America about 11,000 years ago. Some people believe that we are now in a short, warm period within this ice age.

 !

IT’S A FACT It cannot be assumed that today’s climates are typical of the past. For much of the Cretaceous period (144 to 65 million years ago) the Earth had a warm climate. Even near the Poles it was warm, so that temperatures were far more even across the world than now. This was the heyday of the dinosaurs and pterosaurs, and they lived from the equator to the Antarctic, even though the polar winters must have been dark.

© DIAGRAM

Age of dinosaurs At his time the world enjoyed a warm climate.

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Life on land

First colonists of the land Our early mammal ancestors lived in the shadow of the dinosaurs.

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LITTLE BEFORE 400 million years ago plants began to grow on land. Their ancestors were probably green algae, but some of these new land plants developed water-conducting tissue and, soon after, supporting tissue. They could then grow upward, rather than just form a crust or flat carpet. Arthropods, the jointed-legged animals with hard outer skeletons, were the first land animals. This is not surprising, as their skin/skeleton could support them out of water, and may also have provided some protection against water loss. Their breathing apparatus could be adapted to breathing air. Some of these early land arthropods, such as scorpions, were surprisingly similar to types still living today. Few of the new land animals were adapted for eating plants directly, although some could feed on decaying vegetable matter. Most seem to have been predators. Millions of years after these first colonists of the land, some fishes took their first steps as tetrapods, four-legged “amphibians.” It was many more millions of years before the amphibians familiar to us today (frogs and salamanders) evolved. Before these arrived on the scene, some tetrapods became able to breed on dry land. By 300 million years ago these so-called amniotes gave rise to others—reptiles and the synapsid forerunners of mammals. Mammals originated from synapsids at the time of the dinosaurs. The earliest mammals did not belong to groups you could see today. The main groups of mammal we recognize now—the egglaying monotremes, the marsupials, and placental mammals like us—did not appear until much later.

Although living things had been numerous and diverse in the waters of the world for hundreds of millions of years, there is little evidence of life on land before about 400 million years ago. With its bare, weather-beaten surface, the land must originally have been a challenging place to live.

ON THE LAND THE LAND

Period

65–present Tertiary and Quaternary 144–65

Who lived at that time?

Primate

Pantodont

Cretaceous Mosasaur

206–144

Jurassic

Saurischian Omithischian

Triassic Crocodilian

290–248

Therapsid

Permian Pelycosaur

Arthropod

354–290

Arthropod

Arthropod

Labyrinthodont

Silurian Palaeophonus

490–443

Gymnosperm

Devonian Fern ancestor

443–417

Conifer

Carboniferous Protothyridid

417–354

Flowering plant

Saurischian

Bennettitalean

248–206

Perissodactyl

Rhyniophyte

Ordovician Euthycarcinoid

543–490

Cambrian

2,500–543

Proterozoic periods

Liverwort

No life on the land No life on the land

© DIAGRAM

Millions of years ago

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Mass extinctions

Uintatherium (left) A large mammal, it evolved after the extinction of the dinosaurs. Scutosaurus (right) A plant-eating reptile, it lived before the great extinction 250 million years ago.

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ON-BIRD DINOSAURS disappeared completely 65 million years ago. Not only dinosaurs, but also other reptiles, such as plesiosaurs in the sea and pterosaurs in the air, vanished. Many fishes became extinct, along with many invertebrates. Scarcely any land animals bigger than wolf-size survived. The disappearance of so many kinds of animals at the same time is known as a mass extinction. Why did so many animals disappear? We do not know for sure, but there have been many theories. It appears that a large asteroid hit the Earth at about this time, at what is now the coast of Mexico. It would have thrown up vast clouds of dust, and produced heat and fires. The Earth’s climate was probably disrupted, possibly for many years. On the other side of the world, in India, at about the same time, there was a huge outpouring of lava that covered many thousands of square miles (sq km), also affecting the climate. Even before these events though, dinosaurs were declining. Numbers had been dropping for 20 million years or so. Some shellfish also disappeared millions of years before the layer of rock that marks the “mass extinction.” Climates had been changing as sea levels dropped, making continental interiors

For about 150 million years, the dinosaurs were the dominant large animals on land. Diverse, adapted for many ways of life, and advanced for their time, they seemed destined to rule the Earth forever.

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Mass extinctions Million years ago

What was affected?

Possible cause?

445

Enormous cut in diversity of sea life

A great ice age, plus volcanic activity

355

Trilobites; many kinds of fish; sponges

Global cooling; shallow water areas much reduced

250

9o percent of species lost, including the last trilobites

Great volcanic activity; smaller seas; more extreme land climate

205

65 percent of marine species lost; over 30 percent of land vertebrates; most land plants

Rising temperatures; asteroid strikes

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All non-bird dinosaurs; other large reptiles; many other species

Climate change; asteroid strikes; volcanic activity

drier and harsher, and creating land that animals could cross between formerly separate areas, increasing competition. Perhaps the meteorite strike was a sudden event that provided the final blow to the declining groups of animals. The mass extinction that saw the end of the dinosaurs was not the only one in the Earth’s history, nor was it the most catastrophic in terms of the percentage of animals wiped out. From the rocks laid down hundreds of millions of years ago come tantalizing clues about factors that may have caused the extinctions, but from this distance in time we will probably never be sure.

Tyrannosaurus This was one of the last creatures to walk the Earth before non-bird dinosaurs disappeared 65 million years ago.

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ON THE LAND THE LAND

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Becoming a fossil

Amber (above) Millions of years ago, this fly was trapped in resin and thus preserved.

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CCASIONALLY, conditions are just right for the remains of animals and plants to be preserved in rocks. Even then, they may be destroyed by geological processes, such as erosion, on the surface. But some fossils remain preserved in rocks for millions, or even hundreds of millions, of years, and may be dug up to give us an insight into life long ago. Small, soft-bodied animals stand least chance of preservation. Animals in water may die, fall to the bottom, and be buried in mud. Their skeletons or shells may not decay. Covered eventually by a great thickness of sediment, new minerals may gradually replace bone or shell, making a hard replica of the original. Sometimes the original hard parts are instead dissolved away by acids seeping through the sediment, leaving just a hole, but one that retains the shape of the animal that was formerly there. On land, becoming a fossil is even rarer than in water. Many land animal fossils are preserved because they died in, or near, water and have been carried into mud and preserved. On land, most animals are consumed, or decay rapidly. This is particularly true of forest animals. Sometimes burial by wind-blown sand or dust, or covering by volcanic ash,

The great majority of animals and plants that die do not become fossils. They are eaten by other organisms, or decay away completely.

Fossilization Burial under water is the commonest way of becoming a fossil. An animal dies and sinks to the bottom.

The animal is buried in the mud.

Layers of mud cover the animal.

Layers of mud are crushed into hard rock.

The rock wears away and the fossil is exposed.

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ON THE LAND FOSSILS

can lead to fossilization. Small animals can be trapped in tree resin. The resin itself becomes fossilized as amber, with insects or spiders trapped within it. Relatively recent animals, from thousands rather than millions of years ago, may also be preserved by mummification in a dry climate, or by freezing in a cold one.

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STRANGE BUT TRUE It is not just animals’ bodies that become fossils. Burrows can also be preserved in rocks. Some A dinosaur’s footprint of the earliest land fossils are burrows. It is not always easy to guess what made them. Footprints and trackways can also be preserved in mud. If they can be matched to a particular animal, we can learn how, and sometimes how fast, an animal moved millions of years ago. Fossil droppings, called coprolites, are also found. Again, if their maker can be identified, it may provide information about eating habits. Even eggs and nests can be buried in the sand to become fossils.

A fossil dropping

© DIAGRAM

Fossilized tetrapods in New Mexico These “amphibians” died 200 million years ago, and were preserved in the mud of a drying-up pond.

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Dating fossils

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OMETIMES, areas of rock are deformed or folded upside-down over a certain area, but, as long as geologists recognize Archaeopteryx what has happened, This fossil comes older and younger layers from the Jurassic can be traced with precision. period (150 million From studies over large areas of the years ago). world, a picture of the sequence of rocks through the ages was built up. The major geological periods, such as the Cretaceous, were recognized by the rock formations laid down in them. It was possible to make estimates of the time it took for the huge thicknesses of Brown limestone sediments to be laid down, and so calculate the probable dates and duration of these periods. Fossil oyster bed Widespread animal species that existed for a limited time aid the recognition of sediments of the same period, even if far Brown limestone apart. Detailed detective work allowed scientists to put most rocks they found in sequence. But until the properties of Hard sandstone radioactive elements were discovered, there was no way of putting a date on a rock with any degree of certainty. Using radioactive isotopes, absolute dating is possible, at least for Green shale igneous rocks (those formed by volcanic activity). Minerals in these rocks may contain a radioactive element such as uranium-235. Atoms of this element “decay,” losing part of their nucleus, and turn into lead-207 at a steady rate. Half of a sample of this uranium will turn into lead Dark shale in 713 million years. If you measure the relative amounts of uranium-235 and lead-207 in the rock, you can establish an absolute measure of how Green shale

The simplest way of establishing when a fossil lived is to examine the layer of rock in which it was found. Layers of sedimentary rock lie on top of one another. In undisturbed rocks, upper layers are younger than lower ones.

Paleocene sandstone and tertiary basalt in Greenland caption to come

Fallen rocks

Dating fossils Layers in sedimentary rocks allow us to tell the relative dates of fossils. Lower layers are older than upper ones.

ON THE LAND FOSSILS

Geological timescale (dates given in millions of years) Eras CENOZOIC 65–Present

Periods Quaternary 1.8–Present Neogene

or Late Tertiary 23.8–1.8

MESOZOIC 248–65

Paleogene

or Early Tertiary 65–23.8

Different aged strata (left) By virtue of the relative position of strata, the comparison of fossils, and radiometric dating, the ages of strata, and their position in the geological timescale, have been established.

Epochs Holocene (Recent) 0.01–Present Pleistocene 1.8–0.01 Pliocene 5.3–1.8

much time has elapsed since the rock was originally formed. However, measurement and calculation is rarely as easy as this suggests. Different radioactive elements have different “half-lives” of decay, and are useful for different periods of the Earth’s history. Where igneous rocks occur between layers of sediment, they can give a date to the sediment. Nowadays, the ages of enough rocks have been calculated for us to have a clear idea of the likely date of most fossils, although there may still be room for some adjustments.

Miocene 23.8–5.3 Oligocene 34–23.8

Cretaceous 144–65

Eocene 55–34 Paleocene 65–55

PALEOZOIC 543–248

Jurassic 206–144 Triassic 248–206

Permian 290–248

Carboniferous 354–290

Devonian 417–354 Silurian 443–417

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Radiometric dating

By radiation potassium-40 loses half its mass every 1,310 million years (one half-life). Thus a sample‘s potassium-40 content can indicate its age, A Original sample

1/1

A

B After 1.3 billion years (one half-life) half remains. C After 2.6 billion years (two half-lives) one quarter remains. D After 3.9 billion years (three half-lives) oneeighth remains.

Ordovician 490–443

B

E After 5.2 billion years (four half-lives) onesixteenth remains.

1/2

Cambrian 543–490

C

1/4

D

1/8 1/16 0

1

2

3

4

E 5

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Fossil fuels

Coal, and underground oil and gas deposits, are all fossil fuels. They formed long ago from the remains of dead organisms. These remains were concentrated into a form which is useful to people.

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ONDITIONS HAVE NOT always been suitable for the formation of fossil fuels. Most of the deposits come from just a few of the many geological periods. No deposits of significance are being laid down now. Even though there are vast quantities in the ground, they are being used. A time will come when it is no longer possible to power civilization from fossil fuels. Much of the best coal was formed over 300 million years ago. A geological period, known as the Carboniferous (354–290 million years ago), was named because of the abundance of carbon—coal— in its rocks. During this period, plenty of swamp forests grew on low ground, with trees up to 100 feet (30 m) tall. They were club mosses and horsetails. Their present-day relatives are much smaller. When they died, they fell into acidic water and were partly preserved, instead of decaying away.

Legacy The swampy forests of 300 million years ago are the source of much of the good quality coal in use today.

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ON THE LAND FOSSILS

From time to time, seawater flooded some of the lowlying forests, and sediment was dumped on top of the plant remains, compressing them. Then the water level dropped again, plants grew, and the cycle repeated itself. Most of the time there was forest, with briefer periods when sediment was dumped. Even so, the coal seams are thin compared to the sediments surrounding them. Oil is also formed from the remains of living things. Often these were tiny sea organisms that died and accumulated at the bottom of still water. The carbon compounds in their bodies seeped down and were trapped in the rock. Deposits of natural gas are often found above oil reserves, derived from the same creatures. Particular limestone formations are associated with oil, as are some salt deposits. More than half of the world’s oil—in the rich deposits of the Middle East and the Gulf of Mexico— started forming during the second half of the time of the dinosaurs. Texan oil comes from more than 100 million years earlier.

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STRANGE BUT TRUE It is estimated that a thickness of about 100 feet (30 m) of plant remains must be compressed to provide a 3 foot (1 m) seam of coal. It would have taken 5,000 years, or even more, to produce these plants.

© DIAGRAM

Where they are This map shows some of the main areas in the world where fossil fuels are found.

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Snails and worms

Worms are some of the oldest animal types but, as they are soft-bodied, they rarely fossilize.

Body plan (below) Earthworms have a simple, segmented body plan, but are still successful soil animals.

Body wall

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OMETIMES TRACES OF THE soft bodies of worms, or fossils of hard jaw parts or burrows, are found. But nearly all are remains of marine worms. Land worms are even less likely to become fossils. Gastropod mollusks (snails) are known from over 500 million years ago, but these first snails were sea creatures. Far from fading out, snails have been increasingly successful over the last 100 million years or so. Shells fossilize well, but most gastropod fossils are from either sea or fresh water. A few are land snails related to those found in our gardens. Earthworms are the most familiar worms on land. They burrow in soils all over the world. They have bodies divided into rings called segments, sometimes as many as 200 or more. Many segments are similar, but the front segments contain the mouth and small “brain,” hearts, and reproductive organs. Most worms eat Mouth pieces of dead plants in the soil, or rotting leaves brought from the surface. Their

Segments

Anus

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DID YOU KNOW? Most earthworms are 12 inches (30 cm) long or less, but in western North America there are bigger species. In South Africa and Australia there are worms that grow to over 10 feet (3 m) in length!

ON THE LAND ANIMALS WITHOUT BACKBONES

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activities in burrowing and churning the soil help to enrich and aerate it. Worms are also an important food for Roundworm (above) This type of worm often many other kinds of animal. lives inside plants or the Even more common than earthworms, but far less visible, bodies of other animals, are roundworms. These have a totally different body plan, including humans. without segments, and with smooth tough skins. They are pointed at both ends, and the outside of the body is almost featureless. Although some are large, most are tiny or even microscopic. Some live freely in the soil, but many live as parasites inside the Digestive bodies of other animals and plants. Intestine gland (liver) Roundworms are largely hidden. Lung Snails are also unsegmented. A snail Kidney moves on a large muscular “foot.” Glands Salivary gland produce slime to smooth its way. The digestive system and other organs are Heart tucked inside a hard, coiled shell. The snail retreats into this for protection from enemies. The head bears sense Mouth Anus Ureter Stomach organs. In the mouth is a tongue covered Snails with many horny teeth that the snail Like most mollusks, snails uses to rasp at plants as it feeds.

© DIAGRAM

have a complex internal structure (above), and shells made of calcium carbonate (below).

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Spiders and scorpions

Eotarbus (above) This was one of the first creatures to inhabit the land about 415 million years ago. Bird spider (below) This bird-eating spider measures about two and a half inches (6 cm) in length, and comes from Panama.

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HE FIRST FOSSILS of actual animals date from as much as 415 million years ago, and include a scorpion and a tiny arachnid named Eotarbus. This was not in fact a spider, but it did resemble present-day spiders and mites. Around 395 million years ago, a place called Rhynie in Scotland was full of volcanic springs, around which grew miniature forests of primitive plants. They, and the animals living in them (including mites and relatives of Eotarbus), became fossilized. In some, so-called book lungs are preserved; these are folded structures that are found in living scorpions (and some spiders). They are used for breathing air, and were probably modified from gills of aquatic ancestors. The earliest known “true” spider was found in rocks from the eastern United States about 375 million years ago. It had fangs with poison glands, and also a spinneret—an organ that feeds out the silk of the web. It looks as though, even then, spiders were spinning webs or trap lines. Spiders, scorpions, and mites are all arachnids. These animals have segmented bodies (though the segmentation is not obvious in many spiders) and eight walking legs. In front of these, other pairs of legs are turned into jaws. In scorpions they include a pair of large pincers for seizing prey. In

Tracks and burrows suggest that there may have been animals on land as long as 450 million years ago.

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ON THE LAND ANIMALS WITHOUT BACKBONES

Scorpion (left) While seizing prey with their pincers, scorpions may also use the sting in their tail to subdue it.

spiders there are downward-stabbing fangs in the more primitive types, or pincerlike fangs in the more advanced. All spiders produce venom from their fangs, but although lethal for small prey, few kinds are dangerous to humans. Scorpions have a venom gland attached to the sting at the tip of the tail. Again, the venom kills small animals, but few scorpions are a threat to us. Both spiders and scorpions have a long history, but nowadays there are only about 1,200 kinds of living scorpion. More than 35,000 kinds of spider have been named. There are other types of arachnid including “false scorpions,” sun spiders, and at least 30,000 kinds of mite. There are probably many more tiny mites in existence, many living on, or else inside, other living organisms, but we have a tendency to notice mainly those that cause discernible diseases in both domestic animals and plants.

Dust mite (right) Although this creature is microscopic in size, some people are allergic to it.

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False scorpion These are tiny arachnids that are found in leaf litter.

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Millipedes and centipedes

For posterity (above) An ancient millipede is trapped in amber.

Arthropleura (above) This millipede lived 300 million years ago, and was 6 feet (2 m) long.

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N LAND, fossil burrows from 450 million years ago have been interpreted as belonging to millipedes, and pellets of plant remains from 410 million years ago could be millipede droppings. Remains of centipedes from over 400 million years ago, and millipedes from at least 375 million years ago, confirm them as among the earliest-known land animals. Giant relatives of millipedes 6 feet (1.8 m) long and 20 inches (50 cm) wide trundled across the land 315 million years ago, leaving marks resembling railway tracks. Both centipedes and millipedes have a head with specialized segments carrying jaws and sense organs, but behind the head the segments are mostly very similar to one another, and bear pairs of walking legs. These animals hatch from an egg with only a small number of segments, and add more until they reach adulthood. With a few exceptions, the 10,000 or so species of millipede are plant eaters, feeding on dead or dying vegetation. They tend to tunnel into the earth, or else push through the leaf litter. Even after millions of years of evolution, they have not developed a waterproof coat to the skin, and are usually found in damp places. Most millipedes have simple

Centipedes and millipedes are ancient animal types, whose relatives lived in the sea 500 million years ago.

Millipede head (below) Jaws that have adapted for nibbling plants remain.

Millipede head

Eye

Antenna Walking legs

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ON THE LAND ANIMALS WITHOUT BACKBONES

Centipede

mouthparts adapted for chewing bits of plant, although some tropical species can suck plant juices. Their eyes are simple, and it is doubtful if they can form images. Feelers are used to touch and scent the surroundings. Many millipedes can repel attackers with foul-tasting or poisonous fluids from glands along the side of the body. Although most millipedes are inconspicuous, some tropical species grow to 10 inches (25 cm) or more. Centipedes are carnivores, and feed on insects and other small animals. They have jaws with poison fangs. Some of the largest tropical species, 13 inches (33 cm) long, can give a nasty bite to a human, or kill a small lizard or a mouse. Food is mainly detected by touch through the antennae and legs. In contrast to millipedes, which have no need to move fast, centipedes have longer legs, and move quickly to hunt and seize prey. There are about 2,500 species in existence.

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IT’S A FACT Centipedes and millipedes can live a surprisingly long time. Centipedes can live six years or more, and millipedes live more than ten. A different view (left) The underside of this millipede shows its large number of legs.

Giant African millipede (below) Although huge in comparison with other species, this is a harmless plant eater. © DIAGRAM

Poison claw

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Invertebrates

Springtail

Flea

Silverfish

Proturan

Velvet worm

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NSECTS ARE THE MOST SUCCESSFUL of all land arthropods in terms of numbers and variety of ways of life. Most fly well, but several groups of primitive wingless insects are earthbound. Some insects have become wingless because they have no need of flight, as they live inside plants or burrow in the ground. Fleas, which are parasites on other animals, are wingless. There are other arthropods living on land, but none rival the insects in number. Crustaceans, such as shrimps and crabs, are extremely successful in the sea, but few of the 50,000 species live on land. Some crabs do so, but most of these live near coasts and return to the sea to spawn. The coconut crab of the Pacific islands is a spectacular creature. Related to hermit crabs, it climbs trees and can open coconuts.

Like spiders, millipedes and centipedes, insects have jointed legs. Invertebrates with such legs are known as arthropods.

Coconut crab This crab grows up to one foot (30 cm) long, and may weigh nine pounds (4 kg).

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IT’S A FACT Woodlouse eggs hatch directly into small woodlice, without the aquatic larval stage found in most crustaceans. The eggs are kept in a liquidfilled pouch inside the mother until they hatch. Woodlice are successful land crustaceans. They belong to a group called isopods. Most isopods crawl or swim in the sea, where one species reaches 17 inches (42 cm), but most woodlice are only o.4 inch (1 cm) or so long. Woodlice have gills, but many also have breathing tubes like those of insects. These help reduce water loss in breathing, but most woodlice still live in damp places and are active at night, as their skins are not waterproof. Woodlice feed on dead and living plants. Bacteria in the gut help to break this food down. There are only 80 species of velvet worms. Attractively colored in blue, green, or orange, and with a velvety sheen, they are nocturnal and shun strong light. They live on forest floors and other damp places in the tropics. Few are more than 6 inches (15 cm) long. They walk using a pair of legs on each body segment, and prey on small animals. The jaws and antennae are reminiscent of insects and other jointed-legged animals, as is the habit of molting the skin periodically. They have breathing tubes and a blood system like that of an insect. On the other hand, their legs are not jointed and much of the body is rather like that of a worm. At one time, they were thought to be intermediates in evolution between worms and insects, but their exact relationship is uncertain. Early velvet worms lived in the sea 500 million years ago.

Flea’s head (below) This is a greatly enlarged drawing of the head of a bloodsucking flea.

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Frogs and toads

Both frogs and toads have unusual shapes for a vertebrate. Cane toad (right) One of the largest land amphibians, it is now a major pest in Australia. Triadobatrachus

Frog Skeletons (above) Frogs have a very short backbone. The fossil (top) shows the beginning of this trend.

Surinam toad (right) This creature is entirely aquatic.

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HE SKULL, HEAD, AND MOUTH of a frog or toad are relatively large. The back legs are long, and most species can straighten them suddenly to leap. The body is short, with nine or fewer vertebrae, no ribs, and hip bones that are large and rigidly joined to the backbone. These are adaptations for jumping. The shorter front legs act as shock absorbers. Frogs are meat-eaters. The large eyes help them to find prey. Muscles also pull the eyeballs down to help in the process of swallowing. The earliest known froglike amphibian is Triadobatrachus, from 220 million years ago. Soon after, frogs took on their modern shape. Their great success, though, seems to have come in the last 65 million years. There are about 3,500 species of living frogs and toads. They range in size from adults only o.4 inch (1 cm) long to the Goliath frog of West Africa, which can grow up to 14 inches (35 cm) long. Some frogs and toads burrow. Others live on the surface. Some are good tree-climbers, and others always live in, or around, water. All have moist, scale-less skins, one reason why most live in damp places and are active at night. Many have glands in the skin that secrete substances that deter attackers. In some cases, as in poison-arrow frogs, the secretion is deadly poisonous.

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ON THE LAND AMPHIBIANS AND REPTILES

Amphibians typically lay eggs in water. These are fertilized externally and hatch into aquatic larvae with gills. These later turn into adults that live on land, breathing air with lungs and through the skin. Some may lay as many as 10,000 eggs, allowing for great losses at the egg and tadpole stage. But there is a surprising variety in frog reproduction. Some poison-arrow frogs guard their eggs on damp ground until they hatch, then carry them to water attached to their bodies. Other frogs beat a body secretion into a mass of foam on a branch above the water and deposit their eggs in it. The tadpoles later fall into water. Yet other frogs carry eggs or young in skin pouches of various types. Surprisingly, a fifth of all frogs lay eggs on land that develop straight into little frogs.

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STRANGE BUT TRUE Darwin’s frog swallows eggs into its vocal sac and keeps them inside until they have developed into adults.

Poison-arrow frog (left) This creature transports its tadpoles on its back.

© DIAGRAM

Bug-eyed tree frog (left) Large toe-pads and big eyes are adaptations that help tree frogs to climb more easily.

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Salamanders

Tree-climbing salamander (below) This lungless salamander is a good climber.

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N GENERAL, SALAMANDERS probably look much like some of the earliest tetrapods hundreds of millions of years ago. In many ways, though, they have changed compared to these remote ancestors. Only about 350 species of salamander are alive today, nearly all living north of the equator. They are most abundant in North America. Tennessee is said to have more kinds than the whole of Asia and Europe. Some salamanders have reverted to a permanently aquatic life, but most are land animals, 6 inches (15 cm) long or less. They feed on small prey such as insects, worms, and slugs. Because of their thin, moist skins, salamanders live in damp places. Many spend a large part of their lives doing nothing, hiding in burrows or under stones or logs.

Salamanders and newts are amphibians with long bodies, long tails, and small heads. They have two pairs of short legs sticking out sideways from the body. They walk flexing the body from side to side.

Catching insects Some salamanders catch prey by shooting out their long tongues.

Terrestrial salamander (above) This salamander lives on the ground and also in burrows.

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ON THE LAND AMPHIBIANS AND REPTILES

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IT’S A FACT Some caecilians have aquatic larvae, and some hatch from eggs as miniature adults, but many known species give birth to live young. The babies inside the mother’s body are nourished with special secretions when the egg yolk is exhausted. Newts move to water in spring, where they court and mate before laying eggs that hatch into larvae. These feed in water before changing into the adult form. Adults spend most of their time on land. A few salamanders lay eggs on damp land or even produce living young. On land, salamanders and newts breathe through the skin, the mouth lining, and the lungs. Lack of lungs might be thought a handicap in an air-breathing animal. However, the 200 species in the biggest family of salamanders are entirely lungless. They are mostly small, and absorb enough oxygen through their skins. Many are skilled hunters, and can shoot out a long tongue to trap an insect. The caecilians are strange amphibians, close to neither salamanders nor frogs. They burrow through the soil, have no limbs, and have very reduced eyes. They look like earthworms, complete with rings, and feed on worms and insects. In size they range from 4 to 28 inches (11 to 70 cm). They have very solid skulls, which help them push through the soil. Many aspects of their lifestyle remain unknown.

Taking it easy Salamanders have an inconspicuous lifestyle but, in some places, make up a large part of the local animal life.

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Early reptiles

Hylonomus This was one of the very first reptiles.

Seymouria Reptiles may have evolved from tetrapods “early amphibians” like this one.

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NE GROUP OF “TETRAPODS,” including Seymouria and its relatives, had strong legs that held the body off the ground. Seymouria was a 24-inch-long (60 cm) animal that lived about 280 million years ago. Some aspects were quite reptilian; in fact, they were once thought to be reptiles. However, the skull still had lateral line grooves. In fishes and amphibians these hold sense organs for feeling movement in water. Fossil aquatic larvae have also been found, so these were not yet reptiles, but possibly the group from which the reptiles evolved. The next great innovation was the shelled egg, allowing reptiles and synapsids to be full-time land animals. The shell, either hard or leathery, gave the embryo its own private pod in which to develop. Membranes surround the embryo to protect it, and allow it to breathe. Unfortunately, fossil eggs and skin, characterized by scales, are rare. This means that we have to distinguish between fossil reptiles and non-reptiles by their bones and, in particular, the skull. The earliest animal recognized as a reptile is a little creature called Hylonomus that lived about 310 million years ago in what is now Nova Scotia. About 8 inches (20 cm) long, it was shaped like a lizard, although it was not closely related. Its small head had the small sharp teeth of an

Soon after tetrapods became established on land, some became even better at living on land than in the water.

ON THE LAND AMPHIBIANS AND REPTILES

insect-eater. After this reptiles evolved rapidly. Some remained small, while others were bulky animals. Many stayed as insect or flesh-eaters, but others had teeth that were adapted for eating plants. Pareiasaurs were heavy, with massive legs to support their weight. They reached 8 feet (2.5 m) long or more. They had leaf-shaped teeth, like modern planteating lizards.

The pelycosaur group This group of synapsids included both plant-and meat-eaters. Meat-eaters such as Dimetrodon had long skulls, and their teeth were adapted for biting. They had long fanglike teeth at the front of the jaw. Plant-eaters, such as Cotylorhynchus, had short jaws with peglike teeth all round. Some pelycosaurs grew more than 10 feet (3 m) long. These early synapsids died out well over 250 million years ago.

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Pareiasaurus First inhabitants Pareiasaurs, up to 5 feet (2.2 m) l0ng, were some of the first large planteaters on the land.

Dimetrodon (left) This creature had teeth specially adapted for catching prey.

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Cotylorhynchus (above) Weighing as much as a cow, this was a very early plant-eater.

© DIAGRAM

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IT’S A FACT Some pelycosaurs had a “sail” of skin on the back, supported by long projections from the spine, some as much as 60 inches (1.5 m) long. This sail may have helped the animal collect heat from the Sun by leaning sideways toward it. By changing position it may have been able to regulate its temperature. How did pelycosaurs without sails manage?

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Rise of the dinosaurs

Dinosaurs evolved about 235 million years ago, probably from small reptiles like Euparkeria. Little over 20 inches (50 cm) long, this predator had teeth in jaw sockets, which was a standard feature for dinosaurs.

D

INOSAURS rapidly became the dominant large land animals, and remained so until 65 million years ago when, with the exception of birds, they became extinct. During that time many different dinosaurs evolved and disappeared, succeeded by new kinds. They had different body shapes, different sizes, and adaptations to many different ways of feeding. But the thing that probably began their success was quite simple. The dinosaurs had a thighbone with a ball-like projection sticking out at an angle at the top. This fitted snugly into a socket in the hip bones, and allowed them to use their legs in a vertical position right underneath the

Tyrannosaurus rex (above) This was a huge, meateating dinosaur. Scientists differ over how fast it could move.

Coelophysis (right) This was an early, small, bipedal dinosaur.

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ON THE LAND AMPHIBIANS AND REPTILES

body. They could easily be swung back and forth when walking or running. In most reptiles the legs stick out in a sideways position. These improved legs were also good at supporting weight. Some of the dinosaurs were much heavier than any land animals before or since. Others were small, lightly built, and good runners. Many of the earliest dinosaurs had hind limbs bigger than the front ones, and were undoubtedly bipedal. Later, heavier dinosaurs tended to support their weight on four limbs, but many dinosaurs remained bipedal. The huge meat-eater Tyrannosaurus rex, weighing six tons, had tiny arms and was bipedal. Most scientists recognize two divisions within the dinosaurs. The first includes the “lizardhipped” dinosaurs, or saurischians. The earliest known dinosaurs belong to this group. Saurischians include various carnivorous types, and also one major group of plant-eaters, the sauropods. These had huge bodies on elephantlike legs, and long necks and tails. Their heads were comparatively small. They tore off plants with their teeth then swallowed them into a gizzard, where they were ground with stones, as in a bird. Sauropods included such familiar dinosaurs as Diplodocus and Apatosaurus (Brontosaurus).

IT’S A FACT For many years Brachiosaurus was the largest known dinosaur, at up to 90 feet (27 m) long and 80 tons (tonnes) in weight—as much as 20 large elephants. Now bones of even larger sauropods are known, such as Argentinosaurus, maybe 115 feet (35 m) long and up to 100 tons (tonnes) in weight. Seismosaurus was even longer, but not so heavily built. Most giant dinosaurs are only known from a few bones, so relative size is estimated by making a comparison with better-known animals.

Adapted for feeding Camptosaurus and its relatives may have had tongues that could pull plant food into their mouths.

© DIAGRAM

Brachiosaurus One of the biggest-ever dinosaurs, this creature had very long forelimbs.

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Dinosaurs in variety

The dinosaurs that are not “lizard-hipped” are “birdhipped” or ornithischian.

Maiasaura This creature laid eggs in mud nests within a protective rim.

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HE BIRD-HIPPED DINOSAURS were, with no known exceptions, plant-eaters. They were the main herbivores toward the end of the dinosaur age, when the giant sauropods had disappeared from many parts of the world. The ornithischians include familiar animals such as Stegosaurus, Iguanodon, and Triceratops. Iguanodon was one of the most widespread dinosaurs, and its remains have been found in North America, Europe, and Asia. It had a toothless beak, but many cheek teeth to break up its food. The warm climate and plentiful food allowed herds to flourish. Many of the plant-eaters, from the giant sauropods to Triceratops, seem to have been herd animals that found safety in numbers. Some duck-billed dinosaurs were able to deal with really tough food such as pine needles. Behind the toothless bill was a huge battery of grinding teeth. New teeth constantly grew from below, replacing the ones that ground down. A duckbill could have 2,000 teeth, the highest number in any backboned animal. A surprising amount is known about breeding in one Iguanodon

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ON THE LAND AMPHIBIANS AND REPTILES

duckbill, Maiasaura. A whole fossilized breeding colony was discovered with eggs and young in mud nests shaped like little volcanoes. A large number of ornithischian dinosaurs were ankylosaurs. Not as large or spectacular as some dinosaurs, they were nevertheless successful animals. They had small teeth and probably fed on soft plants. Their notable feature, and probably what made them successful, was body armor. Bony plates covered their backs and bony spikes, covered with horn, added extra protection. Some had a bony club on the end of the tail as an extra defense. The bird-hipped plant-eaters were hunted by meateaters, all of which were lizard-hipped dinosaurs. They ranged from the enormous Tyrannosaurus rex to fast runners such as Velociraptor and Deinonychus. The latter was about 10 feet (3 m) long and had an enormous killing claw on its hind foot. Smaller still was Saurornithoides, which lived about 80 million years ago. It had a large brain, large eyes that could judge distances as it pounced on small creatures, and it may have hunted at night.

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IT’S A FACT Pachycephalosaurus and its relations had very thick, bony heads. They may have been used in head-clashing rivalry between males, rather like modern goats. Although the thick bone prevented damage, it left little room for a brain.

Stegosaurus

© DIAGRAM

Triceratops

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Tortoises and tuataras

Proganochelys From about 200 million years ago, this creature already had an armored outer shell.

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NE LINE OF AMNIOTES developed a single main skull opening. Early amniotes included the ancestors of reptiles and synapsids. These synapsids are all extinct, but we and other mammals are their descendants. Most reptiles had two main openings in the side of the skull that made it lighter, and gave space for bigger jaw muscles.These diapsid reptiles included many extinct types, such as non-bird dinosaurs. Snakes and lizards are living diapsid reptiles. The first fossils of the tortoise group come from over 200 million years ago. They were already very similar in structure to those of today. There is little clue to their immediate ancestors. Tortoises have scales, and solid shells like early reptiles. They lay shelled eggs on land. They have unusual bodies; the shell has an outer horny layer equivalent to the scales, with an inner layer of bone. This is made from bony plates in the skin plus the ribs and backbone. All these fuse together to make a strong box. The hip and shoulder bones end up inside the ribs, rather than outside. As they cannot move their ribs, tortoises have special muscles to fill their lungs. There are no teeth, just a horny beak. The shell is good protection, but limits mobility.

The skull of the earliest reptiles had solid bone along the sides and over the top, except for eye sockets and nose. The only living reptiles with this type of skull are the tortoises and turtles.

Anapsid skull

Anapsids (left) Apart from those for eyes and nostrils, anapsid reptiles lack holes in the sides of the skull.

Tortoise shell and skeleton

ON THE LAND AMPHIBIANS AND REPTILES

Land tortoises are usually slow-moving vegetarians. Some are not much more than 4 inches (10 cm) long when fully grown, but the giant tortoises of the Indian Ocean and Galapagos islands may be 4.5 feet (1.4 m) long and weigh 550 pounds (250 kg). The tuatara is the sole relic of a group of diapsid reptiles that were widespread over 200 million years ago. Tuatara Now it lives only on This creature now islands off the coast of only survives on a New Zealand. The tuatara few small islands. itself has hardly changed in 140 million years. Its slow-motion life is interesting: it can be active at cooler temperatures than most reptiles, and its eggs may take 15 months to hatch.

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IT’S A FACT Tuataras can live for 100 years. Spurthighed tortoises and box turtles can also live for 100 years or more. A Seychelles tortoise, possibly 50 years old at the time, was taken to the island of Mauritius and lived there for a further 152 years.

© DIAGRAM

Seychelles giant tortoises Giant tortoises live only on islands free of major land predators.

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Lizards

“Tasting” the air (above) The Komodo dragon uses its long, forked tongue to “taste” the air.

Threat gesture The frilled lizard of Australia spreads its frill as a threat to potential enemies.

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HE BIGGEST LIVING LIZARD is the Komodo dragon from Indonesia which is 10 feet (3 m) long. The smallest is a West Indian gecko which is 0.75 inch (1.8 cm) long. Typical lizards have a long body and tail, and legs extending sideways from the body. Many kinds can break the tail off if attacked. They leave the wriggling tail as a decoy, and grow a new one later. Lizards mostly have good eyesight and color vision. Holes at the side of the head mark the position of the ears. The tongue is another important means of sensing their surroundings. In the roof of the mouth is Jacobson’s organ. This is sensitive to chemicals gathered on the tip of the tongue from outside. Lizard scales may be anything from granules in a soft skin to tough overlapping plates. In some species, such as the spiny-tailed lizard, they are developed into sharp spines for defense. Most lizards eat insects or other animals. A few, such as iguanas, eat plants. There are many variations in lizard body shape and adaptations. Monitor lizards are mostly

Lizards evolved some 200 million years ago. There are more than 3,500 living species: most are small animals living in warm regions of the world.

Komodo dragon hatching Most lizards, such as the Komodo dragon, lay eggs.

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ON THE LAND AMPHIBIANS AND REPTILES

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DID YOU KNOW? Few lizards make sounds other than hissing. They rely on colors and visual signals to communicate. Geckos, however, are mostly active at night, and communicate with a surprising range of clicks and chirping noises. Close up (above) The ridges beneath a gecko’s toes are clearly visible when it clings to a glass surface. Chameleon (below) This creature is famous for its ability to change both color and pattern to suit its surroundings.

© DIAGRAM

large, with a long neck and short body. They have strong legs and claws, and are powerful carnivores. At the other extreme are the slow worms, with smooth shiny skin and no legs. This is a pattern adopted by many burrowing lizards. Green iguanas climb using their long toes and claws to grip, and a long tail to help them balance. Some climbers are more specialized. Chameleons have hands and feet that allow two digits to fold the opposite way round a branch to the other three, providing a strong grip. Their tails also grip. They move slowly to stalk prey, and then shoot out a sticky tongue as long as their body. Geckos have feet with ridges under their toes. On the ridges are tiny projections which can grip surfaces as smooth as glass. They can run up walls, upside-down on ceilings, and of course up rocks and trees with ease.

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Snakes

Black Mamba This is a fastmoving, African snake that belongs to the cobra family.

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SNAKE’S BODY is enormously elongated, with a single lung and other organs, such as kidneys, which are very narrow and placed one behind the other. It appears to be a restrictive body shape, but snakes live in a variety of habitats. Some live on dry land, some burrow underground, and others climb. The jaws and skull of a snake are incredibly flexible, and the jaws can spread wide. The two halves of the bottom jaw can “walk” around prey held in the mouth. The ability to grasp and swallow an enormous meal makes up for having no limbs. Snakes may go for a long time between meals. Like lizards, they periodically shed their skins, often in one piece, leaving a shiny new one. The earliest snakes evolved from lizards 130 million years ago. They appear to have been constrictors. Later types developed venom to overpower their prey. Pythons and boas seize their prey, and then crush it with their coils, suffocating the animal they have caught. They have no venom. This is also true for most of the large family which includes grass snakes. Some constrict their prey, while many grab and swallow frogs or small mammals.

With nearly 2,500 species, snakes are a successful group of modern animals. Snakes have no legs, although some of the more “primitive” kinds, such as pythons, still have tiny remnants.

A hearty meal A python may swallow an animal as large as a deer.

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ON THE LAND AMPHIBIANS AND REPTILES

Indian cobra When threatened, this snake responds by spreading the hood of its neck.

A few of this family have small fangs in the back of the mouth. Venom glands open nearby. When the snake bites, the poison helps to subdue prey. Most back-fanged snakes are not dangerous to man. The cobras and their relatives have larger venom glands, and these are connected to short fangs at the front of the jaws. The fangs have grooves down which venom flows. Cobra venom works on the nervous system, paralyzing prey. Vipers and rattlesnakes also have front fangs, but they are much longer. These fangs are folded in the mouth until the snake strikes. The fangs work as hypodermic syringes to inject venom, which then affects the blood and muscles of the victim.

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STRANGE BUT TRUE Rattlesnakes and pit vipers have an extra sense. A pit on each side of the face can detect heat, allowing them to strike accurately at warm-blooded prey even in the darkness.

What makes a rattle? (below) The rattle of the rattlesnake is made from a chain of horny tail-tips.

© DIAGRAM

Viper skull (below) This skull shows the long, folding fangs typical of a viper.

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First mammals

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BOUT 250 MILLION YEARS AGO there was a great extinction. Some synapsids survived, including the cynodonts. By about 210 million years ago, these were evolving into the first mammals. But, at about this point, the dinosaurs became the dominant animals on land. Mammals lived alongside them, but were comparatively insignificant creatures until all non-bird dinosaurs became extinct. The transition from “reptile” to mammal was not sudden. The cynodonts were rather wolflike in shape. Gradually, over millions of years, they acquired typical mammal characteristics. Some of the differences between typical reptiles and mammals are shown below.

Reptiles like synapsids, the evolutionary line that eventually led to mammals, were the first backboned land animals to become widespread. Successive kinds ruled the world for nearly 100 million years.

Reptile No muscular diaphragm between chest and abdomen Ribs all the way down body Legs sprawl to side Teeth similar along length of jaw Teeth simple in shape Single bone in inner ear Several bones in lower jaw Lay shelled eggs Do not feed young Have scaly skins

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Mammal Muscular diaphragm to help breathing

Long ribs just in chest region Legs brought underneath body Different teeth in different parts of the jaw Teeth complex, with complex roots Three bones in inner ear Single bone in lower jaw Young born alive Feed young on milk from mother’s body Have hair

Early synapsids shared many features with reptiles. In mammals all these changed. For instance, two bones that helped to form the lower jaw became tiny bones in the ear of mammals. Possession of three bones there is often used to define a fossil as a mammal. The change can be seen in developing mammal embryos, and also in fossils.

ON THE LAND MAMMALS

Cynognathus A therapsid synapsid, this creature probably had fur and whiskers.

Thrinaxodon

Oligokyphus

Cynognathus

© DIAGRAM

Some characteristics, such as feeding babies on milk, or having hair, cannot be seen in ancient fossils. However, later cynodonts have skull snouts with grooves and holes where whiskers probably grew, and blood vessels also ran in fleshy lips. Animals with a diaphragm for efficient breathing, plus a coat of hair, were almost certainly warmblooded. Early mammals, though, may not have kept themselves either so warm, or at such an even temperature, as do most mammals today. With improved legs, mammals became more agile. But there was also a trend toward becoming smaller and lighter.

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Egg-laying mammals

Tiny primitive mammals, such as Morganucodon, lived alongside early dinosaurs 200 million years ago. The history of mammals then becomes more obscure. It was unusual for tiny mammals to be fossilized. Sometimes only their hardest parts—their teeth—are left.

Morganucodon Like many of the small early mammals, this creature fed on insects.

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N A FEW PLACES it is possible to sift earth and extract the minute teeth of mammals. Teeth tell part of the story, and may suggest an animal’s lifestyle. Without other bones it is difficult to follow how mammals evolved. We do not know if these mammals had young born alive, or laid eggs. Several, perhaps as many as six or seven, main groups of “mammals” lived alongside dinosaurs. The biggest group are known as multituberculates because they had many “tubercles,” or bumps, on their teeth. They also had large front incisor teeth, and strong jaws. They probably lived like present-day rodents, although they were not related. Some were as big as a marmot— mammal giants for their time. They outlasted dinosaurs for millions of years, but are now extinct. The three living groups of mammals are the monotremes, marsupials, and placentals.

Echidna The echidna is one of the living “egg-laying mammals.”

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Monotremes are egg-layers. Only two types survive: the duck-billed platypus and the echidna. Both are specialized, as well as having primitive characteristics. The echidna has spines on its back; it has toothless jaws and a long sticky tongue for gobbling up ants and termites. It also has strong claws and is a good burrower. It is mainly nocturnal, but is also active by day. The platypus hunts for its food in water. Monotreme bodies burn up energy more slowly than most mammals, and maintain a lower temperature. They lay small leathery eggs. When babies hatch they are still quite undeveloped. The mother feeds them milk, but there are no special Adapted for hunting teats. The mother’s The beak of the platypus milk just oozes on to is covered in sensitive skin the fur from where it is lapped up. that helps it to find food.

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IT’S A FACT Monotremes only live now in the Australian region. Until recently, nothing was known of their history further back than a few million years ago. Now ancient fossils are known. Steropodon is a monotreme that lived 110 million years ago in Australia. It is known from a jaw with teeth. As modern adult monotremes have no teeth, how did scientists know what it was? The answer is that young platypuses have milk teeth. Steropodon teeth were like these. Other platypus fossils have been found, including one from South America. Giant echidnas are also found as fossils.

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Ancient marsupials

Thylacosmilus (above) This was a jaguar-sized, saber-toothed, marsupial meat-eater.

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N SOME MARSUPIALS a pouch is absent and the babies are just carried attached to the mother’s nipples. Later, they may ride on her back. The kangaroo is the animal most people call to mind when they think of marsupials, but they are a varied group with a long history. With one exception, they are today confined to the Australian region and South America. The earliest marsupials known are fossils from about 75 million years ago found in North America. From there, marsupials spread into Europe, but were not greatly successful. Even in North America they eventually died out about 20 million years ago. From then on the northern continents had no known marsupials. However, from North America the early marsupials managed to make the trip to South America. South America was joined at the time to Antarctica and Australia in one great continent, known as Gondwana. Marsupials spread right across it, but the great continent was breaking up. By 45 million years ago, Australia broke off and slowly drifted north. Fifteen million years later, South America broke away from Antarctica and moved north. The climate cooled and Antarctica became

Marsupial mammals have babies born in a very undeveloped state. Many have a pouch (marsupium) in which the young stay as they grow. In the pouch the young attach to a nipple and feed on milk.

Neohelos (below left) As big as a cow, this Australian creature was a plant-eater.

Palorchestes (above) The principal feature of this creature was its short trunk.

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Diprotodon (right) This huge, wombatlike, creature was adapted to grazing dry grasslands.

IT’S A FACT Even just thousands, rather than millions, of years ago huge marsupials roamed Australia. There was a short-faced kangaroo 10 feet (3 m) tall, and Diprotodon, a four-legged plant-eater as big as a rhinoceros. This is the largest known marsupial. Procoptodon (below) This creature was the largest kangaroo known in Australia thousands of years ago.

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frozen. But a fossil marsupial about 40 million years old has been found there, showing it was once populated. From the original ancestors, evolution produced different sets of marsupials in isolation in South America and Australia. The ones that remain in Australia are extremely varied, but none is larger than a red kangaroo. In South America few living marsupials are bigger than a large rat. This was not always so. Some 25 million years ago marsupial meat-eaters larger than leopards were hunting in the region. Borhyaena was a powerful beast, and Thylacosmilus was a saber-toothed marsupial long before saber-toothed cats existed. In recent years Australian fossil deposits 55 million years old have been examined and marsupials unearthed. One small animal belongs to a family otherwise known only from South America. There are insect-eaters, an ancient bandicoot, and other strange forms.

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Carnivorous marsupials

In South America there are over 80 species of opossum. Most feed on insects or other small prey, but top up their diet with fruits and other plants. Most are small and mouselike. Some are as big as a cat. Most species are good climbers. Many have forwardfacing eyes and good vision.

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Numbat This creature is a specialized insect-eater.

A Virginia opossum This marsupial carries its young on its back.

ONTRARY TO THE IDEA THAT MARSUPIALS are “failures,” they are a successful group with many species. One species, the Virginia opossum, has spread into North America and, in the last century, has moved north as far as Canada. There can be up to 56 young in a litter. In Australia, there are over 70 species of carnivorous marsupials of various families. The biggest family, the dasyures, contains mostly mouse-sized animals. Marsupial “mice” are fierce predators that pounce on grasshoppers and small lizards. Larger species, called quolls, or native cats, also feed on insects and some vertebrates. The biggest dasyure is the Tasmanian devil, an animal that grows up to 32 inches (80 cm) long, plus a tail that is 12 inches (30 cm) in length. It can catch large prey, but often eats dead animals, swallowing chunks of carrion and crunching up bones with powerful teeth. The bandicoots are another family of carnivores. Despite a rabbitlike shape, most feed on insects. The numbat specializes in termites. About 10 inches (25 cm) long, plus a tail that is 7 inches (18 cm) in length, it licks up termites with its long, sticky tongue. The numbat has 52 teeth, more than most other land mammals.

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STRANGE BUT TRUE The gestation period in some bandicoots—under 13 days—is the shortest of any mammal. The baby crawls into the mother’s pouch, which faces the rear, as in many marsupials.

Tasmanian wolf This creature became extinct during the last hundred years.

Bandicoot (above) This creature sometimes burrows with its nose in the soil for insects. © DIAGRAM

Some marsupials look like, and behave like, non-marsupial animals. A marsupial mole, with powerful claws and a smooth coat, tunnels to search for insect larvae. In spite of differences in detail, the resemblance to true moles is striking. The thylacine, or Tasmanian wolf, was another good example of convergence between species. It was the size and shape of a dog, and could trot long distances to run down prey, such as wallabies. Because settlers thought it would attack sheep, it was hunted to extinction. The last thylacine died in a Tasmanian zoo in 1936.

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Kowari (above) Although it looks like a mouse, this creature is a predator.

Tasmanian devil (right) The main feature of this creature is its ferocious set of teeth.

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Plant-eating marsupials

Looking after its young (right) After birth, a kangaroo “joey” may spend several months in the pouch of its mother.

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ANGAROOS have a welldeveloped pouch providing a home for the young “joey” from the time when it crawls there after birth until it is large and mobile. There may be a well-grown joey going to the pouch for protection and milk at the same time as a tiny joey is born and fixes to a nipple. The mother produces different milks from different nipples for both of them. Soon after mating, the fertilized egg in the mother may stop developing. It resumes development when needed as a replacement for a joey that becomes independent, or dies in the pouch owing to its poor physical condition. The red kangaroo, the largest, can grow to 65 inches (1.65 m), with a tail 40 inches (1 m) in length. At speed, with bounds of up to 30 feet (9 m), they may travel at nearly 31 miles per hour (50 kmph). At the other extreme are rat kangaroos 10 inches (0.25 m) long, with a tail 6 inches (15 cm)

Over 100 species of plant-eating marsupials inhabit the Australian region. About half are varieties of kangaroo. Unlike carnivorous marsupials, with many incisor teeth at the front of the mouth, the plant-eaters just have two incisors in the lower jaw.

Wombat (above) This creature is well-known for its ability to burrow.

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in length. Kangaroos are mainly active during the evening and at night. Most feed on grasses. Some smaller ones eat roots. A system of bacterial fermentation of plants occurs in the stomach similar to that of sheep. The different species live in various habitats. Possums and cuscuses are roughly cat-sized, feed largely on leaves, and climb with dexterity. Cuscuses live mainly in New Guinea, and have prehensile tails. The common brushtail possum lives in many habitats, including gardens, where it can be a pest. Ringtail possums are medium-sized climbers with good claws and opposable big toes for grip. They feed on leaves, and the cecum in the gut is enlarged to help digestion. Other small possums feed on gum oozing from trees, or on nectar from flowers. The tiny honey possum weighs only 3.5 ounces (10 g). Its long snout holds a long tongue tipped with bristles to lick up nectar. The wombat is a heavily-built burrower that is active at night. It feeds on tough low-grade grasses and roots.

Honey possum This is one of the tiniest marsupials.

Cuscus The coiled tail of this creature can help it to grip branches whenever necessary.

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IT’S A FACT The koala has a specialized diet of eucalyptus leaves. The leaves are tough and full of oils and poisons, but the koala has a gut that can deal with them. Although koalas climb tree trunks with their heads facing upward, the female koala’s pouch faces backward.

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Primitive placentals

The embryo of a rabbit (above) The embryo is attached to the mother’s body by a plate of tissue that is called the placenta.

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LACENTAL MAMMALS are mostly found in Europe, Asia, Africa, North, and even South America. However, in the Australian region, placentals are a minor part of the fauna with only bats and rodents, comparatively recent arrivals, well represented. The usual explanation is that placentals were unable to cross the sea to Australia, preventing them pushing aside the “primitive” marsupials. However, fossil mammal jaws unearthed in the 1990s in Australia are from primitive placental mammals living 115 million years ago. From deposits 55 million years old, with Australia already an island, remains of a primitive placental called a condylarth were unearthed. In deposits 25 million years old there are plenty of marsupials, but no placentals. Perhaps the story needs to be reversed, with marsupials having pushed aside placentals in Australia. Placental mammals have their young born in an advanced state. The babies are joined to the mother’s womb by the placenta. This disk of intermingling tissue allows nourishment to be transferred along the umbilical cord. The time in the womb may be long: nine months in humans, and over a year in elephants. Babies may be much larger and better developed than are marsupial newborn.

Typical mammals today— from rats and mice to bears, tigers, and elephants— are placental mammals.

Zalambdalestes This was an early insecteating placental mammal 8 inches (20 cm) long.

Distribution of monotremes

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The system can also be tuned to the habits of the animal. Antelope young can be born ready to stand and even run. Animals with a nest or den, such as mice or bears, may produce small, blind, and naked young. Apart from reproduction, there are many other differences between placentals and marsupials in skeletal details and other body parts.

Eomaia This is the earliest placental mammal.

Distribution of placentals

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IT’S A FACT The history of placental mammals before 80 million years ago was at one time only known through fossil teeth. Then, in 2000, fossils were dug from a 125 million-year-old fossil lakebed in China. As well as dinosaurs, they included a mammal. A complete skeleton, plus fur and some internal organs, were found. The teeth and ankle-bones of Eomaia mark it as the earliest known “placental” mammal. We do not know whether this animal, 5 inches (13 cm) long, actually had a placenta. Its hips look too small to give birth to large babies, and it may have produced tiny young like a marsupial. It was an insect eater and a good climber.

Distribution of marsupials

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Insectivores

Around the world there are still many small mammals which are insect-eaters like early placentals. They typically have pointed snouts and many sharp teeth. They have short limbs with five clawed toes on each. The brain is not very large.

Mole (below) and starnosed mole (below right) The mole catches worms to eat. It sometimes immobilizes them with a bite. The “star” of the starnosed mole is sensitive to electrical stimuli.

Long-eared hedgehog This creature lives in the deserts and steppes of western Asia.

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SUALLY GROUPED TOGETHER as insectivores, insecteaters are not necessarily closely related to one another. For example, the tenrecs of Madagascar are superficially similar to hedgehogs, but molecular and other evidence suggests they have a separate ancestry. Shrews are widespread, and have been around for over 50 million years. They are small, active, and ferocious, running through the leaf litter and surface tunnels to catch small prey. Most are territorial, driving other shrews from their hunting ground. They need to feed day and night, and may consume their own weight in food in 24 hours. Hedgehogs live in Africa, Europe, and Asia. Spiny fur gives protection, and some species curl into a tight ball if alarmed. Moles live underground, traveling through tunnels and catching worms. Their blunt heads, smooth fur, spade-like hands and strong muscles adapt them for burrowing. Moles live in North America, Europe, and Asia. The whiskery,

Mole

Star-nosed mole

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Striped tenrec (right) This creature erects the spines on its neck if frightened.

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fleshy nose is a good sense organ; in DID YOU the star-nosed mole, it fans out into KNOW? fleshy lobes. The Etruscan In Africa a separate family, the golden pygmy shrew moles, have many of the same is the smallest adaptations. They appear very like the terrestrial marsupial mole,but are not related. mammal, They are another example of weighing only a convergence—looking alike because fraction of an they have a similar lifestyle. The eyes ounce when it are vestiges, and the tiny ears are is fully grown. buried beneath the fur. A leathery pad on the nose helps to push earth out of the way. Tenrecs only live in Madagascar, although 25 million years ago they were found on the African mainland. They include animals that are shrew-shaped, others that are hedgehog-like in appearance, and some that could be described as untidylooking, and unlike anything else at all. They catch a variety of insects and other small creatures. Solenodons live only in Cuba and Haiti, remnants of a group once more widespread in North America. Up to 12 inches (30 cm) long, they are nocturnal, with good senses of touch and scent. They also have powerful scent glands. Like some shrews, they have poisonous saliva.

Solenodon This creature uses its nose to burrow for food in the earth and rotten wood.

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Edentates

The edentates —“without teeth”— are a group of South American mammals that includes anteaters, armadillos, and sloths. Only the anteaters are, in fact, toothless.

Giant sloth (below) The biggest ground sloths were 20 feet (6 m) long. Fossil skin, as well as bones, have been found.

Tree sloths Tree sloths adapt for life upside down.

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HE GIANT ANTEATER lives on the ground. It has powerful claws for digging up ants, and a long, sticky tongue for trapping them. It may eat 35,000 ants a day. Its long jaw contains no teeth. The tamandua is a smaller, treeclimbing anteater that searches out termite nests in the trees. It has a prehensile tail, as does the smallest member of the family, the silky anteater, with head and body about 10 inches (23 cm) long. All have good claws which are used to break into nests, and for defense. Armadillos have armor plating in the form of bony nodules in the skin of the back. Some can curl up into an armored ball when attacked, but most species dig to escape trouble, and may block the burrow with their armored back. They feed on insects, small animals, and

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IT’S A FACT Edentates are thought to have originated in South America, and stayed there, except for a few members that recently moved into North America. A tamandua-like, fossil “anteater” that was found in Germany is not now thought to be an edentate. Tamandua (above) The long jaws of the tamandua contain no teeth, just a long, sticky tongue.

Hairy armadillo (below) This creature lives in open country, and is sometimes hunted for food.

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carrion, fruits, and roots. They often dig for food. The teeth are simple, peglike structures. Armadillos range from the fairy armadillo at 6 inches (13 cm) long, to the giant armadillo at 40 inches (100 cm) long. Millions of years ago, giant 10-foot-long (3 m) plant-eating armadillos also lived in South America. When North and South America joined about three million years ago, some giant armadillos moved north, but all are now extinct. Sloths are adapted for life in the trees, and hang upside-down on huge, curved claws. They move slowly and feed on leaves and buds. The fur has grooves that often contain algae, giving the animal a green tinge that helps disguise it. Everything sloths do is in slow motion, but they are successful animals, often making up a large part of the mammal life of the forest. They maintain a lower and more variable body temperature than most mammals. Tree sloths are not known from the fossil record, but giant ground sloths as big as elephants were once an important part of the fauna. In some places they survived alongside early humans.

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Primates

Tamil loris (above) This is a slow, nocturnal climber from southern Asia.

Ring-tailed lemur (right) This creature uses its tail for balance and signaling.

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ECAUSE HUMANS belong to the order known as Primates, we like to think of the species as advanced, but in some ways it is old-fashioned. For example, primates have generally kept the five fingers and toes of the earliest mammals, and not all have large brains. Primates as a group are climbing specialists. Some climbing adaptations proved useful, when our ancestors started living on the ground, in developing intelligence and manipulating our surroundings. Five fingers and toes are useful for grasping branches. In many primates, claws have changed into flat nails backing a fleshy fingertip that helps in grasping. In most, thumbs and big toes fold around a branch opposite to the other digits to improve the grip. In “lower” primates, the sense of smell is good, but in most primates vision has become the main sense. Two forward-facing eyes give overlapping vision, allowing them to judge distances as they climb or jump. Primates, particularly monkeys and apes, are social animals that live in groups and communicate with one another by means of sounds and gestures. Like those of most forest animals, primate fossils are rare. Occasional finds allow us to trace primates back over 55 million years. The earliest primates to be successful were lemurs. Fossils have been found on several continents, though lemurs are now confined to Madagascar. Most are arboreal climbers and jumpers. There are two main types of monkey, with a long separate history. South American monkeys have wide-spaced nostrils and often a prehensile tail. All are arboreal. Monkeys of Africa and Asia have nostrils close together like ours. Tree-

The primate order includes humans, apes, monkeys, bushbabies, and lorises.

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dwellers have long, but not prehensile, tails for balance. Others such as baboons live on the ground in open country. Some monkeys have specialized diets—for example, colobus monkeys eat leaves—but many are opportunists including fruits, buds, insects, and much else in their diet. Gibbons are the smallest apes. Tailless, like other apes, they swing on long arms through Southeast Asian forests. They use calls to communicate. In Borneo and Sumatra live orang-utans. They are large and heavy, but good climbers, and like the gorillas of central Africa, they are largely vegetarian. The two species of chimpanzee are also African, and are probably our closest relations.

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Spider monkey This American monkey has a prehensile tail.

STRANGE BUT TRUE Tarsiers are small, large-eyed primates from southeast Asian islands. They show similarities to some of the earliest primate fossils. In some tarsiers, just one eye is bigger than the whole brain.

Gorilla This is the largest of all the primates.

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Rabbits and rodents

While rabbits have similarities with rodents, such as rats, they evolved from different ancestral lines. However, recent genetic evidence found in the two groups suggests that, far back in time, they are both on the same main branch of the mammal family tree, together with our relations, the primates.

Jack rabbit Although called a rabbit, this creature is, in fact, a hare. Like other hares, the jack rabbit has long ears and lives in the open rather than in a burrow.

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ARLY RODENTS, looking like small squirrels, are known from 55 million years ago. By 25 million years ago, most of the main types we know today had evolved, although the most successful present-day rodents, the mouse family, do not appear until about 7 million years ago. The history of the rabbit group also stretches back over 55 million years. Rabbits and rodents have specialized teeth for dealing with tough plant food. They have ever-growing incisor teeth at the front of the jaw. These gnaw at plants to break through bark or hard seed coats. There are no canine teeth, leaving a gap in the jaw which can be sealed by drawing the lips across. Food is taken into the cheek region, and ground up by strong, complex teeth. One feature that distinguishes the rabbit group from rodents is that rabbits have two incisor teeth at the top on each side, whereas rodents have only one. Rabbits are found on all continents, even Australia. The European rabbit was introduced there by humans and became a devastating pest. The rabbit family contains 44 species. The biggest, the European hare, has a head and body length up to 30 inches (75 cm), and a weight of 11 pounds (5 kg). The smallest, the pygmy rabbit of North America, is 10 inches (25 cm) long and weighs 10 ounces (0.3 kg). Rabbits

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STRANGE BUT TRUE Rabbits and pikas feed on their own feces, extracting extra nourishment from the same food by passing it through the gut twice.

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are burrowers, although some can put on a swift turn of speed to escape danger. Their claws are strong, but not obviously modified for digging. Hares have long legs, and are adapted for life on the land surface. They use camouflage for protection, but are able to flee very quickly from danger. There are 14 species of pika that live in eastern Asia and northwest America. These have short legs and short, rounded ears. All are smaller than rabbits. Most live in rocky areas, or on steppes. They eat the plants around their burrows. Many kinds cut grasses and leave them to dry, later taking the hay into their burrows to use as winter food.

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Main lagomorph types Hares (right) are large. Rabbits (center) are smaller and often burrow. Pikas (left) are small and most species live in Asian mountains.

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Squirrels

Rodents can be divided into squirrellike, guinea piglike, and mouselike types. They are distinguished, among other things, by the way their jaw muscles are attached to the skull. There are nearly 400 species of squirrellike rodents in Asia, Europe, Africa, and the Americas. They typically feed on seeds and nuts in trees.

Red squirrel The European red squirrel is a typical treeclimber.

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REE SQUIRRELS, such as the red squirrel, are agile climbers. They are light and need little more than sharp claws to climb tree trunks. They run along branches and jump from tree to tree. Pygmy squirrels of Southeast Asia are only 4 inches (10 cm) long, with a 3-inch (8 cm) tail and weigh 1 ounce (30 g). Giant squirrels from the same region are up to 18 inches (45 cm) long, with the same length tail, and weigh 4 pounds (2 kg). As well as tree squirrels there are many others, such as chipmunks, that spend much time on the ground. Marmots are heavily built. They live on the ground and burrow well. Various kinds live high in the mountains of Europe, Asia, and North America. Marmots hibernate during the winter. Many ground-living squirrels make colonial burrows. Prairie dogs are small marmots that make vast burrows. Squirrellike rodents include gliders, and the beaver. They also include the mountain beaver, which is neither a beaver nor necessarily found up mountains. Found in western North America, it burrows well, and usually lives below ground. Small, round, vegetarian animals, mountain beavers are the most primitive living rodents. Pocket gopher This creature is a burrower.

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Pocket gophers are North American. The 30 or so species have compact bodies and little necks. They are burrowers in light soils, and use their front feet and incisor teeth to dig above ground. They feed on roots and plants near the burrows. This turns and aerates soils, but may also damage crops. They are called “pocket” gophers because they have a fur-lined external pocket in each cheek. The springhare is African, looks unlike the other squirrellike rodents, and is lanky with long back legs on which it hops, with the tail balancing the body. The back claws are rather hooflike. The springhare stays in its burrow during the day, and emerges at night to feed on grasses. The head and body are up to 17 inches (43 cm) long, with an even longer tail.

Springhare This creature hops on its hind legs like a kangaroo.

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IT’S A FACT Marmots often hibernate for as much as nine months in any one year.

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Chipmunk This is an attractive ground squirrel.

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Prairie dog

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Mice and guinea pigs

Deermouse (above) This creature has a typical mouse face with whiskers and big, nocturnal eyes.

Long-eared jerboa (right) This creature lives in the deserts of China.

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OME INDIVIDUAL SPECIES of mouselike rodents live in vast numbers. The majority of them are unremarkable to look at, and most are small. Perhaps this is part of the reason for Dormouse their success. They are This creature lives in trees, small enough to enter, and can sleep for six months and use, many different of the year or more. habitats. They are basically seedeaters, but their jaws can adapt to other types of food. They breed fast and are very adaptable; their bodies can climb, burrow, or run on the surface. The Eurasian wood mouse and American deer mouse are typical of this group. The larger members of the group, the rats, mostly live in the wild with no effect on people. A few species are pests, destroying stored food. The black rat is notorious for carrying plague. Some mouselike rodents have taken up burrowing, including blind mole-rats that live completely underground. There are also gerbils (adapted to dry climates), hamsters, dormice (adapted to tree climbing), and jerboas, which live in deserts, and jump on their hind legs. Guinea pig-like rodents mainly live on the continent of South America. Some people question whether porcupines, which can usually be found in North America, Africa, and Asia, really

Of all present-day mammals, mouselike rodents are by far the most numerous. They live in all habitats, and have reached every continent except Antarctica. There are over 1,100 species of them, nearly one quarter of all mammals.

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Capybara This creature is only found in South America.

IT’S A FACT The biggest rodent of all, the capybara, is semiaquatic and feeds on grasses near water. It is up to 24 inches (60 cm) high at the shoulder and weighs as much as 145 pounds (66 kg).

belong in this group, but molecular evidence, as well as skull mechanics, suggests a relationship. Porcupines are historically ground-dwelling creatures, but American porcupines climb and have prehensile tails. All have hairs developed into spines for protection, and these may be barbed. Most South American rodents live on the ground. They include 14 species of cavies, including wild relatives of domestic guinea pigs. Most are compact animals, but one, the mara, is long-legged, speedy, and lives on open plains. Forest-dwelling pacas, agoutis, and acouchis have no tail and slender legs that hold their bodies clear of the ground as they run. Chinchillas and viscachas have fine fur and shelter in burrows, emerging to feed.

Chinchilla (left) The fine fur is an adaptation to life in the mountains.

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Porcupine (above) The African porcupine may run backward in order to jab an enemy with its quills.

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Carnivores

A typical carnivore This creature has the forward-facing eyes that are typical of carnivores.

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N MOST CARNIVORA the canine teeth are long and pointed for killing prey. The lower jaw has little sideways movement, but the jaw muscles have a strong up-and-down bite. The cheek teeth have pointed ridges running back and forward, for slicing meat into chunks before swallowing. The fourth top premolar tooth, and the first bottom molar tooth, work together like a pair of scissors. These “carnassial” teeth are best developed in cats. Hunting requires good senses. The sense of smell is important to many carnivores, and especially well developed in dogs. Hearing can be vital to a carnivore hunting in woodland or tall grass that hides the prey. Sight is important in open country, and is vital to judge the distance before making a final rush or pounce. Carnivores have forward-facing eyes to help them do this. Claws help some carnivores to climb, but they are also weapons to hold prey down, grasp it,

Carnivore means meateater, but among mammals “carnivore” refers to a member of the order Carnivora. This order has 60 million years experience of eating meat.

Built to attack (right) The main feature of this lion skull is the forward-facing jaws that are adapted for attacking its prey.

Concealed weapons (right) A muscle pulling a ligament below the toe is the mechanism by which cat claws are unsheathed.

Relaxed sheath position

Tendon pulls claw down for use

ON THE LAND MAMMALS

or tear at flesh. Their use as weapons is best developed in cats; they have very sharp claws that are retracted into sheaths between brief periods of use. The heaviest carnivores walk on the soles of their feet. So do climbers. The swiftest carnivores, such as dogs and cats, stand on their toes, providing longer legs to increase speed. The first known carnivores were small, weasel-shaped creatures. They soon split into two lines: the ‘‘dog’’ side of the family tree produced the dog, bear, and weasel families; the ‘‘cat’’ side produced cats, civets, and mongooses. On both sides of the family tree, fossils are known of extinct types.

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IT’S A FACT Pangolins are ant-eaters that live in Africa and southern Asia. There are seven species, all covered by overlapping, horny scales. They have no teeth and cannot chew, but have long, sticky tongues to gather insects, and stomachs adapted for grinding them up. The front claws are powerful. Some scientists have suggested pangolins are relatives of South American edentates. Molecular evidence suggests they are closer to carnivores, but split from them long ago. A fossil pangolin 50 million years old is known from Germany.

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Built for speed (right) The skeleton of the wolf shows how well the creature is adapted for fast, long-distance running.

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Ancient carnivores

Megistotherium skull Andrewsarchus and Megistotherium The former (right) was possibly the largest mammal carnivore ever. The latter (left) lived millions of years later in North Africa.

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NE GROUP OF MAMMALS, whose living descendants are hoofed mammals, experimented with meat eating. The group also produced some very large animals, such as Andrewsarchus from about 55 million years ago. The creature was as big as a hippopotamus with a skull 40 inches (1 m) long. The toes ended in hooves, but it had canine teeth and triangular cheek teeth. Andrewsarchus may have been omnivorous, like a bear, or fed on carrion. Creodonts probably came from the same stock as the Carnivora, but were a separate line with no living descendants. They paralleled the carnivores in several ways, even having slicing carnassial teeth in the sides of the jaws, although different teeth were used. They were important 55 to 35 million years ago, but some creodonts lived on for another 30 million years. They carried their bodies low on legs with five-toed feet. Some were small, but others grew to the size of dogs or lions. The biggest may have weighed a ton (tonne). Compared to modern carnivores, their brains were small, their legs short, and they were less agile. From about 35 million years ago Carnivora became the main meat-eaters.

Before the Carnivora, other mammal groups had been the principal meat-eaters.

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ON THE LAND MAMMALS

The earliest Carnivora are called miacids: sixty millionyear-old fossils show small animals with long bodies and tails. They lived in forests, and their legs were short, flexible, and used for climbing. By 30 million years ago many carnivores were living but most of them, like Pseudocynodictis, had long, weasel-like bodies. Later carnivores separated into the families we know today, and others now extinct. Cats produced a number of saber-toothed forms. From 25 to 2 million years ago these were more common than “ordinary” cats. With huge upper canines, these animals needed strengthened jaws and very powerful necks, so they could open their mouths and strike with their sabers. They were adapted to deal with large prey, gripping with the forepaws while stabbing. Some, such as Homotherium, had canines with slicing edges, that could cut through the throat and blood vessels of the victim. Smilodon had conical canines to stab through tough skin.

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IT’S A FACT Smilodon was an American sabertooth that died out about 10,000 years ago. Remains of thousands have been found in tar pits at Rancho la Brea, Los Angeles, California. They probably came to feed on mammoths and bison that were stuck in tar, and ended up being trapped themselves.

© DIAGRAM

In for the kill Smilodon climbs on top of a ground sloth to stab and kill it.

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Modern carnivores

The dog family includes wolves, jackals, and foxes. The larger members of the family, such as wolves and African wild dogs, are running hunters that may pursue their prey for long distances before making a kill.

African hunting dogs These creatures work together to pull down and then kill a zebra.

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OGS CONGREGATE in packs to bring down prey that a single animal could not manage. The smaller members of the family take small prey. Many dogs supplement their diet with vegetable matter. Bears are heavyweights. The largest brown bears in Alaska can reach nearly half a ton (tonne) in weight. The smallest bear, the Malayan sun bear, can weigh 143 pounds (65 kg). All bears walk flatfooted on the soles of their feet, and are not built for running, although Spectacled bear they are faster than humans over a This is one of a rare species short distance. Although capable of which lives in the Andes. killing prey up to deer size, bears also eat fish, berries, roots, honey, and grubs. The raccoon family includes climbers adapted to life in the forests of South and Central America. Many are adaptable omnivores. As well as raccoons there are coatis, and the long-bodied olingos and cacomistles. The red panda lives in Asia and also inhabits trees. The giant

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ON THE LAND MAMMALS

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panda of China, which feeds largely on bamboo, is probably a specialized bear. Weasels range from 8 inches (20 cm) long and 2 ounces (50 g) in weight, to the muscular wolverine at about 33 pounds (15 kg). Most are efficient killers, and some hunt animals larger than themselves. Some, like weasels, hunt on the ground. Others, such as martens, are at home in the trees. This family also includes skunks and badgers. The mongoose family is confined to Asia and Africa: it includes the mongooses, which mainly live on the ground, and the civets, which are climbers. Madagascar has several unusual species of its own, including the fossa, which looks almost like a cat. Hyenas live in Africa and Asia. They have longer front legs than back legs, and very powerful jaws. They can feed on carrion and bones, although some species are accomplished hunters. Cats range worldwide except Australia. Most of the 35 species are nocturnal hunters with excellent sense organs. The black-footed cat of southern Africa is the smallest wild species, whereas the Siberian tiger is the largest wild species.

Kinkajou (above) This creature lives in the trees, and uses its long tongue to consume fruit and flowers.

Striped hyena (above) This creature can be found on land ranging from northern Africa to eastern India.

© DIAGRAM

Stoat (above) This is a ferocious killer which retains its black tail tip, even in its white winter coat.

IT’S A FACT Two carnivores have prehensile tails from which they can hang. The kinkajou, of tropical America, is in the raccoon family. The binturong is a large, hairy southeast Asian member of the mongoose family. Both like eating fruit.

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Primitive hoofed mammals

Brontotherium This creature, 8 feet (2.5 m) tall, with a strange double nose horn, lived in North America over 30 million years ago.

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OME MEDIUM-SIZED MAMMALS started to eat plants, using broad molar teeth to crush them. Their legs became longer and better for running to escape predators. In some, claws became broad, rounded nails. In many, true hooves developed. These animals now stood on tiptoe on specially modified claws. As well as early representatives of modern groups of hoofed mammal, there were other branches that have since become extinct. During much of the last 60 million years—the “Age of Mammals”—Africa and South America have been islands, cut off from the large landmasses to the north. In both evolved types of animal not found elsewhere. Arsinoitherium was an animal that evolved in Africa. Its teeth were obviously for eating plants, and it may have had flexible lips to help it gather food. In this, as in its overall shape, it resembled rhinoceroses. However, its bones show it to be no relation. It had a huge double horn on the nose. It may have been a distant relation of elephants and hyraxes, which were also of African origin. Hyraxes look like short-eared rabbits, but

At present there are many hoofed mammals, such as deer and horses. But varied as modern hoofed animals are, they are only a small part of the range that has existed on the Earth in the last 50 million years.

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ON THE LAND MAMMALS

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IT’S A FACT Another African “hoofed” animal is the present-day aardvark. An ant-eater with a long, sticky tongue and some odd cheek teeth, it grinds its food in the stomach. It lives in a burrow during the day, and comes out to feed at night. There is just a single species, and it seems to be related not to edentate anteaters but distantly to “primitive” hoofed mammals, such as hyraxes. Arsinoitherium (right) This creature was 11 feet (3.3 m) long, and fed on swamp vegetation.

scientists thought that some aspects of their anatomy suggested a relationship with elephants. Recent molecular evidence backs this. Modern hyraxes are 24 inches (60 cm) long or less, but 30 million years ago some were giants that were as big as a small rhino. Uintatherium, from North America, was about 13 feet (3.9 m) long. It belonged to a group of early hoofed mammals known as brontotheres. Some were pig-sized, but many were as big as rhinos. They had skulls with an array of knobbly horns, and often a pair of huge canine teeth in the upper jaw. All have died out.

Hyrax (right) This creature can retract the middle of its sole to form a suction pad to help it to climb trees.

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South American hoofed mammals

Toxodon This heavily-built creature fed on plants in South America until recent times.

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NGULATES, OR HOOFED MAMMALS, have become extinct since North and South America were a single continent about three million years ago. None of them were closely related to ungulates that evolved in other parts of the world. Amazingly, many of them developed characteristics that made them correspond to ungulates elsewhere. So we can see special South American equivalents of horses, elephants, and camels, as well as other types of plant-eater. But they were never exactly the same, so many look very strange to our eyes. One very large group were the notoungulates. Some of these were rabbit-shaped, but some grew much larger than a rabbit, almost to the size of a bear. Another type had a heavy body with three-toed feet, and a rather hippo-like shape. These flourished particularly from about 25 to 5 million years ago. Toxodon survived until recent times, after the land bridge to North America had formed. The pyrotheres were large, heavy-bodied ungulates that lived until about 30 million

While South America was an island, an extraordinary array of hoofed animals, or ungulates, developed there.

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years ago. They had short tusks in their upper and lower jaws, and the nostrils were set back high in the skull. This suggests IT’S A FACT that these animals Thoatherium,as big as a mediumhad a trunk to help sized dog, had a single toe on each gather their food. foot. It also had a more “advanced” Pyrotherium was leg than that of a horse before nearly 13 feet (3.9 m) single-toed horses evolved. long and 6.5 feet (2 m) high, and resembled an elephant. The astrapotheres were another, unrelated group of solidly-built animals with skulls that indicate a trunk or a long, mobile upper lip. The teeth were specialized and undoubtedly evolved for cropping and chopping plant food. The hindquarters seem poorly developed compared to the front legs. Up to 5 feet (1.5 m) tall, these animals lived until almost 5 million years ago. The litopterns were another large group of ungulates. Some of the largest, such as Macrauchenia, were very camellike in shape, but may have had a short trunk to help in feeding. The largest were 5 feet (1.5 m) at the shoulder. Even more interesting perhaps are the horse-like forms, with long legs for running. The side toes disappeared in evolution, just as in the horse, to leave some kinds with just a single hoof for the animal to stand on.

Horse Thoatherium

Macrauchenia This creature looked like a camel, but was not in fact related.

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Odd-toed hoofed mammals

The two major groups of living ungulates are the perissodactyls, or odd-toed hoofed mammals, and the artiodactyls, which are even-toed. Perissodactyls include horses, tapirs, and rhinoceroses.

Malayan tapir This creature is the largest of all the tapirs, and is distinguished from American tapirs by the white patch in the middle of its body.

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N PERISSODACTYLS the main weight is taken on the middle toe of the limb. In evolution the outer toes have disappeared, to three in rhinos and Indricotherium early horses, and to just one in modern This creature was a horses. In the past perissodactyls have giant rhinoceros. been highly successful, but now there are only 16 species. Tapirs are forest animals that feed on leaves and shoots. These are pulled to the mouth by the short trunk of nose and upper lip. Tapirs virtually identical to those of today go back 20 million years, and relatives can be traced back many millions of years. Three species live in South America. One species lives in Southeast Asia. Rhinoceroses evolved from tapirs over 35 million years ago. As well as rhinos like those of today, there were lightly-built “running rhinoceroses,” and some giants. Indricotherium was hornless, had a long neck, and stood 26 feet (7.9 m) high, much taller than a giraffe. It fed on leaves from trees, probably weighed 16 tons (tonnes), and is the biggest known land mammal. Among the five living rhinos, the African black rhino has a prehensile lip and feeds on bushes. The white rhino has a flat muzzle and feeds on grass. There are three Asian species.

ON THE LAND MAMMALS

There are seven species of horse, ass, and zebra in Africa and Asia. Zebras are still abundant, but the others are now rare as wild animals. A series of fossils from the last 55 million years allows us to see the stages of the evolution of the horse. Starting from a forest-dwelling ancestor, feeding on soft vegetation from bushes, and the size of a small dog, horses have gradually become adapted to life on open plains. They have become larger, longer-legged and faster runners. The toes have been cut to a single hoof on each foot. The teeth have become bigger, more complex, and more suited to tough grasses. Ancestors were probably solitary, but most of the horse family now lives in herds, a good way of achieving protection in open country.

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Zebra (above) The stripes are a form of dazzle camouflage.

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IT’S A FACT Rhino horns are made of keratin, the same material as hair and fingernails. This has not stopped them being hunted for their horns for “medicine.” All rhino species are now rare. Indian rhino This creature has a single horn and distinctive skin folds.

White rhino

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Even-toed hoofed mammals

Alticamelus This was a long-necked camel, 10 feet (3 m) tall, that used to inhabit North America.

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N SOME EVEN-TOED HOOFED MAMMALS, only two toes remain, but most artiodactyls also have two small remnant toes high on each foot. These do not normally touch the ground, but in pigs they may do so on soft ground. Early artiodactyls are known from 55 million years ago. In contrast to perissodactyls, there are still many artiodactyls— about 190 species. Most of these are “modern” types, such as deer, antelope, and goats. Artiodactyls have good teeth for eating plants. The more “advanced” families have another way of extracting the most nutrition from their food. They have complex stomachs with several chambers where plants are fermented and broken down. These animals chew the cud. They bring food back from the first part of the stomach into the mouth for a second chewing. Then it goes back down for digestion to continue. They break plant food down more thoroughly than plant-eaters with simple stomachs. There are nine species of the pig family. Most are omnivorous, using their sense of smell and strong snout to dig out roots and grubs, as well as finding food above ground. Many have well-developed tusks which may be used for defense. Most are shy inhabitants of woodland.

Even-toed hoofed mammals, or artiodactyls, include pigs, hippos, camels, giraffes, deer, and cattle. Their weight is supported on two hoofed toes in each foot.

Babirusa This Indonesian pig has tusks that grow through its upper lip. Red river hog This is a large African forest species.

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ON THE LAND MAMMALS

Ruminant stomach The complex stomach of a ruminant, hoofed mammal contains bacteria that help it to digest tough plant food.

Peccaries live in South and Central America. Although superficially like pigs in appearance, they belong to a different family, but share many habits. Many groups of mammal have evolved in one area, spread to other parts of the world, and then declined. They may survive in different places from their origins. Camels appeared in North America 40 million years ago. They evolved into many different types, including Alticamelus, which had a very long neck. The camel family spread to South America only about 2 million years ago. About 10,000 years ago the last camels died out in North America. Today there are two species of camel in Asia, one species in northern Africa, and two wild species of humpless camel—the vicuña and guanaco—in South America.

Vicuña (right) This creature has a fine silky fleece much sought after by hunters.

Bactrian camel (above) This creature lives in the Gobi Desert in central Asia.

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IT’S A FACT Some peccaries live in troops of up to 100. Sometimes a troop member will confront a predator, such as a jaguar, allowing the rest to escape.

© DIAGRAM

Ruminant stomach

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Ruminants

Comparison Syndyoceras, (top) with its strange horns, lived in North America over 5 million years ago. The kudu (right) is a modern African antelope.

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BOUT 16 INCHES (40 cm) tall, chevrotains have round bodies with short, thin legs, ending in four toes, and feed on soft vegetation. They appeared some 40 million years ago, and have scarcely changed since then. Chevrotains offer a good idea of what early ungulates were like. The giraffe family has just two species today. The giraffe, up to 20 feet (6 m) tall, picks leaves from trees and bushes with its long tongue and lips, and lives on the African savanna. The okapi lives in the Congo forests, and has a giraffelike head and tongue, but is a smaller animal with a short neck. It is similar to forms known from fossils in Europe and Asia five million years ago. Even two million years ago Sivatherium, which was heavily built, with branching horns on its face, lived in Africa and Asia. There are nearly 40 species of deer found worldwide except Australia. Most live in forest and woodland where they feed on bushes. They range from the 16-inch-tall (40 cm) pudu of South America to the 7.5-foot-tall (2.3 m) moose of the northern regions. Male deer grow antlers; females do not, apart from reindeers. Antlers are made of bone, and are shed each year. As new antlers grow, they are covered with “velvet,” a furry skin. This is rubbed off when the antler is grown. In most species the antler size increases with increased maturity, acting as a signal of strength. The Bovidae are the biggest artiodactyl family,

Ruminants are artiodactyls that chew the cud. The most primitive of these are chevrotains, of which there are four species living in the tropical forests of Africa and Asia.

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IT’S A FACT Megaloceros lived in the Ice Age, was 3 feet (2.4 m) tall, and had antlers spanning up to 11.5 feet (4 m). Although found across Europe and Asia, it is often called “Irish elk,” as many specimens have been found in peat bogs there. with over 180 species, including cattle, antelopes, wild goats, and sheep. Species live in all habitats, from forests to deserts, from lowland swamps to dry and rocky mountainsides. They did not reach Australia Gaur (above) or South America. Members of this This is the largest of the wild family have a hard gum pad but no cattle of India and Indochina. teeth at the front of the upper jaw. The lower incisor teeth bite against this to crop off vegetation. Many bovids have horns on the head. These true horns have a permanent bony core, with a horn made of keratin on the outside. Both sexes may have Ibex (left) horns, but they are This is a wild goat often much larger that lives on high mountainsides in in the male. Europe and Asia.

© DIAGRAM

Giraffe Food travels from the giraffe’s stomach all the way back to its mouth for a second chewing.

ON THE LAND MAMMALS

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Elephants

There are three living elephant species, two in Africa and the other one in southern Asia. Until fairly recent times the proboscideans were more widespread and numerous. Their fossil history goes back over 50 million years. A number of trends can be seen in their evolution.

Mammoth trapped A drawing by a Stone Age artist shows a mammoth apparently caught in a formidable trap.

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ARLY PROBOSCIDEANS, like Moeritherium, were no larger than a modern tapir. The jaws were long, and filled with low Moeritherium rounded teeth, but there were four This was a small, early small tusks at the front. A series of proboscidean. fossils shows the proboscideans becoming larger, and their legs more pillarlike. The face shortened and instead of all the teeth being in use at once, the massive cheek teeth appear in succession throughout a proboscidean’s life, as its old teeth wear down. The last and largest teeth may appear at 30 years of age. The trunk developed for feeding and drinking. The tusks in many species grew larger, and probably helped in feeding. The first proboscideans evolved in Africa. When Africa ceased to be an island they spread across the world, including the Americas. Apart from elephants, the proboscidean group included the mastodonts, which had less complex teeth. Early specimens were rather similar to Moeritherium. Later types, such as Mastodont itself, looked similar to a true elephant. It lived in North America until a few thousand years ago. Another proboscidean line evolved into animals like Deinotherium, with tusks in the lower jaw only. They curved down and backward.

Gomphoterium This was an early mastodont with tusks in both upper and lower jaws.

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ON THE LAND MAMMALS

African elephant An adult African bull elephant can weigh as much as 6 tons (tonnes).

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IT’S A FACT The woolly mammoth—a close relative of today’s Asian elephant—evolved in the Ice Age and foraged on the cold plains. Ice Age humans saw it and featured it in cave paintings. Specimens are sometimes found frozen in the Russian tundra.

Indian elephant The gestation period of this elephant is 20 months.

© DIAGRAM

They were probably important in feeding, but we do not know how. True elephants reached their pinnacle only about 2 million years ago. There were many species, some closely related to living forms. The biggest, the imperial mammoth, reached a shoulder height of 15 feet (4.6 m), but there were also dwarf elephants on some Mediterranean islands. The African elephant is the largest living species, foraging in forests and on savannas. Its large ears may help it to lose heat. The Asian elephant lives mainly in forests. Despite the large capacity of their guts, elephants digest only part of the food that passes through them. They may feed for up to 18 hours a day, and take in 330 pounds (150 kg) of forage in that time.

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Running birds

After non-bird dinosaurs disappeared, large, flightless, carnivorous birds with enormous beaks evolved. These were distant relations of cranes. In most places their reign was short. Meat-eating mammals evolved and pushed them out. The exception was South America, where, without competition from placental mammal carnivores, hunters such as Phorusthacus became extinct much later.

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ODERN, LARGE, FLIGHTLESS BIRDS include the emu, cassowary, rhea, and ostrich. These birds are known as ratites, which means “like a raft.” This describes their breastbones, which are flat, as they have no need to support large flight muscles. Wings are small or, in cassowaries, practically nonexistent. Feathers are symmetrical, unlike the asymmetric feathers of flying birds. Large, flightless birds parallel hoofed mammals. They have long legs with both the muscle and weight concentrated at the top. To stay as light as possible, the lower part of the leg is largely bone and tendon. Toes are reduced to three in most species. The ostrich is a fast runner on open plains. It has just two toes left on each foot. The larger one ends in a hooflike claw. Today, ostriches are confined to Africa. Rheas live in South America, emus in Australia, and cassowaries in Australia and New Guinea. The smaller kiwis are found only in New Zealand. When humans arrived in New Zealand, there were still large flightless birds, the moas, some of which grew to 11.5 feet (3.5 m) tall. They soon fell prey to hunters, and became extinct. In Madagascar there were flightless species, “elephant birds,” that were at least as tall as an ostrich but more heavily built. They also succumbed to human hunting hundreds of years ago. It seems that, with a few exceptions, flightless birds have evolved and survived on islands with no hunting mammals. Phorusthacus (left) This bird stood 10 feet (3 m) tall, and was a top predator.

ON THE LAND BIRDS

Scientists argue whether the ancestors of the ratite birds ever flew, and whether the different sorts of ratite are related, or are just similar because of their lifestyles. Most believe the evidence shows relationship, and that their ancestors may have flown. Apart from characteristics that go with lack of flight, they all have the bones of their palate arranged in a way different from ordinary birds. They share their old-fashioned palate with tinamous. These South American birds resemble grouse, and can fly, but rather badly. They are thought to belong with the ratites.

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Ratites (above) From left to right, the ostrich, rhea, cassowary, and tinamou show the range of living ratites.

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Emu (left) This bird lives on the plains of Australia.

© DIAGRAM

IT’S A FACT Kiwis have tiny wings and a coat of loose feathers. They are nocturnal, and feed largely on worms. They are unusual among birds in finding food mainly by scent, and having the nostrils at the tip of the beak. They lay the biggest egg, in proportion, of any bird. As in other ratites, the male incubates the egg.

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Tropical rainforest

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N THE TREE BRANCHES in a tropical rainforest grow mosses, ferns, bromeliads, and other plants. If the canopy is not too dense, there may be other layers of trees and shrubs below. Vines climb toward the light, using the shrubs and trees for support. A tangle of lianas hangs down. As well as providing much potential food in the way of leaves, fruits, and seeds, the mass of vegetation provides a huge number of hiding places and types of living space. The tropical rainforest enables more animal species to live in one area than any other habitat on land. Each animal species lives in its own layer of the rainforest. On the floor in the African rainforest are small hoofed animals such as the duiker, and large ones like the bongo, okapi, or elephant. Many animals are solitary creatures with a good camouflage of spots or stripes. They are hunted by leopards, which also climb. In the South American rainforests are an equivalent group of animals, but different species. Tapirs, peccaries, and deer live on the ground, constantly hunted by jaguars. Up in the trees are monkeys, each kind

Tropical rainforest is one of the richest environments on Earth. Plant growth is exceptional in the warm and wet habitat. Trees thrust upward to form a canopy of branches and leaves high in the air, with some taller species standing with their tops above the canopy.

Hylaebraccata Many tree frogs live within the canopy of the tropical rainforest.

Tropical rainforest

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ON THE LAND BIOMES

making use of its own individual section of threedimensional space. Multitudes of insects live on, and inside, the vegetation. Many species of birds eat them, perhaps specializing by hunting on trunks, branches, or leaves, or drilling into bark. Parrots feed on seeds. Toucans in South America, or hornbills in Africa and Asia, pick fruits from the branches. Squirrels clamber along slender branches. Butterflies float above the canopy, while fruit-and insect-eating bats hover in the air. Frogs, millipedes, centipedes, spiders—in fact, representatives of virtually all groups of land-living animals—are abundant in the rainforest. In some ways the tropical rainforest is an easy place to live. However, since so many animals live there, competition exists, which may be why many of them specialize in where they live, and in what they eat.

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IT’S A FACT The tropical rainforests are home to some of the biggest insects in the world. The goliath beetle of Africa grows up to 4 inches (10 cm) long, and reaches 3.5 ounces (100 g) in weight.

Tropical rainforest This contains the most luxuriant vegetation on the Earth. Much of the life is high above ground.

Tall emergent tree

River

Main canopy

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Temperate woodland

Skunk This creature is a small predator in American woodlands.

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ANY OF THE TREES in temperate woodland are deciduous, meaning they drop their leaves in winter. Summer is the season of growth for plants, and most animals produce babies, when most food is available. Although temperate woodland is the normal vegetation for the eastern United States and northern Europe, most of it has been cleared to make way for farmland and towns. Temperate woodland does not have the profusion of species seen in the tropical rainforest, and most of the animals are small. Even here, though, species are surprisingly numerous. There are at least 280 species of insect known to be more or less dependent on oak trees in England. Many larger animals will also use them, plus fungi, lichens, and algae. Oak may be one of the best host trees, but overall the diversity in woodland is high. The trees dominate the forests, but often there is sufficient light for a shrub layer to form, and flowers and rushes grow on the ground. A special feature of the deciduous woods is a springtime bloom of flowers before the leaves of the trees open and shut out light.

In temperate woodlands sufficient rainfall enables trees to grow, but although summers are warm, winter may be cold.

Temperate woodland

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ON THE LAND BIOMES

The small plant-eaters include many insects. Caterpillars chew the leaves. Some tiny caterpillars, and other insects, may spend their whole larval life on one leaf. Seeds, buds, and fruits are food for mammals such as squirrels and mice, and for many birds. The largest plant-eaters in European temperate woodlands are deer and wild boar. Bison are now confined to Poland. Predators should include wolves and brown bear, but over most of the region humans have killed them off. The main predators are now foxes, wildcats, and smaller animals such as stoats and martens. Birds are plentiful and include insect-eaters, such as woodpeckers, and predators, such as the tawny owl.

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IT’S A FACT An important part of the woodland ecosystem is the multitude of organisms that break down dead leaves and twigs that fall to the floor. These include fungi, slugs, and tiny insects, as well as worms. There may be over 2,000 of the latter in the soil under a square yard (meter) of forest. © DIAGRAM

Temperate woodland Traditionally (below), this has diverse flora and fauna, but in many places the natural tree cover has now been replaced by farmland with few species.

Retreating woodland

Farmland on best soils

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Boreal forest

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N MANY PLACES fir and spruce grow densely, shutting out the light from the forest floor beneath. There is little in the way of shrubs or flowers below these stands, but often a thick layer of needle leaves that have dropped from the trees and are rotting slowly. The trees are evergreen, but they still replace their needles gradually. On flat ground there may be spaces in the conifer forest where there are swamps and waterlogged ground. This type of forest is known as taiga. The boreal forest is a very uniform environment. Many of the animals it contains are identical in both North America and Eurasia. It is usually under snow for much of the winter and the season of growth is short. Even more than in temperate forest, many of the birds migrate in for summer and disappear before winter sets in. In the summer the days are long and insects are plentiful. There are small plant-eaters, such as voles and lemmings, woodchucks, and squirrels. Woodchucks hibernate, but most other small mammals stay active in winter, running through

The boreal forest stretches around the Northern Hemisphere in the cold lands north of the temperate woodlands. It consists mainly of conifers, such as fir and spruce.

Moose These animals are found in boreal forest regions of North America and Scandinavia, where they are called elks.

Boreal forest

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ON THE LAND BIOMES

spaces under the snow where they are protected from the worst of the cold. Deer live in the forest— red deer in Eurasia, and the slightly larger wapiti in America. The biggest deer of all, the moose —called elk in Europe—also browses here. Carnivores include sable, martens, wolverines, wolves, and bears. Fewer species live in this habitat than in the temperate forest. As a consequence, food chains may be quite simple. A carnivore, for example, may be heavily dependent on one particular prey. In America, lynxes feed especially on varying hares. These hares get their name from their change to a white coat in winter. They breed fast and, over a few years, their numbers build up to a point where there are too many for the habitat to support—up to 800 per square mile (km). The population crashes to a low, and then builds up again over the next few years. As it is so dependent on the hares, the population of lynxes follows the same cycle, but just slightly behind.

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IT’S A FACT There are also specialist conifer feeders. Crossbills extract seeds from pine cones. Nutcrackers open the cones with their strong bills. Capercaillies, the largest game birds, feed on tough pine needles through the winter.

Crossbill

Boreal forest This is less varied than woodland farther south.

Conifer forest

Water

Swamp

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Tropical grassland

I

N AFRICA, grassland dotted with trees, known as savanna, covers much of the continent south of the Sahara. Although always warm, savanna often has seasons, governed by rain. The grassland is usually dry, but during the short rainy seasons grasses leap into growth and flowers bloom. Insects become more abundant, and birds use the time of abundance to nest. In the dry season, fire may ravage the savanna, but the roots of grasses soon send up shoots again, and dormant seeds spring to life. The grass provides food for a huge number of animals. Large herds of antelope and buffalo graze on the African plains. Each species feeds in subtly different ways, so competition is lessened. Warthogs dig for roots, small gazelles eat short shoots, and zebra feed on longer, coarser grasses. The scattered trees and bushes are also used at various levels, by giraffes, elephants, and browsing antelopes, including the gerenuk, which has a long neck and balances on its hind legs to browse.

Within the tropics, there is some rain, but not enough for to support many trees, so the main vegetation is grass. In South America, Australia, and Africa, there are areas of tropical grassland.

Gerenuk This is an antelope that has specialized in browsing bushes for food.

Tropical grassland



ON THE LAND BIOMES

!

On the hunt The cheetah catches its gazelle prey at speeds up to 60 miles per hour (95 kmph).

Living in herds provides more eyes and ears to watch out for savanna predators. The largest is the lion, but the leopard and the speedy cheetah also hunt here, as well as African hunting dogs and hyenas. Smaller cats, such as the serval, search for small prey. Many smaller savanna animals live in burrows during the day, protected from the hot sun and predators, and emerge to forage at night. Herds of grassland animals move around to find their food. Hundreds of thousands of wildebeest on the Serengeti Plains of East Africa have a definite pattern of migration. They follow the flush of grass growth on the plains after rain, and move to better watered areas during the dry season. They move in long lines, and cross rivers and other obstacles. Calves are born to the wildebeest while the herds are on the move. Tropical grassland Such a habitat, with droughtresistant trees dotted about, can support a large number of grazers and browsers.

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IT’S A FACT Birds, as well as mammals, move about the grasslands to take advantage of conditions. The quelea is a seed-eating finch that is common on African grasslands. After the rains, literally millions can gather to nest in one area, covering thorn bushes with their woven nests— sometimes several hundred in a single tree. Not surprisingly, in some places they are serious pests for farmers.

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Temperate grassland

Outside the tropics, some large areas of grassland exist in temperate regions. They are situated mainly in the drier interiors of continents where there is insufficient rain to sustain trees. These temperate grasslands are known as prairies in North America, pampas in South America, and steppes in eastern Europe and Asia.

J

UST AS TEMPERATE FORESTS are the “poor relations” of tropical rainforests in terms of species diversity, so temperate grasslands have fewer species than the savannas. Nevertheless, the grasslands are still productive enough to hold big herds of grazing animals. Unfortunately for the natural world, some temperate grasslands have been extensively used for agriculture. The prairies of North America were once home to millions of bison but the great herds were hunted almost to extinction, completely changing the prairie ecology even where there is no significant farming. Much smaller wildlife remains. Rodents, from mice and gophers to prairie dogs, feed on the prairie vegetation. Small predators, such as hawks and skunks, eat them. Coyotes are now the top mammal predator over much of the area. In Eurasia, the steppes also support herds of grazers such as the saiga antelope. Formerly there were also herds of wild horses, but these are now very rare. Smaller animals include ground squirrels, known as susliks,

Viscacha This creature lives on the pampas. A colony makes a huge system of burrows with up to 30 entrances.

Temperate grasslands

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ON THE LAND BIOMES

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!

other small rodents, and hares. The winter weather is very cold, and many of the small animals hibernate or stay underground in winter. The saiga antelope move south to escape the cold, and move back again in warmer weather. They are nomadic: always on the move to find better pasture. Wolves live on the steppes, and there are also powerful eagles. Foxes, steppe polecats, and the roundfaced, furry Pallas’ cat are small but effective predators. On the South American pampas there is a lack of big herds of mammals. There are pampas deer, but herds number only five or six. Rheas live on the grassland, and flocks can be up to 30 strong. The rodents include burrowers, such as viscachas and tuco-tucos. The mara is an alert active runner that lives in small groups. Eagles and pampas foxes kill the small plant-eaters for food. The burrowing owl keeps a lookout for small prey from a vantage point on the ground.

© DIAGRAM

Coyote This is a common predator on North American grasslands.

IT’S A FACT Like bison, pronghorn antelope were once common on the prairies. But their numbers have been reduced from 40 million to a few hundred thousand.

Temperate grassland (below) The American prairies are temperate grasslands. Many are now given over to grain farming, but they used to contain huge numbers of bison and other grazing animals.

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Desert

P

LACES WITH LESS THAN 10 inches (25 cm) of rainfall per year are usually classed as desert. The rain may be spread thinly throughout the year, or may all come at once. In some deserts there are years when it does not rain at all. Deserts are usually hot, but some Central Asian deserts are cool, and there are “cold deserts” near the poles with very little rain or snow. Desert plants are specialized to survive. Some trees have roots that go down 100 feet (30 m) to tap underground water. The cactuses of American deserts reduce water loss by having no leaves, and bodies that store water. In other deserts families of plants developed similar adaptations over a period of time. Some types of plant store water in fleshy, underground roots. Yet others survive in deserts by having very fast lives. They grow, flower, and produce seed within days of receiving life-giving rain, then die, but their seeds sprout when it rains again. A limited number of animals can survive in deserts. Some insects have very tough waterproof skins to reduce water loss. Some can make

Deserts occur where there is little or no rain. They may be situated in the middle of continents, like the Gobi Desert of Asia, or where cold currents run along coasts, such as the Atacama Desert of South America.

Sidewinder This rattlesnake moves across sand sideways by throwing its body over and over in loops. Some other desert snakes use the same trick.

Desert



ON THE LAND BIOMES

Dry eroding hill

Rocky landscape with few plants

Shifting sand dunes Desert (above and below) In a desert, rocks and hills are continually eroded. In some places sand forms and wind produces huge, shifting sand dunes.

!

IT’S A FACT Camels cannot avoid the Sun, but achieve some insulation from its rays from their fur, and the fatty humps on their backs. When short of water, a camel may not sweat until its temperature is 140ºF (40ºC), a little above its normal level. It allows its temperature to drop below normal in the cool night, so takes longer to warm up in the morning. It can become much more dehydrated than a human before becoming distressed. When really thirsty, camels can drink more than 60 pints (35 liters) of water. Camels have nostrils which can be closed, long eyelashes, and fur in the ears to keep sand out. They have pads on their toes to stop them sinking in soft sand. Their adaptation for desert life is superb.

© DIAGRAM

use of tiny amounts of dew forming at night. Reptiles also lose water slowly through their dry scaly skins. Even so, they have to hide in rock crevices, or under sand, to avoid the extreme heat which occurs during the middle of the day. Small mammals usually hide from daytime heat and emerge in the cool of the night. Some, like the kangaroo rat, survive without drinking at all. They extract water from the dry seeds they eat, and only produce minute amounts of very concentrated urine.

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Mountains

Mountains have their own climates and provide a unique habitat for a range of wildlife. Climates on a single mountain may vary to a great extent.

Snow leopard This animal hunts high in the mountains of central Asia.

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N MOUNTAINS the temperature drops by about 34°F (1°C) with every 500 feet (150 m) of altitude ascended. Near the summits of high mountains the air is noticeably thinner, which means less oxygen is available than at sea level. The Sun’s radiation may be fierce, but the thin atmosphere does not trap the heat, and the ground may warm up more than the air. Nights are cold, and winds often blow furiously around the mountaintops. Even at the equator, a high mountain like Kilimanjaro may have a permanent snowcap. In between the mountaintop and the plain below is a succession of zones. The zones on a mountain mimic those you might pass through as you moved from equator to pole at sea level. There may be broadleaved

Yak This animal lives higher than any other ox, and has been turned into a valuable domestic animal in Tibet.

Mountains

!

ON THE LAND BIOMES

Himalayas These are the highest mountains on Earth. Mt. Everest is the tallest peak at 29,140 feet (8,882 m).

IT’S A FACT High altitude mammals often have increased oxygen-carrying capacity in the blood. The vicuña has nearly three times as many red blood cells per pint (0.6 l) of blood as humans.

© DIAGRAM

forest at the base, with a band of conifers above. These stop at the “treeline,” where the average monthly temperature is 50°F (10°C). Above this are alpine meadows, changing higher up into vegetation resembling that of Arctic tundra. Above this may be permanent snow. Few animals can live near the mountaintops, but there may be a few insects and mites in sheltered spots. Most insects keep low to the ground when they fly to avoid being carried away by wind. Even so, many insects, seeds, and pieces of plant, are blown up onto the snowfields, where a small number of birds, including choughs, eat them. Most high mountain plants hug the ground. They may have big roots below, but above ground they are flattened or cushionshaped. Hairs may help them to trap heat. Some large mammals survive well on mountains. The yak lives high on the Himalayas, feeding on small plants, such as mosses and lichens in the winter. Its fur is so thick that it can survive subzero temperatures. Various types of wild sheep, goats, and antelope also live on these high mountains, but may move to lower slopes in winter. Marmots stay high in the meadows and rocks, but hibernate during winter. Some species of vole are adapted to the heights. Pikas in Tibet are one of the highest permanent residents, with burrows at 18,045 feet (5,500 m).

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The polar regions

O

N MOUNTAINS Lemmings above the ice These are one of the few some lichens grow. One or two species rodents that are able to survive in the Arctic. of insect and mite have been also been found. But it is really only the fringes of Antarctica that are home to animals—mostly seabirds and mammals that are resting or breeding. Seals haul themselves out of the ice to have their young. Emperor penguins also incubates their eggs and chicks on the sea ice that is stuck to the land. The Arctic, although extremely cold, is more hospitable to life. The central part is ocean, frozen in the winter, but melting at the edges in high summer. Within the Arctic Circle are the northernmost parts of the landmasses of North America and Eurasia. In winter the ground is covered by snow and ice, and for months there is darkness. In summer the days are long and the surface melts, but the subsoil is still frozen. A vegetation of low tundra plants is then exposed. Many are lichens or mosses, but there are also dwarf trees of birch and willow only a few inches (cm) high. Some flowers also bloom in the very brief summer from June to September.

The continent of Antarctica lies in the southern polar region. It is a barren land, permanently covered with ice, with high winds and temperatures that can drop to -126°F (-88°C). Conditions are too extreme for most life forms.

Polar bear This is the top predator in the Arctic, moving over the ice on its furry pads.

Arctic Circle South Pole

North Pole

Sea ice Antarctic Circle

Ice sheet

The Arctic

Antarctica



ON THE LAND BIOMES

Many birds, including waders and geese, nest on the tundra in the light Arctic summer, then migrate once the young are reared. Lemmings are permanent residents in the Arctic, staying under the snow in winter. Ptarmigan, hares, voles, and ground squirrels are other plant-eaters that inhabit this area. Arctic foxes, snowy owls, and hawks prey upon them. The biggest plant-eaters on the tundra are musk oxen, which live in herds for protection. Overall, few species live in the Arctic. Food chains are short, and populations wax and wane over the years, never really reaching a stable equilibrium as they do in more complex ecosystems.

Icebergs In the summer, these break off from the polar ice sheets and drift in the sea. Animals are often carried with them.

!

IT’S A FACT Most small mammals find it difficult to keep warm at low temperatures. However, the Arctic fox, with a head and body measuring 2 feet (60 cm) long, and weighing only 11 pounds (5 kg), has such a dense undercoat that it can sleep on the surface of the snow at -58°F (-50°C) without coming to harm. Its short ears and bushy tail—which it wraps around its face when sleeping—help the fox to conserve a large amount of heat.

© DIAGRAM

Snowy owl (left) The male of this species is almost completely white, The female sits on a nest on the ground and, in contrast, is speckled with black.

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Timeline

Million years ago Events 5,000–4,000 4,550 Formation of the Earth 4,000–2,000 3,600 Origins of life 2,000–400 1,400 First multicellular organisms 700 Ice age 560 First multicellular animals forming communities in the sea 545 Explosion of life in shallow seas; first shelled animals 455 First land plants 445 Ice age Centipede 417 First land animals 400–100 400 Centipedes in existence 375 First spiders; millipedes in existence 360 First “amphibians” 325 First reptiles 300 Ice age; most land forms a single landmass—Pangaea Early “amphibian” 250 Extinction of pelycosaurs 230 First dinosaurs 210 First mammals 205 Beginning of the age of dinosaurs 200 First frogs Pelycosaur 130 Early snakes 100–now 65 Impact of huge meteorite in Gulf of Mexico; extinction of dinosaurs 55 Early primates 50 First shrews 25 Saber-toothed cats come to prominence Early primate 7 First mice 3 Extinction of many South American mammal families 1 Ice age 1 Humans evolve Shrew

ON THE LAND TIMELINE

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Fossils help scientists determine when different kinds of plants and animals first appeared. Era

Millions of years ago

Proterozoic Eon

2,500–543

Proterozoic periods

bacteria, simple animals, and plants exist

Paleozoic

543–490

Cambrian

sea animals without a backbone flourish

490–443

Ordovician

early fish appear

443–417

Silurian

land plants and land arthropods appear

417–354

Devonian

insects and amphibians appear

354–290

Carboniferous

reptiles and flying insects live in forests

290–248

Permian

reptiles dominate

248–206

Triassic

dinosaurs dominate, mammals appear

206–144

Jurassic

birds appear and pterosaurs flourish

144–65

Cretaceous

flowering plants appear

65–1.8

Tertiary

dinosaurs die out, mammals spread

1..8–present

Quaternary

humans dominate

Cenozoic

Main events

© DIAGRAM

Mesozoic

Period

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Glossary

Amber

Amphibian

Caecilian

Coprolite

abdomen The posterior part of the body that contains the intestines in a backboned animal: the rear of three body sections in insects and crustaceans. alpine Living in mountains. amber The fossilized resin of pine trees. amphibian Member of group of animals which may live on land as adults, but lay eggs in water that develop through a larval (tadpole) stage. antennae The feelers on the head of jointed-legged animals. aquatic Living in water. arthropod An animal with an exoskeleton and jointed limbs and body. artiodactyl An animal in the group of hoofed mammals with an even numbers of toes. atmosphere The layer of gases above the surface of a planet or moon, and what we often call the air. biome One of the major regions of the Earth providing particular climatic conditions for plant and animal life—e.g., tropical rainforest, temperate grassland. boreal Northern—particularly used to describe northern coniferous forests. broadleaved Trees that are not conifers. caecilian A type of limbless, wormlike amphibian. canine Doglike; describes the teeth behind the incisors in the jaw, usually enlarged as conical stabbing teeth in meat-eaters. canopy A layer in a forest formed by the interlocking upper branches of trees. carnassial teeth Teeth at the side of a carnivore’s jaw that are adapted to slicing through meat. carnivore An animal that eats meat. carrion The flesh of dead animals, found rather than killed by the animal eating it. cecum The pouch at the start of the large intestine. club moss A type of primitive plant, with small living species, that was often tree-sized 300 million years ago. coprolite Fossilized waste matter. cud Food regurgitated into the mouth from the stomach for a second chewing by a ruminant dehydrated Containing less water than is needed to function properly. diaphragm A muscular membrane between the chest and the abdomen in a mammal. diapsid A skull with two window-like openings at the sides (other than those openings for eyes, ears, and nose). diversity A number of different animals, or habitats, in an area. ecosystem The animals, plants, and other organisms that form an interactive community with their physical surroundings. embryo A developing young animal before birth or hatching. equilibrium A point of balance. erosion The combination of factors—physical and chemical—that break down bedrock until it eventually becomes particles of soil.

ON THE LAND GLOSSARY

Marsupial

Mollusk

Perissodactyl

© DIAGRAM

evolution The process of gradual change by which one type of living thing gives rise to another. fossil The remains or traces of an ancient organism, preserved in rocks by the geological process of fossilization. gastropod A snail or similar mollusk that walks on a muscular “foot,” and has a hard shell over the body. gestation period The period between mating and the birth of a young mammal. Gondwana The large southern landmass that existed hundreds of millions of years ago, which has since separated into the continents of the Southern Hemisphere. herbivore An animal that eats plants. hibernate To go into a resting state for the winter. hypodermic Beneath the skin. A hypodermic syringe injects below the skin. igneous Rocks that have been produced by volcanic processes. incisor teeth The teeth across the front of the mouth in a mammal. insectivore An insect-eater, particularly one of the group of mammals that includes shrews and hedgehogs. isopod A crustacean of the group that includes woodlice, and also many freshwater, deep-sea, and parasitic creatures. Jacobson’s organ A sense organ in the roof of the mouth of vertebrates that can detect chemicals and odors. It is especially well developed in snakes and lizards. keratin The chemical that makes up horn, hooves, claws, and hair. latitude A measure of distance from the equator. mammal A warm-blooded animal that feeds its young on milk. Mammals usually have hair. marsupial One of the group of mammals that gives birth to very immature young, which are then kept in a pouch of skin on the mother for a while. mollusk Invertebrate animal such as a snail or clam, with a soft unsegmented body, usually protected by one or two hard shells. monotreme A member of a mammals’ group that lays eggs rather than having young born alive. multituberculate A member of an extinct group of plant-eating mammals. mummification Preservation of the body by a process of drying. nocturnal Active at night. omnivore An animal that eats both meat and plants. opposable Capable of being placed opposite, like the human thumb to the rest of the fingers. ornithischian A dinosaur belonging to the group with “birdlike” hips. This group were all plant-eaters. palate The roof of the mouth. pampas A grass-covered plain in temperate South America. parasite An animal that lives on, or inside, another and feeds upon it while the host animal is still alive. perissodactyl An animal in the group of hoofed mammals with odd numbers of toes.

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Glossary

Proboscidean

Ratite

Ruminant

placenta A plate of tissue, through which oxygen and other substances can be exchanged, that joins a baby mammal in the womb to its mother. placental A mammal in which the young are nourished inside the mother before birth through a blood-filled organ called the placenta. prairie Extensive grassland, especially temperate grassland in North America. predator An animal that catches and kills other animals for food. primitive An early member of a group of animals, or one showing characteristics believed to be similar to those of early animals. proboscidean An elephant, or relative in the same order of mammals, socalled because most have a long nose (proboscis) that helps in feeding. pterosaur One of the flying reptiles, with a wing of leathery skin, that lived in the time of the dinosaurs. radioactive Elements in which some nuclei spontaneously disintegrate (“decay”), giving off energetic particles. ratite A flightless, running bird, such as an ostrich. resin A thick liquid, becoming solid, that exudes from trees such as pine, particularly where bark is damaged. ruminant An animal with a complex stomach in which the stomach contents are returned to the mouth for a second chewing. saurischian A dinosaur belonging to the group with “lizardlike” hips. This group included plant-eaters and meat-eaters. sauropod A plant-eating dinosaur of the saurischian group that walked on all fours and often grew to great size. savanna A tropical grassland. sediment The particles deposited by wind or water. spinnerets The organs from which spiders produce silk. steppe Dry grassland, particularly on the plains of eastern Europe or Asia. stratum A layer. synapsid A reptile with a single single pair of openings at the sides of the skull. Synapsids are extinct, but gave rise to mammals. temperate Moderate: used to describe parts of the Earth that do not have extreme temperatures. terrestrial Living on land. territorial An animal that defends a particular area for itself or its group against others of its kind. tundra A treeless, cold area with low vegetation in polar regions, or at mountain tops. ungulate A hoofed mammal. venom Poison produced by an animal for killing prey, or for defense. vestige A small relic, or remnant, of an organ that is no longer functional. vocal sac A balloonlike organ in the throat that amplifies sound production in frogs.

Websites to visit

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There is a lot of useful information on the internet. There are also many sites that are fun to use. Remember that you may be able to get information on a particular topic by using a search engine such as Google (http://www.google.com). Some of the sites that are found in this way may be very useful, others not. Below is a selection of websites related to the material covered by this book. Most are illustrated, and they are mainly of the type that provides useful facts. Facts On File, Inc. takes no responsibility for the information contained within these websites. All the sites were accessible as of September 1, 2003. Amphibians Links to many sources on amphibians of all kinds. http://www.herper.com/amphibians.html Australian Wildlife: Marsupials An introduction to marsupials. http://www.australianwildlife.com.au/features/marsupials.htm BBC Education: Evolution: Extinctions An account of mass extinctions throughout the Earth’s history. http://www.bbc.co.uk/education/darwin/exfiles/massintro.htm BBC Walking With Beasts: Fossilization An animated explanation of some fossilization processes. http://www.bbc.co.uk/beasts/fossilfun/makingfossils/ Caecilians Photographs and information about caecilians. http://www.caecilian.org California Turtle & Tortoise Club Links to various sites about tortoises and turtles. http://www.tortoise.org/cttclink.html

© DIAGRAM

GeoZoo: Mammals An excellent index of introductions to groups of living mammals. http://www.geobop.com/Mammals/

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Websites to visit

Open Directory Project: Paleontology A comprehensive listing of internet resources. http://dmoz.org/Science/Earth_Sciences/Paleontology/ Palaeos: Aves Scholarly classification of flightless birds. http://www.palaeos.com/Vertebrates/Units/350Aves/900.html Primates.com Photographs and detailed facts about primates. http://www.primates.com The Talk Origins Archive: Radiometric Dating and the Geological Time Scale A thorough explanation of how rocks—and hence fossils within—are dated. http://www.talkorigins.org/faqs/dating.html UCB, Museum of Paleontology: Biomes Factual website giving information on biomes. http://www.ucmp.berkeley.edu/glossary/gloss5/biome/ UCB, Museum of Paleontology: Introduction to Pareiasauria Some information on pareiasaurs, with links to other primitive reptiles. http://www.ucmp.berkeley.edu/anapsids/pareiasauria.html University of Manchester, Earth Sciences: Mesozoic Arachnids Fascinating photographs of fossil spiders. http://www.earth.man.ac.uk/research/projects/1/site/photos.html University of Michigan, Museum of Zoology: Metatheria Scholarly facts about marsupials. http://animaldiversity.ummz.umich.edu/chordata/mammalia/metatheria.html University of Michigan, Museum of Zoology: Monotremes Scholarly facts about egg-laying mammals. http://animaldiversity.ummz.umich.edu/chordata/mammalia/monotremata.html

Index

B bandicoots 51 bears 72 binturong 73 biomes 6–9 birds 86–87, 95 bison 96 brontotheres 74–75 C camels 81, 99 capybaras 67 Carboniferous period 18 carnivores 68–73 cassowaries 86–87 cat family 68–73 centipedes 24–25 chameleons 41 cheetahs 95 chevrotains 82 chinchilla 67 chipmunks 64–65 climatic zones 8–9 continents 6–7 coyotes 97 crabs 26

creodonts 70 cuscuses 53 D deer 82 deermouse 66 deserts 98–99 dinosaurs 9, 12–13, 34–37 dog family 68–69, 72 duck-billed platypus 47 E earthworms 21 echidna 46–47 edentates 58–59 egg-laying mammals 46–47 “elephant birds” 86 elephants 84–85 elk 93 emus 87 extinctions 12–13 F fleas 27 fossil fuels 18–19 fossils 14–17 frogs 28–29 G gaurs 83 geckos 41 gerenuk 94 gibbons 61 giraffes 82–83 goliath beetles 89 gophers 64–65

gorillas 61 grassland 94–97 guinea pigs 66 H hares 63 hedgehogs 56 hoofed mammals 74–81 horses 79, 96 hyenas 73, 95 hyraxes 74–75 I ibex 83 iguanas 40–41 insects 26, 101 isopods 27 J jack rabbit 62 jerboas 66 K kangaroo rats 99 kangaroos 48–49, 52–53 kinkajou 73 kiwis 86–87 koalas 53 Komodo dragon 40 kowaris 51 kudu 82 L lemurs 60 lions 68 litopterns 77 lizards 40–41

© DIAGRAM

A aardvarks 75 amphibians 10, 29 ankylosaurs 37 anteaters 58 antelope 97 arachnids 22–23 armadillos 58–59 artiodactyls 80–82 astrapotheres 77

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Index

M mammoths 85 marmots 64–65 marsupials 48–53 mastodonts 84 miacids 71 mice 62, 66 millipedes 24–25 moas 86 moles 56–57 mongooses 73 monkeys 60–61 monotremes 47, 54 moose 82, 92–93 mountains 6–7, 100–101 N notoungulates 76 O oil, formation of 19 okapi 82 ornithischians 36–37 ostriches 86–87 P pandas 72 pangolins 69 peccaries 81 pelycosaurs 33 perissodactyls 78 pig family 80 pikas 63, 101

placental mammals 54–55 porcupines 66–67 possums 53 primates 60–61 pterosaurs 12 pyrotheres 76–77 Q queleas 95 R rabbits 62–63 radiometric dating 16–17 ratites 87 red river hogs 80 reptile, early forms of 10, 32–33 rheas 86–87 rhinoceroses 78–79 rodents 62, 64, 66, 96 roundworms 21 ruminants 81–83 S salamanders 30–31 saurischians 35 scorpions 10, 22–23 shrews 56–57 sloths 58–59 snails 21 snakes 42–43, 98 snow leopards 100

solenodons 57 spider monkey 61 spiders 22–23 springhares 65 squirrels 64–65 stoats 73 striped hyena 73 striped tenrec 57 T tamanduas 59 Tamil loris 60 tapirs 78 tarsiers 61 Tasmanian devil and Tasmanian wolf 50–51 temperature belts 8 thylacines 51 toads 28–29 tortoises 38–39 tree frogs 88 tuataras 39 V Virginia opossum 50 W wombats 52 Y yaks 100–101 Z zebra 79, 94