The Dinosaur Book: And Other Wonders of the Prehistoric WorldDK, Smithsonian
Everything you need to know about dinosaurs, pterosaurs, marine reptiles, and mammals in this essential prehistoric encyclopedia for kids.
With more than 1,000 images and fascinating facts, The Dinosaur Book brings young readers face-to-face with some of the most incredible creatures ever to exist. Using a range of full-color images, including spectacular fossilized bones and realistic digital reconstructions, all forms of prehistoric life are covered. Young readers can also find out about the latest scientific discoveries that have changed the way we see these prehistoric animals--from new feathered dinosaurs to how and where.
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BOOK THE DINOSAUR s m i t h s o n i a n BOOK THE DINOSAUR WRITTEN BY JOHN WOODWARD CONSULTANT DARREN NAISH Smithsonian THE SMITHSONIAN Established in 1846, the Smithsonian—the world’s largest museum and research complex—includes 19 museums and galleries and the National Zoological Park. The total number of artifacts, works of art, and specimens in the Smithsonian’s collection is estimated at 154 million. The Smithsonian is a renowned research center, dedicated to public education, national service, and scholarship in the arts, sciences, and history. DK London Senior Editors Shaila Brown, Ben Morgan US Editor Kayla Dugger Senior Art Editor Jacqui Swan Jacket Editor Amelia Collins Jacket Designer Surabhi Wadhwa-Gandhi Jacket Design Development Manager Sophia MTT Picture Researcher Jo Walton Producer, Pre-production Jacqueline Street-Elkayam Senior Producer Alex Bell Managing Editor Lisa Gillespie Managing Art Editor Owen Peyton Jones Publisher Andrew Macintyre Art Director Karen Self Associate Publishing Director Liz Wheeler Design Director Phil Omerod Publishing Director Jonathan Metcalf First American Edition, 2018 Published in the United States by DK Publishing 345 Hudson Street, New York, New York 10014 Copyright © 2018 Dorling Kindersley Limited DK, a Division of Penguin Random House LLC 18 19 20 21 22 10 9 8 7 6 5 4 3 2 1 001–311231–Sep/2018 All rights reserved. Without limiting the rights under the copyright reserved above, no part of this publication may be reproduced, stored in or introduced into a retrieval system, or transmitted, in any form, or by any means (electronic, mechanical, photocopying, recording, or otherwise), without the prior written permission of the copyright owner. Published in Great Britain by Dorling Kindersley Limited A catalog record for this book is available from the Library of Congress. ISBN 978-1-4654-7476-6 Printed in China A WORLD OF IDEAS: SEE ALL THERE IS TO KNOW www.dk.com 20 22 24 26 Before the dinosaurs 28 The first animals Built to survive Set in stone Trilobites The age of fish Fish armor Early life on land Towering trees Arthropod empire Airborne giant Early amphibians Rise of the reptiles Reptiles branch out Hungry hunter 30 32 34 36 38 40 42 44 46 48 50 52 54 56 CONTENTS DK Delhi Senior Editor Anita Kakar Senior Art Editor Stuti Tiwari Bhatia Editors Sneha Sunder Benjamin, Tina Jindal Art Editors Devika Khosla, Debjyoti Mukherjee, Nidhi Rastogi Assistant Editor Aishvarya Misra Assistant Art Editor Ankita Sharma Jacket Designers Suhita Dharamjit, Juhi Sheth Jackets Editorial Coordinator Priyanka Sharma Senior DTP Designer Harish Aggarwal DTP Designers Jaypal Chauhan, Vijay Khandwal, Nityanand Kumar, Rakesh Kumar Managing Jackets Editor Saloni Singh Pre-production Manager Balwant Singh Production Manager Pankaj Sharma Senior Managing Editor Rohan Sinha Managing Art Editor Sudakshina Basu Foreword Timeline of life Changing planet Types of fossils Fossil finds Origin of life Game-changers Evolution and extinction The vertebrates What is a dinosaur? Inside a dinosaur 6 8 10 12 14 16 18 The age of dinosaurs 58 The first dinosaurs Prosauropods Sauropods Mobile necks Titanosaurs Footprints and trackways Stegosaurs About tails Deadly spikes Ankylosaurs Dinosaur defense Iguanodontians Plant-eaters Hadrosaurs Cool crests Dinosaur eggs Dinosaur crèche Pachycephalosaurs Ceratopsians Head-to-head Herds and packs Early theropods Spinosaurids Allosauroids Cutting edge Tyrannosaurs Ultimate hunter Ornithomimosaurs Oviraptorosaurs Arms and hands Protective wings Therizinosaurs Sharp claws Dromaeosaurs Toothed eagle 60 62 64 66 68 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100 102 104 106 107 108 110 112 114 116 118 120 122 124 126 128 Dinosaurs take flight Skin, scales, and feathers Feathered hunters First up Taking off Early birds Giant birds High-speed killer Pterosaurs 138 140 142 144 146 Early pterosaurs Later pterosaurs Prowling predator 148 150 152 Colorful crests 154 The marine world 156 Life in Mesozoic seas Early marine reptiles Flippers and tails Giant marine reptiles 158 160 162 164 Ambush hunter 166 The rise of mammals A new world Trapped in amber The first mammals Giant sloths and armadillos Body cover Mega-marsupials Giant herbivores Horns and antlers Powerful predators Mammal teeth Saber charge Ice-age giants Primates Early humans Window to the past 130 Glossary 132 Index 134 Acknowledgments 136 168 170 172 174 176 178 180 182 184 186 188 190 192 196 197 198 200 204 208 y ce p h a l o s a u G i ga n t s p i n o s a u r u r us s ty ra co sa u r us ch Pa S Foreword The amazing variety of life that exists on our planet is so rich that new kinds of organisms are still being discovered every day. More than 2 million species (types of organisms) have been named and described by scientists, and there are probably millions more waiting to be discovered. But these are only a tiny fraction of the species that have ever existed on Earth in the past. If you were to go back in time 100 million years, you would find yourself surrounded by just as many different animals and plants as today, but—unless you had read this book first—you wouldn’t recognize any of them. Until a little over two centuries ago, no one realized this. They thought that the animals they saw around them had always existed, and that the world hadn’t really changed over time. But in the late 18th century, scientists started examining strange shapes found in rocks and realized that they were fossils— the remains of ancient life that had been turned to stone. Most of these fossils were of seashells and other familiar forms, but some were dramatically different—huge bones, skulls, and teeth of gigantic animals that lived millions of years before the dawn of human history. Using fossils that date right back to the beginning of life on Earth, about 3.8 billion years ago, scientists have been able to piece together most of the history of life. One of the most exciting parts of that story started about 230 million years ago with the earliest dinosaurs. Over the following 164 million years, these animals were to evolve into the most spectacular land animals that have op hy t on Co r y t h o s a u r u s Scia d Phle ge t h o n t i a Je h o l o r n is No th os au r us ever walked the Earth. They included gigantic beasts that weighed as much as 12 elephants; terrifying hunters that could bite their way through solid bone; and strange creatures with horns, frills, and even feathers. The giant dinosaurs were wiped out in a global catastrophe 66 million years ago. But their fossils survive, along with other fossils that show, beyond doubt, that many of their smaller, feathery relatives were able to fly. Some of these feathered dinosaurs survived the disaster to flourish in the new era as birds. So not only do fossils tell us about life in the distant past, they can also reveal astonishing facts about animals that we see all around us every day. Throughout this book, you will find scale boxes that show the sizes of animals compared to either a child, a school bus, or a human hand. Child = 4 ft 9 in (1.45 m) tall School bus = 36 ft (11 m) wide Hand = 6 in (16 cm) long John Woodward T it Wap ti a anis Introduction Timeline of life KEY The story of life on Earth is written in the rocks. Over millions of years, sediments like sand and clay settle on the floors of lakes and oceans and harden to form layer after layer of sedimentary rock. Trapped in these ancient deposits are the fossilized remains of prehistoric organisms, with each layer capturing a snapshot of life from a different period in history. Early Earth Paleozoic Era Mesozoic Era Cenozoic Era Million years ago 251–200 MYA 200–145 MYA Triassic Reptiles ruled the world in the Triassic. They gave rise to the first dinosaurs, the first flying reptiles, and the first true mammals, which were little bigger than shrews. Crocodiles and turtles appeared, and the giant aquatic reptiles cruised the ocean. Jurassic The Jurassic saw the rise of the colossal plant-eating sauropod dinosaurs such as Brachiosaurus, as well as the giant meat-eating theropods that preyed on them. Smaller theropods evolved into the first birds. Deserts shrank and forests of conifer trees, monkey puzzles, and ferns spread across the land. Rhamphorhynchus MYA Allosaurus 299–251 MYA Moschops Edaphosaurus 8 Permian Earth’s climate dried out in the Permian, and deserts replaced forests. Reptiles and related animals called synapsids were the dominant land animals. Unlike amphibians, which breed in water, reptiles laid waterproof eggs and could breed on land. At the end of the Permian, most of Earth’s species were wiped out by a catastrophe of unknown cause. 4.6–0.5 billion years ago 542–488 MYA Precambrian The Precambrian is a supereon that makes up nearly nine-tenths of Earth’s history. For most of it, the only life forms were single-celled organisms in the ocean, such as cyanobacteria. Fossilized imprints of much larger, leaf-shaped organisms that might have been animals appeared about 600 million years ago. Known as the Ediacaran organisms, these life forms vanished at the end of the Precambrian. Cambrian A wide range of new animal fossils appear in rocks from the Cambrian Period. A sudden burst of evolution— the Cambrian explosion—seems to have produced animals with the first limbs, heads, sense organs, shells, and exoskeletons. All the major categories of invertebrate alive today originated in the Cambrian, from mollusks and arthropods to echinoderms such as Helicoplacus (a relative of starfish). Cyanobacteria Helicoplacus Geological periods Earth’s history stretches back 4.6 billion years. This vast span of time is divided into long sections called eras, which are divided in turn into shorter sections called periods. The Jurassic Period, for instance, is when many of the dinosaurs lived. The periods are named after different bands of sedimentary rock, each of which has a distinctive collection of fossils. 23–2 MYA 2 MYA to present Neogene Mammals and birds evolved into recognizably modern forms in the Neogene. Our ape ancestors left the trees and adapted to life in grasslands by walking on two legs. Quaternary Our ancestors evolved larger brains in this period and invented ever more ingenious tools to hunt, make fire, build homes, sew clothes, and farm the land. Dryopithecus Homo habilis 66–23 MYA Uintatherium Chalicotherium Paleogene The death of the giant dinosaurs allowed mammals to take their place. They evolved from small nocturnal creatures into a great diversity of land and sea animals, including giant herbivores such as Chalicotherium, which used its long arms to reach the highest branches of trees. 145–66 MYA Cretaceous Dinosaurs of the Cretaceous included Tyrannosaurus and the plant-eating ceratopsians, which had distinctive horned faces, neck frills, and beaks. All dinosaurs except for a few birds perished in a mass extinction at the end of the period, along with many other prehistoric animals. Sigillaria Meganeura Ichthyornis Magnolia Triceratops 358–299 MYA 416–358 MYA Carboniferous This period gets its name from the carbon deposits found in its rock as coal. Coal is the fossilized remains of lush rainforests that covered the land. These were home to giant millipedes, giant dragonflylike insects, and early amphibians, which had evolved from Devonian fish. Devonian Fish ruled the ocean in the Devonian, which is sometimes called the age of fish. The largest of them were placoderms—jawed fish with armor-plated bodies to protect them from their enemies’ jaws. Rolfosteus 488–444 MYA 444–416 MYA Ordovician Warm waters covered much of Earth in the Ordovician, submerging the continent that would later form North America. The oceans teemed with trilobites—large, pillbug-shaped creatures that scuttled across the seabed or swam shrimplike through the water. The first fish and starfish appeared, and simple plants probably began to colonize the land. Silurian Coral reefs flourished in the Silurian, providing habitats for the first fish with bones and the first fish with powerful, biting jaws rather than sucking mouths. Land plants remained small, but they began to acquire the tough, water-carrying veins that would later form wood and trigger the rise of trees. Trilobite fossils Baragwanathia 9 Introduction Changing planet If you were to travel back in time to the Mesozoic Era—the age of dinosaurs—Earth would seem like an alien world. The continents had different shapes, the climate was hotter, and strange prehistoric plants covered much of the land. Dinosaurs and their prehistoric relatives ruled this world for nearly 200 million years. The vast span of time is divided into three different periods, each with its own distinct animal and plant life: the Triassic, the Jurassic, and the Cretaceous. 251–200 million years ago Horsetail Coelophysis Ginkgo Shonisaurus Moss Triassic world Placerias 10 At the start of the Triassic Period, the continents were joined in a single supercontinent called Pangea. Its interior was desert, but the climate was wetter near the coast, allowing forests of ginkgo trees and giant horsetails to grow. The first dinosaurs—small, two-legged meat-eaters—appeared in the Triassic. They coexisted with stocky, tusked, plant-eating animals such as Placerias—a relative of early mammals. Changing planet 200–145 million years ago 145–66 million years ago Jurassic world The giant continent of Pangea split during the Jurassic, torn apart by volcanic forces from deep inside Earth, and formed two large new continents. Moist sea air could now carry rain to more of the land, allowing forests to replace desert. Dinosaurs became the dominant land animals, and some evolved into giants, such as Barapasaurus, a long-necked plant-eater. The first feathered and flying dinosaurs evolved, including Archaeopteryx, a birdlike predator. Velociraptor Alxasaurus Sequoia Archaeanthus Archaeopteryx Barapasaurus Mosasaurus Cretaceous world Cycad Fern During the Cretaceous, the continents drifted toward their current configuration, moving about as fast as your toenails grow. Flowering plants, which had appeared in the Jurassic, evolved into trees and replaced older vegetation. There were now more kinds of dinosaurs than ever, including Velociraptor, a small carnivore with lethal, hooklike claws on its hind feet, and Alxasaurus, a feathered herbivore. 11 Introduction Types of fossils Most of what we know about prehistoric life comes from fossils— the remains of ancient organisms entombed in rock. The study of fossils and the sedimentary rocks containing them has enabled scientists to piece together a record of life on Earth. Natural cast Fossils can form in various ways. Some of the most common fossils are casts— replicas of a whole body or a body part that formed from minerals building up inside a cavity. This ammonite cast formed when minerals built up inside the animal’s spiral shell after its soft inner tissues decayed. Ammonite cast How fossils form Only a tiny fraction of the animals that lived in the past left fossils behind. Fossils of land animals are especially rare because they form only in unusual circumstances. The animal must die in a place where its body is undisturbed and scavengers can’t easily consume it. Mud or sand needs to cover the remains, which must stay buried for millions of years as they slowly turn to rock. Geological forces must then bring the fossil back to the surface, where it can be found. 12 The body of a drowned Tyrannosaurus sinks to the muddy floor of a delta, where a river meets the sea. Thousands of years later, layers of mud and sand have buried the skeleton. The flesh slowly rots away, leaving behind hard body parts such as bones and teeth. Dinosaur drowns Flesh decays Sediment builds up Trace fossil Fish fossil Fossils that record an organism’s activity—such as footprints, burrows, nests, or droppings—are known as trace fossils. Fossil footprints help us understand how animals moved. Archosaur footprint Mold Mineralization Most fossils involve a process called mineralization. Water seeping through the sediment dissolves remains such as bone and deposits crystallized rock minerals in their place, slowly turning the bones to rock. Types of fossils This cast fossil replicates a trilobite’s shape. Mold fossils form in the same way as casts, but they preserve an imprint of the body rather than a replica of its shape. Trilobites were common sea creatures that grew by shedding their outer skeletons, leaving millions of fossils behind. Trilobite mold Amber This mold fossil preserves an impression of a trilobite’s body. A few fossils preserve the whole body of a prehistoric animal. Amber is a transparent yellow material formed from fossilized tree resin. It sometimes contains tiny animals that became trapped in the sticky resin as it oozed from a tree. Petrified tree Petrification Whole tree trunks can be fossilized by a process called petrification, which preserves minute details. First, groundwater seeping through buried wood deposits crystals of silica inside tiny spaces. Then, more slowly, minerals gradually replace the wood fibers, turning the trunk to stone. Prehistoric fly in amber Millions of years later, the continents have moved and the dinosaur fossil is no longer under the sea. Glaciers or other processes erode the ground, wearing away the sedimentary rock. Erosion finally reveals the fossil, allowing paleontologists to excavate it. Water seeping through the layers replaces the bones with rock minerals, turning the fossil to rock. Bones turn to rock Continents move Erosion of surface Discovery 13 Introduction BURGESS SHALE Country: Canada Famous fossil: Trilobites This 508 million-year-old layer of shale rock in the Canadian Rockies has some of the world’s oldest animal fossils. SOLNHOFEN Country: Germany Famous fossil: Archaeopteryx Limestone from this quarry contains some of the most perfect Jurassic fossils found, including Archaeopteryx, a feathered, birdlike dinosaur. DINOSAUR NATIONAL MONUMENT Country: US Famous fossil: Allosaurus At least 11 dinosaur species have been found here, entombed in rock that formed on a riverbed. GHOST RANCH Country: US Famous fossil: Coelophysis More than 1,000 skeletons of the small Triassic dinosaur Coelophysis make this site one of the world’s largest dinosaur bone beds. AUCA MAHUEVO Country: Argentina Famous fossil: Saltasaurus Once a floodplain beside a river, this desert is littered with broken dinosaur eggs from the Cretaceous— probably the remains of a nesting colony of the sauropod Saltasaurus. HELL CREEK Country: US Famous fossil: Triceratops Many dinosaur fossils have been found in this site, which was once a forest bordering an ocean that submerged the American prairies. VALLEY OF THE MOON Country: Argentina Famous fossil: Eoraptor Some of the earliest dinosaurs known to science were found in this desert valley, which resembles the lunar surface. Fossil f inds 14 Most fossils are found in sedimentary rock that formed from ancient layers of mud and sand. Sedimentary rock is found worldwide, but a few key sites have especially clear fossils of animals that didn’t fully decay, preserving fine details like feathers or skin. Many fossils are found in deserts, not because animals fossilize well in deserts, but because the large expanses of exposed rock make fossils easier to spot. MESSEL PIT Country: Germany Famous fossil: Darwinius The rock in this quarry has preserved incredibly detailed fossils of animals that were poisoned by volcanic gases and then sank into a lake. LIAONING Country: China Famous fossil: Sinosauropteryx The dinosaur fossils of Liaoning are beautifully preserved after being buried under layers of volcanic ash in the late Cretaceous. These fossils show that many dinosaurs had feathers rather than scaly skin like reptiles. Fossil f inds GOBI DESERT Country: Mongolia Famous fossil: Velociraptor In the late Cretaceous, the Gobi Desert had conifer forests, lakes, streams, and many dinosaurs, including the meat-eater Velociraptor. EDIACARA HILLS Country: Australia Famous fossil: Dickinsonia Mysterious leaf-shaped imprints found in Australia’s desert may be the remains of soft-bodied sea animals that lived 600 million years ago. BAHARIYA OASIS Country: Egypt Famous fossil: Spinosaurus A desert oasis now, this site was once a coastal marsh inhabited by fish-eating Spinosaurus—the largest predatory dinosaur known. KEY Cenozoic TENDAGURU Country: Tanzania Famous fossil: Kentrosaurus The spiky-tailed stegosaur Kentrosaurus was found in Jurassic sandstone hills at this site in East Africa. Cretaceous Jurassic MOUNT KIRKPATRICK Country: Antarctica Famous fossil: Cryolophosaurus Most of Antarctica is buried under ice, but this rocky outcrop allowed five Jurassic dinosaurs to be found. Triassic Cambrian Precambrian 15 Introduction Origin of life Life on Earth began at least 3.5 billion years ago, and possibly more than 4 billion years ago. These oldest-known life forms were microscopic single cells that lived in water—tiny capsules of watery fluid containing the complex chemicals vital to all types of life. How these cells formed is still not known, but the process was probably fueled by the heat and chemical energy of hot springs, either on land or on the deep ocean floor. Early Earth Planet Earth was formed from the rock and dust that orbited the newly formed Sun. As the planet grew in size, its gravity attracted more rocks and comets, which contained water and the chemical elements needed for life. All the rocks impacting the growing planet made it heat up until it melted. Later, the planet cooled enough for liquid water to settle on the surface. Even today, liquid water is vital to all forms of life. The early Earth’s surface was bombarded by giant lumps of space rock. 16 The impacts generated intense heat—for much of its early life, the planet was a ball of molten rock. First life Origin of life The first living organisms must have formed in water containing simple chemicals dissolved from rocks. Today, this type of chemical-rich water erupts from hot springs on the ocean floor and in places like Yellowstone National Park. The water contains microscopic organisms that resemble some of the earliest living things, so it is likely that life began in such places. It is this microbial life that gives Grand Prismatic Spring its vibrant colors. Grand Prismatic Spring, Yellowstone National Park The hot spring is fringed with microbial life. Tiny, tough-walled bubbles were the first living cells. First cells Living cells Life involves chemical reactions that occur in microscopic, tough-walled containers called cells. The earliest living cells were simple bags of fluid, like modern bacteria. They soaked up energy and used it to turn simple chemicals into complex substances vital to life, such as proteins. This helped them grow, multiply, and form large colonies like the ones that live around hot springs today. Evidence of early life The oldest-known rocks on Earth contain microscopic structures that have been identified as fossil Archaea— organisms similar to bacteria. The rocks, which formed on the ocean floor, are at least 3.8 billion years old. But much clearer evidence of early life exists in the form of fossil stromatolites. Dating from about 3.4 billion years ago, these were once colonies of microbes called cyanobacteria that built up in dome-shaped layers. These layers are clearly visible in the fossils. Stromatolite fossil 17 GAME-CHANGERS The shallow waters of Shark Bay in Western Australia support a life form that has existed on Earth for billions of years—stromatolites. These muddy-looking lumps have been built up by cyanobacteria—simple microbes that turn air and water into sugar using sunlight. This process of photosynthesis creates most of the food that animals need and releases the oxygen they breathe. When cyanobacteria evolved in the oceans more than 2.5 billion years ago, there was very little oxygen in the air. Over millions of years, they pumped out so much that it now makes up more than a fifth of the atmosphere. This was vital for the evolution of animals, which need oxygen to turn food into energy. So all the animals that have ever lived owe their existence to these microbes. Free-living cyanobacteria are still widespread in oceans and on land, but thriving stromatolites are rare because they were ideal food for some of the animals that evolved in the world they had created. The ones in Shark Bay survive because few animals can live in the very salty water of its lagoons. Introduction Evolution and extinction Fossils reveal how life has changed over time. This was not fully understood until the 19th century, when fossils became important evidence supporting the theory of evolution by natural selection. Developed primarily by English scientist Charles Darwin, this theory showed that the individuals in a species vary in their ability to cope with the hardships of life— some survive and breed, while others do not. As a result, species gradually change over time as they adapt to the changing world. New species evolve, and older ones may die out completely, becoming extinct. Fossil evidence When the first fossil of Archaeopteryx showing wing feathers was discovered in 1861, it was seen as powerful evidence in favor of the theory that living things evolve over time. Bony tail ❯ At first sight, this 150-million-year-old fossil of an Archaeopteryx looks very like a living bird, with broad, feathered wings. But it had a long, bony tail like an extinct dinosaur. This combination of features does not exist in any modern animal. Natural selection Every animal is different from its parents. This natural variation produces individuals with different strengths and weaknesses, so some are more likely to survive. An insect with more effective camouflage than its cousins will be more likely to evade hungry birds, breed, and pass on its advantages to its young, Meanwhile, its less well camouflaged relatives may die out. 20 The jagged edges and pattern of lines add to the leaf insect’s superb camouflage. Leaf insect Archaeopteryx New species If birds fly to a new habitat, such as an oceanic island, they may face difficulties in finding food. Those that survive will be the ones that, by some stroke of luck, have features that help them cope with the new conditions. If they manage to breed, their young will tend to inherit these features. Over many generations, this may give rise to an island form that is clearly different from its mainland ancestors. This process creates new species. The ancestor had a thick beak for cracking seeds. This finch uses its hooked beak to slice through fruit and buds. A probing beak is ideal for pulling seeds from flowers. A beak with an overbite is perfect for digging up grubs. A pointed beak helps this finch to peck insects off leaves. A tool-holding beak enables this finch to use a twig to dig out prey from bark. Evolution and extinction Wing feathers ❯ The fossils of Archaeopteryx preserve traces of feathers that are very similar to those of modern birds. But the fossils also show that it had the teeth and bones of a theropod dinosaur. Galápagos finches The Galápagos Islands in the Pacific Ocean are home to several species of finch, each with a beak specialized for a different type of food. It is clear that they all evolved from the same ancestor, which probably arrived from nearby South America. Lost ancestors The processes of evolution and extinction cause a relentless turnover of species, with new ones evolving as others die out. This means that, over the past 500 million years, more than 90 percent of all species on Earth have vanished. We only know about these life forms because their remains have survived as fossils. Trilobites don’t exist today—they flourished in ancient seas about 500 years ago. Archaeopteryx fossil Mass extinctions Sometimes a catastrophic event changes the world so radically that very few animals can survive it. This is called a mass extinction. Since life began, there have been five major mass extinctions. Each one wiped out much of the life on Earth at the time, allowing new species to evolve and take over. Trilobite fossil ORDOVICIAN (440 MYA) Up to 60 percent of marine species perished in a mass extinction at the end of the Ordovician Period. DEVONIAN (358 MYA) The Late Devonian extinction mainly affected oceanic life, especially in shallow coastal seas. 60% TRIASSIC (200 MYA) Many of the animals that coexisted with early dinosaurs died out at the end of the Triassic Period. 70% PERMIAN (250 MYA) The Permian Period ended with a global catastrophe that almost wiped out all life on Earth. 75% 96% CRETACEOUS (66 MYA) This mass extinction destroyed the pterosaurs, giant dinosaurs, and most of the marine reptiles. 75% 21 Introduction The vertebrates Vertebrae ❯ Vertebrates get their name from a chain of bones called vertebrae that form the neck, backbone, and tail. Shoulder blade Until about 530 million years ago, all animals were invertebrates— creatures with no internal jointed skeletons. But then new types of animals appeared in the oceans, with bodies strengthened by a springy rod—the beginnings of a backbone. These evolved into fish—the first true vertebrates and the ancestors of amphibians, mammals, reptiles, and birds. Vertebrate evolution FISH JAWLESS FISH BONY FISH SHARKS AND RAYS TETRAPODS AMPHIBIANS MAMMALS REPTILES TURTLES AND TORTOISES Vertebrates make up just 3 percent of animal species, but they include all the large animals we are most familiar with. The first vertebrates were fish. Some fish evolved leglike fins and became the first four-legged land animals (tetrapods). These evolved into the amphibians, mammals, and reptiles. The reptiles known as archosaurs gave rise to the pterosaurs, dinosaurs, and birds. ARCHOSAURS LIZARDS AND SNAKES MARINE REPTILES CROCODYLIANS DINOSAURS AND BIRDS 22 PTEROSAURS Spines jutting from the top of the vertebrae provided anchor points for the back muscles. Upper hip bone Framework ❯ The backbone between the shoulders and hips supported this plant-eater’s head, neck, and tail, as well as the ribs. The backbone was made up of interlocking bones that were light but strong. All large land animals are vertebrates, because a heavy land animal needs a sturdy internal skeleton to support its weight. During the age of giant dinosaurs, strong bones enabled land animals like Diplodocus to grow to colossal size. The only animals that weigh more are whales, but their weight is supported by the water. The vertebrates Diplodocus Leg bones ❯ The immense weight of this giant dinosaur was supported by massive leg bones, linked to the backbone by strong, mobile joints. Reptile Archosaur Fish Mammal Types of vertebrate We usually think of the vertebrates as fish, amphibians, reptiles, birds, and mammals. But the birds can also be seen as the most successful and diverse living group of archosaurs, a branch of the reptiles that also included their closest relatives—the extinct dinosaurs. Amphibian 23 Introduction What is a dinosaur? Dinosaurs were a diverse and successful group of reptiles that dominated life on land for about 140 million years. Humans, for comparison, have existed for less than 1 million years. Ranging in size from animals no bigger than pigeons to lumbering giants the size of trucks, they were reptiles, but very different from modern reptiles. Dinosaurs can be split into two groups: lizard-hipped dinosaurs (saurischians) and bird-hipped dinosaurs (ornithischians). These can be split further, as shown. Ancestral dinosaurs Eoraptor The first dinosaurs were small, agile animals that ran on two legs—they would have looked like this Marasuchus, an early, dinosaurlike archosaur. During the late Triassic Period, early dinosaurs evolved in different ways. Most became specialized for eating plants, but some were to become dedicated hunters. Marasuchus 24 Saurischians Saurischian (“lizard hipped”) refers to the typical saurischians that had hip bones like those of lizards. This group included the sauropodomorph plant-eaters. It may also have included the meat-eating theropods, but some scientists think that theropods are more closely related to ornithischians. Ornithischians This group is made up of beaked plant-eaters with relatively short necks. The name means “bird hipped,” because their hip bones resembled those of birds (even though birds were small saurischians and so not closely related). Hypsilophodon Giraffatitan Sauropodomorphs The sauropodomorphs are named after the sauropods—giant, long-necked plant-eaters that did not have beaks and walked on four legs. Ceratopsians Most ceratopsians had horned heads and big, bony frills extending from the back of their skulls. They were plant-eaters with hooked, parrotlike beaks. Alioramus Einiosaurus Pachycephalosaurs These dinosaurs had very thick skulls. They walked on two legs and probably ate a variety of plant and animal food. Theropods Theropods were nearly all meat-eaters that walked on two legs. Some were huge, powerful hunters, but the theropods also include birds. Pachycephalosaurus Marginocephalians Ornithopods The ornithopods were a group of beaked plant-eaters that mostly walked on two feet, but the biggest ones supported some of their weight on their hands. Stegosaurs Stegosaurus Thyreophorans These beaked, plant-eating dinosaurs had rows of tall plates and spikes extending down their backs and tails. They all walked on four legs. Iguanodon Ankylosaurs Sometimes called tank dinosaurs, these plant-eating heavyweights had thick body armor for defense against large theropod predators. Ankylosaurus 25 Introduction Inside a dinosaur Although soft tissues of animals’ bodies seldom fossilize, we can still figure out what dinosaurs were like on the inside. Dinosaurs were vertebrates, and all vertebrates share the same basic body plan, with powerful muscles connected to a jointed skeleton and internal organs that included a heart, lungs, stomach, intestines, and brain. Dinosaurs were once thought to be cold-blooded, lumbering reptiles, but we now think that many were as quick-witted and active as birds, and some may even have been warm-blooded. Backbone Tail muscle T yr ann Leg muscles ❯ Big dinosaurs like this Tyrannosaurus had huge muscles. Heat generated inside the dinosaur’s body kept the muscles warm for maximum efficiency. o sa u r us Thigh muscle Dinosaur features The brain of a dinosaur like Citipati was adapted for sharp senses, not intelligence. 26 Brain The brains of extinct dinosaurs were relatively small, and some were tiny. Most would not have been as intelligent as modern birds. The closest living relatives of extinct dinosaurs have four-chambered hearts. Heart Pumping blood around the body of a giant dinosaur required a powerful four-chambered heart—similar to a human heart, but a lot bigger. Air sacs (blue) stored air and pumped it back through the lungs (red). Lungs Fossil evidence shows that dinosaurs had lungs like those of modern birds, which are more efficient than the lungs of mammals. Inside a dinosaur Hip bone Skeleton ❯ The dinosaur’s weight was supported by a strong skeleton, but many bones had air-filled cavities that reduced their weight. Lung Air sac Lower jaw Arms Heart Stomach ❯ The stomach of a predator like Tyrannosaurus was adapted for holding a lot of meat swallowed quickly after a successful hunt. Fast mover Intestine ❯ Because meat is easy to digest, a meat-eating dinosaur’s intestine was quite short. Plant-eaters had longer intestines to process fibrous food. Hunters like this Tyrannosaurus were built to kill. Big muscles, warm blood, and super-efficient lungs would have given them the speed and strength they needed to pursue, attack, and kill their prey. But smaller plant-eaters also had to be agile and quick on their feet to stand any chance of escaping. Claw The eyes of some predators may have been adapted for night vision, like a cat’s. Vision Their skull anatomy shows that many extinct dinosaurs had sharp senses. Predators like Tyrannosaurus would have had excellent vision, which may have been as acute as a modern eagle’s. The pillarlike legs helped support the weight. Stance Like birds—but unlike modern reptiles—dinosaurs stood with their legs directly beneath their bodies. This helped to support their weight. Scales were made of tough keratin, like human fingernails. Scales The skins of most big dinosaurs were protected by scales. Many small, feathered dinosaurs also had scales on parts of their bodies. Fluffy feathers like this one were for insulation rather than flight. Feathers Many small theropods and even some big ones were covered in feathers. These kept them warm and allowed some of them to fly. 27 BEFORE THE DINOSAURS ar ni r id iu m Pte in a Ch Before the dinosaurs The f irst animals Found in North Carolina, this fossil of a wormlike animal has no evidence of a mouth, eyes, or even a gut. Fossils show that Charnia’s body was made of rows of branches, giving it a striped appearance. The flowerlike fossils of Mawsonites may be the remains of free-swimming jellyfish. w so nite s M a Attached to the seabed by a stalk, Charnia had a leaf-shaped body that absorbed food from the water. 30 Scientists once thought that the first animals evolved about 542 million years ago at the start of the Cambrian Period. The huge span of Earth history before this, known as the Precambrian Period, was thought to be almost lifeless apart from bacteria and similar microscopic single-celled organisms. But in 1957, a fossil was discovered in the Precambrian rocks of Charnwood Forest in England. It was a multicelled life form, now known as Charnia. Scientists then realized that fossils of similar organisms found in the Tr in a Tribrachidium resembled a sea anemone and had a circular body that was made up of three similar parts. The body was divided into many segments, but it had no obvious legs. The first animals chidium Sp g r ig ibra The head may have had eyes and a mouth. The first known Precambrian fossil, Charnia, was found by a 15-yearold schoolboy. The largest known fossils of Dickinsonia are more than 4 ft (1.3 m) long and show a distinctive body with a central groove, but no one knows if it even had a head. Dick ins o ni a Ediacara Hills of Australia in 1946 were also Precambrian, and more than 600 million years old. These were some of the first animals on Earth. Since then, similar fossils have been found in North America, Africa, and Russia. Many, including Charnia, were animals that lived rooted on the seabed, like modern corals. Others, like Spriggina, were free-living animals that could roam or swim in search of food, and some, including Dickinsonia, were so unlike any modern animal that their nature and way of life are still a mystery. 31 Built to survive ma Ano locar Mar rella The body was divided into segments with long flaps on each side. is plac lico This pear-shaped sea creature had spiral grooves around its shell. He Anomalocaris reached a length of 61 ⁄2 ft (2 m)—the size of an adult human. us Marrella was a tiny, shrimplike creature. These spiked claws were used to grasp prey. 32 The earliest animals that lived in ancient oceans had soft bodies, like modern jellyfish. But during the Cambrian Period, from 542 million years ago, new types of animals appeared. They had hard shells, spines, and tough external skeletons, such as those of Anomalocaris and Marrella. These hard parts supported their bodies and helped protect them from enemies. When the animals died, their soft parts were eaten or rotted, but their shells and skeletons were often preserved as fossils. The appearance of many fossils in These long, sharp spines were probably used for defense. Ottoia’s thorny mouthparts were used to seize small prey and even members of its own species. Built to survive a a toi axi Wiw Ot Waptia The long antennae may have detected food in the water. Armor plates ia Echmatocrinus had up to nine plated tentacles attached to the top of its body. Ha l l u c i ge n Seven pairs of stiff spines protected the long, wormlike body. bi ni a Op a Eyes The flexible legs were like those of a modern velvet worm. This trunklike feature was used for catching prey. Echmatocrinus rocks of this age shows that a wide variety of new animals appeared at the same time. This is known as the Cambrian explosion. Soft-bodied animals like the burrowing worm Ottoia thrived too, and are preserved in rocks such as Canada’s Burgess Shale. Creatures like Ottoia and the shrimplike Waptia are similar to modern animals, but others, including Opabinia, were so odd that we are still not sure how they functioned. 33 SET IN STONE High in the Rocky Mountains of British Columbia, Canada, lies one of the most incredible fossil sites—the Burgess Shale. It was discovered in 1909 by American fossil hunter and scientist Charles Walcott, who realized he had stumbled upon a treasure trove of ancient life. He was to spend much of the next 14 years working on the site, splitting the rock to reveal over 65,000 fossils. More than 500 million years ago, the Burgess Shale was a muddy seabed at the foot of a coastal cliff. The water teemed with animals, some of which were buried by mudslides. As the mud turned to rock, their remains were preserved as flattened fossils, recording the variety of life that had evolved by the start of the Paleozoic Era, about 444 million years ago. Some of the fossils were of animals that had exoskeletons, such as these trilobites, but many more were of soft-bodied animals that were very different from the creatures we see today, such as the five-eyed Opabinia. These animals provide scientists with a spectacular snapshot of life millions of years ago. Trilobites Paradoxides was one of the earliest and biggest trilobites, growing to 15 in (37 cm) long. Phacops had a pair of compound eyes, each made up of many small lenses. Parado x ides The armored body curled up into a ball to protect its soft underside from attack. D t ro op d C u r l e ps o Phac s Ceratalges The long spines would have made this a prickly mouthful for a predator. 36 Trilobites, with their segmented bodies, are among the most distinctive fossils found in ancient rocks. The earliest trilobites appear in rocks that are more than 520 million years old. They thrived in the oceans for an amazing 270 million years until the catastrophic mass extinction that ended the Paleozoic Era 252 million years ago. Trilobites were some of the earliest arthropods—animals with external skeletons and jointed legs, like today’s insects and spiders. Many trilobites like Drotops looked like flattened pillbugs, with several pairs of legs Un cu r le d Ph ac s Trilobites op Walliserops The body of Phacops was made up of 11 segments, each bearing a pair of legs. The three-pronged spear may have been used to fight rivals. Sel enopeltis Ditomopyge Og ygop The dome-shaped, bumpy head shield covered the trilobite’s mouthparts. si s Like many trilobites, this was probably a seabed hunter and scavenger. These fossils may be the empty skins of Selenopeltis—all trilobites shed their skins as they grew. Xystridura This was one of the most common trilobites found in Burgess Shale, Canada. Ogygopsis Paradoxides and large eyes; trilobites were among the first animals to evolve compound eyes packed full of lenses, just like those of today’s insects. Some, including Ceratalges and Walliserops, had spectacular spines that may have been for courtship or defense. Many would have foraged The tail was made up of many segments fused into a single plate. for food on the seabed, but others could swim. There were at least 17,000 known species, ranging from tiny creatures less than 1 ⁄8 in (3 mm) long to animals that were as big as this book. 37 The long spine projecting from the head may have been venomous for defense. With its elongated body, this late Paleozoic shark looked more like an eel. Ch e ro i Before the dinosaurs The age of f ish le pi s Xena The backbone extended into the upper lobe of the tail, as in modern sharks. This bony fish had a sharklike tail. th ca n S t e t h a ca n t h us us The body was covered in tiny, diamond-shaped scales. As A long, flexible “whip” trailed from each side fin. tra sp is The fins of this spiny shark were supported by stout spines. Ch ei ra ca nt hu The head of this primitive jawless fish was protected by scaly armour. s 38 All land vertebrates, including dinosaurs, are descended from fish—the first animals to have backbones. Fish evolved from soft-bodied creatures like Pikaia, which lived over 500 million years ago. Early forms like Astraspis had a soft, jawless mouth and a flexible rod called a notochord in place of a bony spine. Over the next 100 million years, fish developed hinged jaws and backbones. During the Devonian Period, 416–358 million years ago, they became so successful that this period is known as the age of fish. Two main groups Unlike modern sharks, the mouth was at the tip of the snout rather than on the underside. C l a do e se l a c h k Pi a A long, flat body extended from behind Pikaia’s small head. Stethacanthus had many The age of f ish The strange flat-topped structure on the back of males may have been used to attract a female. ai Pikaia was a primitive chordate—an animal with a spinal cord but no bones. tooth-like scales on its head and dorsal fin. This armored fish had a bony head shield. Co c The shark’s sleek, streamlined body was adapted for fast movement through the water. H ol op t yc co s s fos u e t s il Large scales covered the body of this lobe-finned fish. hius The paired fins under the body contained strong limb bones. evolved—sharks like Stethacanthus and Cladoselache had skeletons made of a rubbery material called cartilage, while the so-called bony fish like Cheirolepis had skeletons of hardened bone. Some of these fish also had four stout, bony fins beneath their bodies. Called the lobe-finned fish, they were the first vertebrates to crawl out of the water and live on land. Fish have continued to flourish ever since; even though the largest mass extinction wiped out 90 percent of marine species 251 million years ago, fish managed to survive. 39 Before the dinosaurs Fish armor The broad head was covered in small bony plates, forming a strong suit of armor. e Dr pa n p as The back of this early jawless fish was protected by bony scales. is Bi r n ke ia Drepanaspis had a fin only on its tail. The mouth pointed upward. Most of the body was not armored, allowing flexibility for swimming. Rolfosteus was only about 12 in (30 cm) long. The head shield extended into a long tubelike snout that may have been used to uncover prey hiding in the seabed. Rol fo s eu t s Ce ph ala spi s Dunkleosteus could grow to a colossal 20 ft (6 m) long—as big as a great white shark. The mouth was underneath its broad head shield, suggesting that Cephalaspis fed on the seabed. 40 Many early fish had tough armor protecting their heads, and sometimes their bodies too. The first of these armored fish appeared more than 400 million years ago. The jawless Cephalaspis and Drepanaspis had big horseshoe-shaped head shields. They were much smaller than the armored, jawed fish that evolved later—the placoderms. Some of these massive jawed fish were monstrous looking. Their heads and upper bodies were covered with tough, overlapping plates of bone that were hinged to allow movement. The armor A massive shield of bone protected the head and back of this giant predator. D u n k l e o s te u A serrated rodlike structure extended from the mouth of this armored, jawless fish. s Do r ya spis Athe Tough bony plates completely enclosed the head. B Dipterus had bony plates protecting its head and gills. ri oth ole p Sharp, bony plates in the fish’s mouth acted like a beak and were probably just as effective as teeth. naeg is is The winglike pectoral fins of Bothriolepis were also armored like its head. The structure of the tail was similar to that of a shark. Dipterus may have provided defense against predators. The only animals that might threaten them were sharks and other big, fish-eating predators, since the fearsome marine reptiles with their powerful jaws did not appear in the oceans for another 100 million years. Some of the placoderms, like Bony scales covered most of its body. the great white shark–sized Dunkleosteus, would have had few enemies—it had one of the most powerful bites of any fish and bony plates that were about 2 in (5 cm) thick. It is also likely that they were armored as defense against each other. 41 Early life on land This fossil preserves a leaf frond of one of the first woody trees, which lived about 370 million years ago. Ar The cup-shaped structures held the male and female cells needed to form new plants. s ter i op ae il c h fo s s Sciadophyton was about 2 in (5 cm) tall. The small, scalelike leaves soaked up sunlight and used it to turn air and water into sugar. S c i a d o p hy t o n Aste r ox y lon Veins carrying water through the stem allowed Asteroxylon to grow up to 20 in (50 cm) high. 42 Until about 500 million years ago, there was no life on land. The continents were barren rock and sand like the surface of Mars. The first land organisms were probably microscopic bacteria that built up in mats. These were followed by fungi that lived off the bacterial mats and broke them down to form soil, allowing early plants to get a root-hold. Spores of these plants have been found in fossils that formed about 476 million years ago. The plants would have looked like Aglaophyton and Sciadophyton— simple, mosslike plants that grew close to the Elkinsia These egg-shaped capsules produced spores that could grow into new plants if they fell on damp ground. Elkinsia was one of the first plants to produce seeds instead of spores, which allowed it to grow in drier places. Found near hot springs about 396 million years ago, Aglaophyton had green stems instead of leaves. Ag All la o p Early life on land Seeds were held within these structures. hy t o n early air-breathing animals were small, insectlike creatures. These veins carried water and sap through the plant. ch us Pa l o ae in ar Growing to 26 ft (8 m) high, Prototaxites would have dominated the landscape 415 million years ago. Palaeocharinus had eight jointed legs and a pair of long sensory palps, like most modern spiders. ground in damp places. Over time, plants evolved veins that allowed water and sap to flow through stems connecting their roots and leaves. This allowed them to grow taller, eventually leading to trees like the 20-ft- (6-m-) high Archaeopteris— the first tree to have dense wood and true leaves Prototaxites and to form large forests. Meanwhile, the fungi, bacteria, and plants provided food for early land animals like the millipede Pneumodesmus. These small animals were in turn hunted by predators, including the spiderlike Palaeocharinus. 43 s This fossilized leaflet had a heart-shaped base. nd ron This early conifer had a tall, straight trunk and short, needle-shaped leaves. Le pid od e Macroneuropter i Before the dinosaurs Towering trees The bark of this giant clubmoss had a distinctive diamond pattern. Despite its fernlike leaves, Alethopteris produced seeds instead of spores. W a lc hi 44 Lepidodendron Alethopt er i s a Alethopteris Although known as the age of fish, the Devonian Period also saw the transformation of land habitats by plant life. The first woody trees appeared in the late Devonian, about 385 million years ago, and spread to form the earliest forests. During the next 85 million years, throughout the Carboniferous Period, trees and other plants colonized the land and created habitats for animal life. Many of these plants grew in swamps, and when they died, their remains formed peat that ultimately turned to coal. Some trees, such P Pa r i p t e r i s se ar ipte r i s leaf ed Ferns like Paripteris were some of the first plants to evolve seeds. Shed leaves left scars that formed a honeycomblike pattern on the bark. This primitive plant resembled a tree fern. Glossopteris once formed lush forests Wat tieza Glossopteris means “tongue fern,” describing its leaf shape. Sigillar ia on the continent of Antarctica. The fossilized leaves were very like modern fern fronds. Ne u rop ter is pter ve a s so le Glo is as Sigillaria and Lepidodendron, looked similar to modern trees but were clubmosses—relatives of mosses and ferns. These could grow to great heights— Lepidodendron towered 130 ft (40 m) or more. Many plants resembled modern s spore-bearing ferns and horsetails, but others, including Alethopteris and Paripteris, bore true seeds. By the late Carboniferous, plants like Walchia had evolved—the first of the pinelike conifer trees that later became an important food source for dinosaurs. 45 Arthropod empire The complex compound eyes with many lenses were just like those of modern adult insects. Rock formed from fine-grained mud has preserved the wings of this early dragonfly. Tupus fossil Cy Meganeura may have had a colorful tail. p clo The first flying insects took to the air at least 250 million years before the first birds. h t h a l mu s f o s s il Each wing was a thin plate of plasticlike chitin, stiffened by struts called veins. 46 Forests of towering trees and other plants spread over the land from about 358–299 million years ago, providing food for many small plant-eating animals. They included soft-bodied animals like worms, whose burrows have been found fossilized. But most of M eg aneu ra The jointed legs of an extinct type of scorpion are clearly visible in this fossil found in central Europe. the fossilized land animals of this period were arthropods—creatures with tough external skeletons and jointed legs, like today’s insects, spiders and crustaceans. They included early millipedes like Euphoberia, and plant-eating insects like Archimylacris—a type of Millipedes like Euphoberia were some of the first animals to live entirely on dry land. This 310-millionyear-old insect used its piercing mouthparts to suck plant sap. Like all early flying insects, Stenodictya flew on two pairs of wings like those of dragonflies. en o di ct ya il Ga The long, slender pincers of this scorpion are very like those of the more venomous modern scorpions. llio Living 300 million years ago, this cockroach would have fed on decaying plant material on the forest floor. A Euph ss a fo i r e b o rc m hi Arthropod empire St yl a c r i s f o s s il fos sil A beautifully preserved fossil reveals dark bands on the wings of Lithomantis. The long tail was probably tipped with a powerful stinger for defense and killing prey. cockroach. They were hunted by predatory centipedes, early spiders, scorpions like Cyclophthalmus, and insects like Meganeura. The forests would have been buzzing with these animals, especially insects that, in an era before birds, were the only animals able to fly. Many Lithomantis fossil would have spent most of their lives as wingless nymphs or grubs that lived underwater or in the ground, before emerging as winged adults. Like modern mayflies, these may have had very short adult lives, but they have survived for millions of years as fossils. 47 AIRBORNE GIANT Some of the most spectacular insects that ever lived flew through the lush forests of the Carboniferous Period, about 300 million years ago. They were griffinflies—extinct relatives of modern dragonflies, but far bigger. Fossils of the largest known dragonfly relative, Meganeura, show that its wingspan reached more than 27 in (69 cm), almost four times the size of the biggest living dragonflies. Like its modern counterparts, Meganeura was a hunter that preyed on other insects. It probably used the same predatory technique, targeting airborne prey and seizing them with its bristly legs. Flying back to a perch, Meganeura would then use its powerful biting jaws to chew through its prey’s tough armor to reach the soft flesh within. Meganeura would have laid its eggs in water, and after these hatched, the young would live underwater for several years before emerging to change into adult flying insects. The puzzle about Meganeura is how it could grow so much bigger than any living dragonfly. One theory is that higher oxygen levels in the atmosphere allowed insects to grow larger than they do now. Early amphibians The webbed feet were used mainly as paddles for swimming. Acanthost e Cra s s ig y r in This animal belonged to a group of amphibians that had snakelike bodies. ga Pa n d The skin may have been camouflaged for protection from predators. er icht hy s us E r yo p s The tiny limbs were probably only used for swimming. Although a fish, Panderichthys could probably breathe air. All modern land vertebrates— including us—are descended from these animals. Stout skeleton was adapted for life on dry land. 50 The first four-legged animals on land were amphibians, much like our modern frogs and salamanders. Their ancestors were Devonian fish like Panderichthys and Eusthenopteron, which had unusually stout bones supporting the four fins beneath their bodies. Some of these fish, the immediate ancestors of tetrapods, evolved to survive out of the water by using their lungs and mouths for breathing. Acanthostega and Tiktaalik may have lived at least partly on land. By about 358 million years ago, amphibians T aa ik t lik The strong bony fins were to evolve into legs. Se Early amphibians P h l e ge t h o n t i a y m o u r i a fos s i l Seymouria’s skull was unusually thick and strong. Powerful tail propelled this fish through water. Eustheno Amphiba mu pteron The body was protected by big scales. s Long front and hind limbs were the same size. such as Amphibamus had developed proper feet, but they still had to keep their skin moist to survive. They also had to return to the water to lay their eggs, because the eggs of all amphibians are like those of fish, and dry up if they are not laid in wet places. Eventually, amphibians similar to Eryops and Seymouria evolved into a group of animals that were better adapted to live on dry land— the first reptiles. 51 u Before the dinosaurs ru au Sc a tos Tough, bony plates helped protect this plant-eater from predators. s ur u so s Proterogyrinus Me Rise of the reptiles s This aquatic animal lived like an amphibian but had developed reptilelike eggs. The broad, strong skull was probably adapted for burrowing. Westlothiana is named after Stout, pillarlike legs supported the animal high off the ground. ho in Scotland, where its fossils were found. n West Lothian P r o co l op The slender body and short legs may have been an adaptation for burrowing. Scales stopped vital body moisture escaping easily through the skin. 52 Early amphibians could live on land, but they lost body moisture through their thin skin and had to lay their eggs in water or damp places if they were to survive. During the Carboniferous Period, some amphibianlike animals resembling Proterogyrinus and Westlothiana evolved eggs enclosed in shells that retained moisture, so they could be laid in dry places. They also developed thicker skin covered with tough, waterproof scales that stopped the body losing moisture. They were the ancestors of the first true reptiles—animals such o Spin aequalis Rise of the reptiles Spinoaequalis lived in water but was only partly aquatic—it returned to dry land to breed. The feet were well suited to life on land. Hy pe ap r od e do n The piglike, plant-eating Hyperodapedon had a razor-sharp beak. Like modern crocodiles, Mesosaurus hunted in the water. tloth Wes iana S l ono g a t e pi s Related to the ancestors of dinosaurs, this armored Triassic reptile ate a wide variety of food. as Spinoaequalis and Mesosaurus, which would ultimately give rise to lizards, snakes, and crocodiles. This new type of vertebrate was ideally equipped to colonize dry land during the Permian Period—an age of huge deserts that began 299 million years ago. Permian reptiles included a variety of plant-eaters like the armored Scutosaurus as well as sharp-toothed hunters. Some survived the catastrophic mass extinction at the end of the Permian and became the ancestors of the dinosaurs. 53 Ef f a Va no ps This synapsid had a barrel-shaped body. Mo igi ra Before the dinosaurs Reptiles branch out sc h op The sail was probably used for display, but may have also helped it to absorb or lose heat. s The long limbs enabled this hunter to chase after small prey. Pla r ce ia s Dimetrodon had daggerlike canine teeth at the front for tearing into flesh, and numerous sharp-edged teeth at the back. Dim e t r o do n The two big tusklike canine teeth were probably used for digging. Ophiac o do n The semiaquatic Ophiacodon could use its powerful limbs as paddles. 54 Long before the first dinosaurs, about 320 million years ago, some reptiles evolved into animals known as synapsids— they would eventually give rise to the mammals. The earliest of these animals— Ophiacodon and Varanops—had sprawling lizardlike limbs. Some, including the predatory Dimetrodon and plant-eating Edaphosaurus, had huge “sails” on their backs supported by rodlike spine bones. Later, about 299 million years ago, these reptilelike animals gave rise to a group of animals called dicynodonts—Placerias Archosaurs like Postosuchus had a huge head. Postosuchus The armor of small, bony plates protected its back. preyed on early dinosaurs. Slender and agile, Effigia ran on two legs like a bird. us The crocodilelike powerful jaws were packed with sharp teeth. s Po t u os ch Ed a pho sa u r u s The jaws of this plant-eating animal were lined with numerous blunt teeth. was among the largest of these animals. A few similar animals survived the catastrophic mass extinction at the end of the Permian and evolved into cynodonts, which became the ancestors of modern mammals. Meanwhile, the reptile line had given rise to archosaurs—the group of animals that eventually included crocodylians, pterosaurs, dinosaurs, and birds. Some of the more powerful Triassic archosaurs, like Postosuchus, were the top predators of their time. Others, including Effigia, were very similar to the first dinosaurs. 55 HUNGRY HUNTER Concealed by its camouflaged scaly skin, which closely matches the surrounding ferns, a hungry, sail-backed Arizonasaurus stalks a herd of plant-eating dicynodonts—relatives of mammals. Reptiles like Arizonasaurus were the main threat to plant-eaters in the mid-Triassic Period, before the evolution of big predatory dinosaurs. The first dinosaurs evolved during the Triassic Period, but they were not the giant, ruling reptiles that we are familiar with. The Triassic world was ruled by reptiles of a different type—animals like Arizonasaurus. They were archosaurs, as were the dinosaurs, but had evolved along different lines to resemble high-walking crocodiles. Many had massive jaws and teeth and were capable of overpowering and eating any animal they might encounter. Arizonasaurus belonged to a group of archosaurs that had tall “sails” on their backs, supported by bones extending up from the spine. The function of the sail is uncertain, but it may have been important during displays to rival animals of the same species. THE AGE OF DINOSAURS r Eo The age of dinosaurs The f irst dinosaurs Eoraptor had two different types of teeth, indicating that it ate both small animals and plants. H r er r e ap to r a sa u r u s The long, narrow skull had a jaw full of big, serrated teeth adapted for eating meat. Each hand had five fingers, but only three of the fingers had claws. N ya s a s a u r u s Incomplete fossil remains make it hard to know if Nyasasaurus was a true dinosaur. 60 Although dinosaurs evolved into some of the biggest and most spectacular land animals the world has seen, they had small beginnings. About 240 million years ago, in the early Triassic, the largest reptiles were powerful, crocodilelike archosaurs. These had some smaller archosaur relatives with slender bodies and long legs, such as Marasuchus, which was just 28 in (70 cm) long and chased after small prey on its hind legs. The bigger, slightly more dinosaurlike Silesaurus had a similar build, but seems to have eaten plants, This close relative of the first dinosaurs had a very slim, lightweight body. M ar as uc h us Siles aur us Relatively short arms show that this animal ran on its back legs, like early dinosaurs. The long front limbs were used for walking, but Silesaurus was probably able to rear up on its hind legs. Eoraptor’s fossils are some of the oldest known dinosaur remains. e co d o n Th t AGILE ARCHOSAURS o sa ur us Thecodontosaurus was about 6 1 ⁄2 ft (2 m) long and had a bulky body. Early dinosaurs and their close relatives were all archosaurs, sharing features that make them hard to tell apart. They all had long legs held beneath the body, an agile build, and gaps in their skulls filled with air. Gap in front of the eye socket was an archosaur feature. Dinosaurs had hip joints similar to ours. One of the lower leg bones of a dinosaur was very thin. as well as small animals. These light, agile creatures were closely related to animals like Nyasasaurus, which may have been one of the first true dinosaurs. The first definite dinosaurs— animals like Eoraptor—lived about 230 million years ago and were probably omnivores that ate The hands were used to gather food. a variety of foods. They soon gave rise to specialized predators like Herrerasaurus, as well as plant-eaters like Thecodontosaurus. These animals were the ancestors of the giant dinosaurs that were to dominate life on land for the next 140 million years. 61 Prosauropods Fossils of this giant prosauropod were found in La Rioja Province, Argentina. Set within its jaws were small, leaf-shaped teeth that had serrated edges to help slice through vegetation. s u ur R j io as a M a sp s so o n d yl u s The long, flexible neck was well adapted for browsing on tree foliage. The strong back legs supported all of the dinosaur’s weight, leaving its hands free. Seitaad The remains of Seitaad, meaning “sand monster” in the Navajo language, were found near the Grand Canyon. 62 Soon after the evolution of the first dinosaurs in the middle Triassic (around 230–225 million years ago), dinosaurs began to diversify into species with different lifestyles. Some specialized in eating plants. They evolved long necks that helped A heavy tail balanced the dinosaur’s body at the hips, enabling it to reach up into the trees easily. them reach into trees, but their heads stayed relatively small. One of the earliest, Saturnalia, was only about 6 ft (1.8 m) long, but its relatives were to get a lot bigger; by the late Triassic, Riojasaurus was about 33 ft (10 m) long and weighed as much as an elephant. These Anchi sa u At just 6 1⁄2 ft (2 m) long, this slender, lightweight dinosaur was one of the smaller prosauropods. r us Saturnalia Prosauropods The skin may have been patterned for camouflage in the dappled shade of Triassic forests. a Pl t s eo r au Riojasaurus Found in China, this horse-sized prosauropod was a close relative of Plateosaurus. us Strong hands could grip branches to pull them within reach of the dinosaur’s jaws. L u fe n go sa ur u s Fossils of Plateosaurus have been found in more than 50 places in Europe. S at u r n a l i a Light and agile, Saturnalia would have run through the forest like a large wild turkey. dinosaurs were the ancestors of the enormous sauropods, so they are known as prosauropods. They stood on two legs, balanced by their long tails, and used their shorter arms to gather food. Plateosaurus had grasping hands with four fingers and a powerful clawed thumb, which may also have been useful for defense. When it closed its jaws, its upper teeth overlapped the lower ones like scissor blades to slice through leaves. The tough, fibrous plant material was processed in a big digestive system to extract as much food value as possible. 63 Sa ur op os ei d Sauropods on Ca m a r a s a ur us This giraffelike dinosaur carried its small head high for feeding in the treetops. Many well-preserved Camarasaurus fossils have been discovered in North America. The forelimb bones were very strong, helping to support the body’s considerable weight. The huge stomach could hold a lot of leaves. This dinosaur had unusually big thigh muscles that would have given it a powerful kick, possibly for defense. Apa t o sa ur u s Ba ra pa sa ur us Barapasaurus was about 59 ft (18 m) long and roamed the open woodlands of India. The hand bones were arranged vertically to form a weight-bearing column. 64 With their bus-sized bodies and elongated necks and tails, sauropods were the biggest dinosaurs ever to roam the Earth. These giants were plant-eaters; they would have browsed continually to fuel their enormous bodies. The earliest ones appeared about 200 million years ago and were similar to Barapasaurus. Unlike their prosauropod ancestors, they used their arms to support their bodies, and their hands became weight-bearing feet. Despite this, many could probably rear up on their hind legs to feed in the treetops. Others, Brontomerus was a macronarian—a type of sauropod with a very big nose compared to its skull. Hundreds of teeth lined the front of the distinctive shovel-shaped snout. Gi o sa u r u s Sauropods phor ff n S no sa u r u s ita Am pi ra ge r at The immensely long neck spines were probably for display to rivals and breeding partners. Ni a r ga sa u r u s Nigersaurus usually held its neck high but could lower it to feed on small plants. Giraffatitan was twice as tall as a modern giraffe. This sauropod had a spiked club at the end of its tail, possibly for defense or fights with rivals. The forelimbs of Giraffatitan were unusually long, giving it a very high reach. Apatosaurus had a very long, almost whiplike tail. The massive feet had to support a lot of body weight, equivalent to four elephants. like Sauroposeidon and Giraffatitan, had long arms that helped raise their shoulders much higher than their hips, allowing them to reach the tallest trees without rearing up. The simple teeth of typical sauropods were adapted for biting or ripping leaves from trees, but not for chewing. Amargasaurus Sauroposeidon They swallowed the leaves and relied on their huge digestive systems to process them. A few sauropods like Nigersaurus had more complex teeth at the front of their wide snouts. These teeth may have been specialized for eating plants growing at ground level. 65 The age of dinosaurs Mobile necks D i p l o do c us Diplodocus had 15 neck bones—some were 3 ft (1 m) long. Mamenchisaurus had 19 neck bones— the most of any known dinosaur. Co e l o p hy ru s Mam e n c h i sa ur us E i n i o sa u sis The neck was just long enough to graze on low-growing plants. Some dinosaurs—especially the plant-eating sauropods—had such astonishingly long necks that it is hard to imagine how they held their heads up. The neck of Mamenchisaurus could be up to 59 ft (18 m) long, which is eight times This dinosaur had a long, flexible neck. longer than the neck of a full-grown giraffe. Dinosaur neck bones, or vertebrae, were full of air cavities that made them light, enabling the animals to strip leaves from tall trees. Small, nimble The neck bones of Amargasaurus had bony spines that may have formed a spiky crest. Am T yrann g ar o sa u r u s as r au us Although Tyrannosaurus had a short neck, it had powerful neck muscles that helped support the enormous head. Sauropods had the longest necks of any known animal. S t e go s aur us The underside of the neck was protected by plates of bone hidden in the skin. predators such as Coelophysis had S-shaped necks that they could straighten in an instant to snap up small prey. Big hunters like Tyrannosaurus had stout, massively powerful necks to support their huge skulls and jaws and to give them the strength to tear prey apart. But most ornithischians, including Stegosaurus and Einiosaurus, had relatively short necks suitable for feeding on low-growing plants. The age of dinosaurs Titanosaurs The very long neck of Patagotitan enabled it either to gather leaves from treetops or reach down to feed near the ground. Dr The teeth were probably spoon-shaped and quite small, suitable for biting through leaf stems. ea d n o ug h t u s About 98 ft (30 m) long, Dreadnoughtus was another gigantic animal with a big appetite. Its name means “fears nothing.” us lt a sa ur The body of this small, short-necked titanosaur was armored with bony plates, each up to 5 in (12 cm) across. Sa 68 Until quite recently, scientists thought that the giant sauropods had mostly died out by the end of the Jurassic Period, 145 million years ago. But since the 1980s, many sauropod fossils have been discovered showing that they lived on and continued evolving until the very end of the age of dinosaurs. These late sauropods are known as titanosaurs. The name is misleading, because it suggests that they were all titanic giants. They were certainly big, and some of them were colossal—Patagotitan, for example, could turn Pa t a g o t i t a n COLOSSAL GIANT Found in 2008 in Patagonia, Argentina, the bones of Patagotitan are so big that its total length is estimated to be up to 121 ft (37 m), with a weight equivalent to 12 African elephants. Only the blue whale is heavier. Titanosaurs had long tails, but not as long as the tails of many earlier sauropods. This is one of the few titanosaurs that has been preserved with a fossil skull, so we know that it had a short snout. M a l a w i sa u r u s out to be the biggest land animal that ever lived. But other titanosaurs, including Saltasaurus and Malawisaurus, were no bigger than elephants, which is small by sauropod standards. Over the 80 million years of their existence, the titanosaurs evolved many different head shapes Despite this animal’s immense weight, it walked on the tips of its hand bones. and body forms, suited to a wide variety of feeding habits and lifestyles. Despite this, they were all herbivores, specialized for devouring vast quantities of leaves and other plant material. Fossil evidence also suggests that they probably lived in herds and nested together. 69 GLOBAL RANGE The skin was probably covered with small scales and occasional bigger ones. Titanosaurs were first discovered in South America but have since been found in Europe, India, Mongolia, China, Africa, and even Antarctica—showing that they were a global success story. Pa t a g otitan The bony osteoderms embedded in the skin of this animal’s back seem to have been a common feature of many titanosaurs, and some were much more heavily armored. Am pe a los ur u s Most of the weight of Patagotitan was supported by its back feet, which were cushioned with wedge-shaped pads like those of elephants. 70 In many ways, titanosaurs were typical sauropods, with long necks, long tails, and bulky bodies supported on all four limbs. In giants like Patagotitan and Puertasaurus, their length, bulk, and especially weight were close to the maximum possible for a land animal. But they had other, more distinctive features. Their hands were better adapted for bearing weight than those of earlier sauropods, and later titanosaurs like Saltasaurus and Nemegtosaurus had no finger bones; they stood on pillarlike structures made up of the Patagotitan Saltasaurus Pu The neck of this giant titanosaur was up to 30 ft (9 m) long, and its total length may have been anything up to 98 ft (30 m). Ne m eg t os au ru er t a sa ur u s Titanosaurs With its long neck, Puertasaurus could reach food more than 49 ft (15 m) high. s The skull of this dinosaur has never been found, so scientists have had to base this reconstruction on the fossil remains of close relatives. Known from a single skull found in the Gobi Desert of Mongolia, this titanosaur is 70 million years old, making it one of the last giant dinosaurs to walk the Earth. same bones that form the palms of our hands. Titanosaurs had unusually broad chests, and this meant that their forelimbs were spaced wide apart; trackways of fossilized titanosaur footprints are easy to recognize because the marks left by their feet are so widely spaced. Many titanosaurs also had a feature not seen in earlier sauropods—body armor. The skin of Ampelosaurus, for example, was studded with tough, bony plates and spikes called osteoderms, which would have helped protect it from the teeth of big predators. 71 The age of dinosaurs Footprints and trackways Front and back feet made differentsized footprints. 72 Iguanodon Found in Mongolia, giant footprints up to 61⁄2 ft (2 m) wide were made by titanosaurs. Ankylosaurus Fossilized bones can tell us a lot about how the dinosaurs were built, but less about how they lived. Fossilized footprints, however, can show how dinosaurs walked and ran and whether they lived alone or in a group. A single footprint does not tell us much more than what type of animal made it; the most interesting information comes from trackways— sets of footprints left by animals on the move. The angle and spacing of the prints show how they placed their feet. The spacing also reveals the stride length, and if this varies, it indicates Walking L R L L L R Stride length 83⁄4 ft (2.7 m) Stride length 181⁄2 ft (5.7 m) Titanosaur Apatosaurus Coelophysis a change of speed. Small and large footprints found together might have been left by a family, while a complex pattern of overlapping footprints could be evidence of a whole herd on the move. One 113-million-year-old trackway in Texas can even be read like a Three-toed footprints are typical of theropod hunters. Footprints and trackways If we know how long a dinosaur’s legs were, the length of its stride indicated by a line of footprints can show how fast it was moving. It may also show it speeding up or slowing down. Running STRIDE LENGTH Acrocanthosaurus story, since it seems to show a big sauropod being stalked by a hunter—possibly the powerful theropod Acrocanthosaurus. At one point, the footprints converge, perhaps revealing the exact spot where the predator made its attack. 73 ntr D a ce A medium-sized dinosaur, Loricatosaurus lived in Jurassic England and France. us The age of dinosaurs Stegosaurs Lo r i ca t a os ur ur us The flat, diamond-shaped plates were covered with a tough layer of skin. Ch ia lin go sa At 13 ft (4 m) long, Huayangosaurus was one of the smallest stegosaurs. ur u s This dinosaur from China is one of the oldest species of stegosaur. Hu ay an go sa u r us The front legs were shorter than the back legs, so the head was close to the ground. 74 With a double row of tall, pointed, bony plates running down its back and tail, Stegosaurus is one of the most instantly recognizable dinosaurs. But it was just one of many similar stegosaurs that lived during the Jurassic and early Cretaceous Periods in various parts of the world—the US, Europe, India, China, and southern Africa. All stegosaurs were covered with plates and spikes along their backs, and many, such as the extra-spiky Dacentrurus and Kentrosaurus, also had spikes sprouting from their shoulders. These may have been used Found in Jurassic Europe, Dacentrurus reached lengths of up to 26 ft (8 m). The shoulder spines of Gigantspinosaurus were as long as its front legs. Chialingosaurus At 30 ft (9 m) long, Stegosaurus was the biggest of the plated dinosaurs. Stegosaurus nt spin Giga osaur u s This dinosaur was covered with both plates and spikes. n Ke t ro S t eg s o sa u r u The tail was tipped with four sharp spikes that were about 3 ft (90 cm) long. sa ur u s Tuojiangosaurus had tall, triangular plates along its back. The back legs were much longer than the front legs. The long back legs supported the dinosaur’s weight. T u o j i a n go r sau us The feet had strong, blunt hooves. for defense, while the spikes on the end of a stegosaur’s tail would certainly have been used to lash out at a predator. But the spectacular plates may have been brightly colored to attract a mate. All stegosaurs were plant-eaters, with narrow, beaked mouths that were ideal for gathering the most nourishing parts of low-growing shrubs and other plants. In relation to their size, they also had the smallest brain of any dinosaur—the elephant-sized Stegosaurus had a brain that was no bigger than a dog’s. 75 About tails The vicious spikes at the tip of the tail could easily kill an attacking hunter. H u a ya n go s a u r u s r us Sh 76 o ur pt Si r us u s no r au Although built like a bird, Caudipteryx had short front limbs and could not fly. Pa t a g o t i t a n x er y no sa Big muscles attached to the base of the tail helped power the dinosaur’s legs. i p t e r yx The biggest dinosaur yet found had a slender, mobile tail tip for flicking enemies aside. Sp L e so t h o s a u Ca u d The weight of its tail helped Spinosaurus keep its balance on land and in water. i no u sa Caudipteryx had a short, stiffened tail with a distinctive fan of feathers. us Whether long, spiked, clubbed, or feathered, dinosaur tails had different uses. Most of the big dinosaurs had long, bony tails equipped with powerful muscles. These heavy tails helped to balance the weight of the dinosaur’s head and upper body. This was Traces of color cells in the fossils of this small hunter show that its tail had a pattern of light and dark bands. The sharp spikes on the tail made it an effective weapon for defense. especially important for dinosaurs like Xiongguanlong that walked on their hind legs. The giant sauropod Patagotitan, however, could sweep its long tail sideways like a whip with enough speed and force to knock a predator off its ny tail clu Delicate feathers b FEATHERED EVIDENCE Bo Four tail bones were fused together to form a formidable clublike weapon. E u o p l o ce p h a Most of our knowledge of dinosaurs comes from their bones. But this lump of ancient amber (hardened tree resin) contains the entire tail of a small theropod dinosaur, complete with muscles and brown feathers. The tail of this predatory dinosaur was mainly used for balance. Sinosauropteryx had the longest tail of any known theropod The tail was made of separate bones called vertebrae, forming a flexible chain. Xio ngg uan lus long Co r y t h o sa u r u s relative to its body. feet. The tail of Huayangosaurus was armed with two pairs of sharp spikes at the tip that made it a formidable weapon; the midsized sauropod Shunosaurus had a similar adaptation. Some ankylosaurs like Euoplocephalus had a massive, bony tail club that could be slammed into an enemy like a sledgehammer, shattering its bones. Some small theropod dinosaurs like Caudipteryx had short, bony tails with long feathers, just like modern birds. They may have been used for balance or to attract a mate. 77 DEADLY SPIKES For a hungry predator like Ceratosaurus, which lived in North America and Europe about 155 million years ago, a big, slow-moving stegosaur like Dacentrurus would have made a tempting target. The tall spikes on the stegosaur’s back and tail certainly looked imposing, but could they cause any harm? Moving in to launch its attack, Ceratosaurus would soon find out—the hard way. A hole in the tail bone belonging to another Jurassic predator, Allosaurus, was found to be a perfect match with a Stegosaurus tail spike. It is likely that the stegosaur was defending itself from an attack by swinging its tail like a spiked club. Dacentrurus was equipped in exactly the same way, with two pairs of stout, sharp-pointed spikes at the end of its tail. If an enemy like Ceratosaurus tried to creep up from behind—a common predatory tactic—it would be in for a nasty shock. With a flick of its spiked tail, the stegosaur could inflict terrible damage, blinding or even killing the hunter outright. It might have been a slow-moving plant-eater, but Dacentrurus could look after itself. Ankylosaurs Pi na The tail was covered with sharp, bladelike plates. co s a ur us Sa urop elta The first dinosaur found in Antarctica The body was flat and wide, making it difficult for predators to attack. was the ankylosaur Antarctopelta. The remains of this dinosaur were discovered in Asia—it had a long body with rows of bony studs on its back. A n k yl o sa u r u s The tail club was formed from solid bone. S h aic ania la Ta r ur us The front legs were protected by a cluster of studs and plates. 80 Protected from head to tail, the tanklike ankylosaurs first appeared about 175 million years ago. They were slow-moving plant-eaters, so without their body armor, they would have been easy targets for predators. Early ankylosaurs such as Scelidosaurus had bodies covered with bony plates and studs strong enough to break the teeth of any attacking dinosaur. But as predators got bigger and more powerful, ankylosaurs such as Saichania developed thick armor that may have discouraged even the massive-jawed Hung aro sa ur us Hungarosaurus Ankylosaurus G a r g oy l e o s a u r us Armor plates protected the heads of some ankylosaurs. Sauropelta had long spikes on its neck. The bony plates were embedded in the thick skin. Ankylosaurus even had armored eyelids. S ce l i d o s a u r Like many ankylosaurs, only the belly was unprotected. tyrannosaurs. Like several others, including Ankylosaurus, Saichania also had a hefty tail club to swipe at predators, inflicting serious injury. Others, such as Sauropelta, had long shoulder spikes that may have been as much for show as for defense. Many had broad The beak of this ankylosaur ancestor had sharp edges for cropping plants. mouths, ideal for gathering plant food in bulk, without being too selective, much like modern elephants. Their bulky bodies contained big digestive systems for processing their fibrous diet. us Ankylosaurs Rows of spikes jutted from the sides of Hungarosaurus. Dinosaur defense The age of dinosaurs The bone-clubbed tail of this ankylosaur could do a lot of damage when swung at an attacker. Eu ce p oplo Supe h a l u s ta i l The size of six adult elephants, Supersaurus would have had few enemies. r s a u r u s s i ze Alx The spikes made this plant-eater look bigger and more dangerous than it really was. as au ru sc la w s Alxasaurus was armed with long, knifelike blades. 82 Life was dangerous for many dinosaurs. They faced powerful predators—fierce meat-eating theropods with huge jaws and big appetites. For a few giant dinosaurs like Supersaurus, their sheer size was enough to make hunters choose easier targets. Small dinosaurs could hide or run away from trouble, as was the case with the ostrichlike dinosaur Struthiomimus. The stiff bristles on the back of Heterodontosaurus may have deterred enemies like the quills of porcupines. The big plant-eater Kentrosaurus (“spiked lizard”) was r o do n H e t e bris t o tl Some of the frill spikes were about 24 in (60 cm) long. s ur u sa s e This small dinosaur’s back was covered with prickly bristles. Dinosaur defence ur us sp ik es or n sh ru au os ac yr Pa c sa ep tro c hy Ke n us l o sa u r head ha With its long legs, Struthiomimus could outrun most of its enemies. The reinforced skull of a pachycephalosaur could be used as a weapon in a crisis. St St ru th sp i o m ee i mu s d s The nose horn of Styracosaurus may have been up to 22 in (57 cm) long. The extra-long shoulder spikes protected it from side attacks. heavily armored with plates and spikes. It could use its spiked tail as a defensive weapon, just like the club-tailed Euoplocephalus, lashing out at an attacker. Styracosaurus had an impressive array of horns, which may have been useful in a tight corner. Others like Alxasaurus had long, curved claws on its hands that could inflict serious damage, and the bone-headed Pachycephalosaurus may have even charged its enemies head first. Sometimes attack was the best form of defense. Iguanodontians r Ou a no sa u r u s D r yo sa u r u s Ouranosaurus had a distinctive finlike sail extending down the spine. The sheep-sized Dryosaurus had long feet and slender, powerful back legs, suggesting it was a fast runner. The sharp-edged beak was used for gathering plant food. Te n o n t o sa u r u s C p am The three long, sharp claws on its hands would have enabled Tenontosaurus to swipe at a predator. 84 Among the very first dinosaur fossils to be discovered and scientifically identified was the tooth of an Iguanodon—one of the biggest plant-eating ornithopods. It was found in England in 1822, and given the name “iguana tooth” because of its similarity to the t o sa u r us The hand had a sharp thumb spike that may have been used to stab attackers or for ripping tough plants. much smaller leaf-shaped teeth of present-day iguana lizards. Later, many entire skeletons of Iguanodon were found, with at least 38 discovered at one site in France, so it was probably a very common animal 135–125 million years ago. But Iguanodon was one of Bulky body had plenty of space for a large stomach to process fibrous food. M u t t a b u r r a sa ur us Iguanodontians Fossils of this big dinosaur were found at Muttaburra in Australia. Many of these dinosaurs may have had comblike dorsal crests. Rh Igu od on The skull was narrow. sa ur us The back legs were longer and more powerful than the front legs, which helped support some of its weight. The long, heavy tail helped balance its large body. an a b do do n Ma nt Mantellisaurus had a short thumb spike. li el The back legs were twice as long as the front limbs. Rhabdodon many similar dinosaurs. They all had strong hind legs and shorter, weaker arms, and the smaller ones such as Dryosaurus may have walked on their hind legs. Many, including Tenontosaurus, Muttaburrasaurus, and the elephant-sized Iguanodon itself, were more heavily built and Iguanodon supported some of their weight with their forelimbs. Despite this, their hands were adapted for a variety of tasks, with hooflike middle fingers; a mobile grasping fifth finger; and a stout spike on the thumb that may have been used as a defensive weapon. 85 Plant-eaters Pro t o ce r at o All ceratopsians had closely packed cheek teeth for chopping up leaves. ps s Nig cu er s do aur plo us Di Diplodocus used its peglike teeth like a rake. This dinosaur had more than 1,000 teeth. onto m d E sa u r u s H a dr The front of the jaw supported a broad beak. 86 Plant-eating dinosaurs used their teeth in different ways. The long-necked sauropods and their relatives—animals like Diplodocus— had specialized front teeth for gathering plants. Some used their teeth like combs to strip leaves from the twigs of trees and bushes. Many do os au r not seem to have chewed their food, and just swallowed the leaves whole. Other plant-eaters like Edmontosaurus and Psittacosaurus had sharp beaks for gathering food, and specially adapted cheek teeth for chewing it. The teeth of some of these animals, such as Iguanodon, Ca m a r a s a u r u s a on Jaw closing muscles were attached to rigid cheekbones. Jaw joint Psittacosaurus Igu d no Most modern plant-eating animals chew their food. This involves grinding their teeth together using complex jaw movements—up and down, side to side, or forward and backward. The skulls and jaw bones of plant-eating dinosaurs show that some of these animals did the same. The jaws of Psittacosaurus and many hadrosaurs could slide forward and backward, and ankylosaurs could probably chew by moving their jaws from side to side, just like sheep. The leaf-shaped teeth were ideal for snipping leaves from the twigs. Re b b a c h i sa u r u s Iguanodon’s flattened teeth had serrated edges. The front teeth were specialized for cropping low-growing plants. The parrotlike beak was used to gather plant food and may even have been used to crack nuts. Ps it t ac os au ru s Hundreds of teeth formed a complex grinding surface. were saw-edged for cutting up leaves, but hadrosaurs such as Edmontosaurus had hundreds of teeth packed together to form a filelike surface, specialized for reducing leaves and other plant material to a pulp. This made food much easier to digest, so the hadrosaurs did not need to spend so much of their time eating. As with all dinosaurs, the old, damaged teeth were continuously replaced by new ones, so they never wore out. Jaws could slide forward and backward. Plant-eaters Camarasaurus’s long, peglike teeth were for raking through foliage. JAW MOVEMENT Hadrosaurs Saurolophus The unique head crest changed shape with age. Lambe o sa u r u s The crest tilted backward. The backwardpointing crest was up to 3 ft (1 m) long, and was supported by a hollow bone. Ed m on os t Some Edmontosaurus were flat-headed. au r us The snout was long and broad. Hadrosaurus was about 30 ft (9 m) long. Fossil evidence shows that Edmontosaurus had scaly skin with large bumps. Hadrosaurus 88 Hadrosaurs lived during the Cretaceous Period, between 100–66 million years ago. They roamed the forests and swamps of North and South America, Europe, and Asia. They were large plant-eaters, and many of them had a broad, ducklike beak that they used to Shantungosaurus crop leaves. Similar to earlier iguanodontians, but with more complex teeth and jaws, hadrosaurs had jaws lined with hundreds of teeth arranged like the teeth of a file. Grinding together, these teeth reduced tough plant food to a juicy, easily digested pulp, ensuring that a M a i a sa u r The back had a high, bony ridge. The helmetlike crest was brightly colored to impress potential mates. a The fossils of young Maiasaura show that like all young animals, it had a large head, eyes, and feet until the rest of the body caught up. Pa r a Hadro s sa u About 49 ft (15 m) in length, Shantungosaurus is the largest known hadrosaur. a Sh ophus aurol ry r us Hadrosaurs Co sa u tho ntu sa n go ur us The jaw was studded with more than 1,500 chewing teeth. r us Hadrosaurus was the first dinosaur to be unearthed in North America. hadrosaur, such as Edmontosaurus, got as much nutrition as possible from every mouthful. Many hadrosaurs, including Lambeosaurus, also had impressive crests on their heads that could have been used to attract mates or for temperature control. The crests of some, such The small front feet did not bear much weight. as Parasaurolophus, formed bony tubes that may have helped to amplify their calls, making them sound like trumpeting elephants. They lived in herds, calling to each other to stay in contact as they roamed the forests of the Cretaceous world. 89 Cool crests Parasaurolophus had the longest crest of any known dinosaur—about 3 ft (1 m) long. Corythosaurus means “helmet lizard,” referring to its large, helmetlike crest. Co r ytho sa u r u s A spectacular hollow crest extended from its nose and may have been used like a trumpet. This hunter’s crest extended for most of the length of its snout. ol op aur n ur os sa colorful skin. Some of the most spectacular crests belonged to hadrosaurs, such as Corythosaurus, Olorotitan, and especially Parasaurolophus. The bones of these crests were hollow—possibly to make their calls louder, since the chambers in the crests of us s 90 The skulls of many dinosaurs were equipped with bony features that may have supported impressive crests. The bones were probably extended by extra structures made of tough keratin, like the horns of cattle or sheep, or covered by ra hu Mo u Di ph o lo sa pho Pa lo ru s Two distinctive flat crests extended along the top of the snout. The skin covering the fan-shaped crest was probably patterned with bright colors. At the top of the skull was a thin sheet of bone that curled forward. yo Cool crests Cr lop ho sa u O t loro itan L a m b eo sa u r u s r us A bony ridge supported its crest of tough keratin. The unusual ax-shaped crest curved forward over the skull. Citi pa ti many hadrosaurs were linked to their nostrils. But hadrosaurs were not the only crested dinosaurs. Several predatory theropods had crests, too, including the double-crested Dilophosaurus and a dinosaur found in Antarctica, Cryolophosaurus. Crests were also a prominent feature of beaked, birdlike oviraptorids like Citipati. All these bony extensions were for show, much like the colorful feathers of many modern-day birds. Dinosaur eggs Sa u ro pod eg g This dinosaur egg was about the size of a basketball. The nest was a mound of earth lined with ferns and twigs. Mai nes a r u a as Tiny at first, young dinosaurs grew very quickly. Sa lta sa ur us Thousands of Saltasaurus eggs were found in one nesting site— they were laid 80 MYA. 92 Just like their closest living relatives, birds and crocodiles, all dinosaurs laid eggs. They had hard, chalky shells like birds’ eggs, and at some fossil sites, the ground is covered in shell fragments. Where the eggs are intact, they have clearly been laid in nests on the ground. The biggest dinosaurs such as the sauropods seem to have buried their eggs in warm earth, or in piles of warm, decaying vegetation like modern crocodiles. The warmth was essential to make them hatch. Many smaller, lighter dinosaurs like t S au COLOSSAL EGGS ro po de Hen’s egg Beibeilong’s egg mb 18 in (45 cm) long One of the largest-known dinosaur eggs belonged to a giant birdlike dinosaur called Beibeilong sinensis. The eggs were discovered in China in a nest that was 30 ft (9 m) wide. ap t n or est n y on c h o sa u r u s em A Stenonychosaurus baby would have had its head tucked between its legs— Stenonychosaurus was a feathered theropod dinosaur. o The eggshell was strong but thin enough to allow oxygen to get through to the embryo. b ry Ste Ov ir The yolk contained all the food required for the unhatched dinosaur. Dinosaur eggs r yo The eyes only opened when the dinosaur was ready to hatch. These fossilized eggs were found in the Gobi Desert of Mongolia. Found in clutches of up to 40, these titanosaur eggs are almost spherical. Titanosaur eggs Oviraptor kept their eggs warm by sitting on them, just as most modern birds do. We know this because the fossilized remains of the adult dinosaurs have been found sitting on their eggs. The long-armed, feathered theropod dinosaurs known as maniraptorans may even have used their long “wing” feathers to brood and protect their eggs. The adults of some dinosaurs such as the hadrosaur Maiasaura (“good mother lizard”) cared for their newly hatched young, bringing food for them and driving away predators. 93 DINOSAUR CRÈCHE Around 125 million years ago, a catastrophic mudflow or fall of volcanic ash in what is now eastern China overwhelmed a nest of baby Psittacosaurus. They were buried along with a half-grown adult, just 6 years old. Found in 2004, their fossils seem to prove that the babies were being cared for after hatching and that their carer might not even be their parent. Many modern animals, from songbirds to wolves, live in extended families where the half-grown young help their parents look after the babies. Some birds such as ostriches also lay their eggs in communal nests or guard their young in crèches. The Psittacosaurus nest contained a huge family of 34 young. It seems likely that they had more than one mother and that they were being looked after by a babysitter—probably the elder sister or brother of some of the babies. If so, such childcare may have been common among dinosaurs. Psittacosaurus was an early ceratopsian— an ancestor of animals like Triceratops. Maybe these horned giants looked after their young in the same way. Numerous small spikes lined the head, snout, and cheeks. Ac r o t h o l u s The age of dinosaurs Pachycephalosaurs Homalocephale Pachycephalosaurus The bony shelf was a distinctive feature of all pachycephalosaurs. S t eg o ce r a s Discovered in Canada in 2013, Acrotholus was about 6 ft (1.8 m) long. The big eye sockets indicate that these dinosaurs had good vision. The long horns may have been for display rather than fighting. St y gi lo mo ch Small hands were useful for collecting food. 96 Also known as “boneheads,” referring to their incredibly thick, strong skulls, pachycephalosaurs were unusual-looking dinosaurs. The largest of the boneheads was Pachycephalosaurus. Its skull alone, the biggest so far, was up to 16 in (40 cm) thick D r a co r e x The sharp beak was used to gather leaves, fruit, and possibly insects. and ringed with small, bony spikes. It is likely that the strong skull protected the animal’s brain from regular impact inflicted during fights with rivals over status. But not all pachycephalosaurs