children s illustrated encyclopedia Prehistoric Life · children s illustrated encyclopedia...

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20 MARINE REPTILESIchthyosaurs and plesiosaurs

22 CRETACEOUS WORLDOrnithischians • Iguanodon • Other herbivores • Cretaceous carnivores

24 THE END OF THE DINOSAURSMass extinction • Survivors

26 THE AGE OF MAMMALSRooters and browsers • Mammal giants

28 THE ICE AGESSpread of ice sheets • Mammoths • Human evolution

30 FUTURE EARTHGlobal warming • Species extinctions • Catastrophic eruptions • Asteroid impacts • Future continental drift

32 INDEX

C O N T E N T S

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CONTENTS

4 THE STORY OF THE EARTHGeological time periods • History in the rocks • Evolution • Drifting continents

6 THE ORIGIN OF THE EARTHThe Solar System forms •Young Earth

8 FIRST LIFEOrigins of life • Earliest life-forms • Cambrian “explosion” of life

10 EARLY MARINE LIFETrilobites • First fish • Life on land •First plants

12 COAL SWAMPSCarboniferous world • Amphibian to Reptile

14 PERMIAN WORLDAge of Reptiles

16 TRIASSIC WORLDGreat extinctions • The first dinosaurs

18 JURASSIC WORLDGiant sauropods and theropods • Pterosaurs

C O N T E N T S

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First published in 2009 by Orpheus Books Ltd., 6 Church Green, Witney, Oxfordshire OX28 4AW England

www.orpheusbooks.com

Copyright © 2009 Orpheus Books Ltd

Created and produced by Orpheus Books Ltd

Text Nicholas Harris

Consultants Professor Michael Benton, Department of Earth Sciences, Bristol University

Illustrators Julian Baker, Alessandro Bartolozzi, Tim Hayward, GaryHincks, Steve Kirk, Lee Montgomery, Steve Noon, Nicki Palin, SebastianQuigley, Alessandro Rabatti, Claudia Saraceni, Peter David Scott, Roger

Stewart, Thomas Trojer, David Wright

All rights reserved. No part of this book may be reproduced, stored in aretrieval 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.

ISBN 978 1 905473 53 3

A CIP record for this book is available from the British Library.

Printed and bound in Singapore

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PRECAMBRIAN

First modernhumans

Dinosaursextinct

First floweringplants

First birds

First mammalsFirst dinosaurs

First archosaurs

First mammal-like reptiles

First reptiles

First amphibians

First lobefin fish

First insects

First fisheswith jaws

First land plants

First jawlessfishes

First shellfish

Oldest fossilsFormationof Earth

C A M B R I A N

O R D OV I C I A N

S I L U R I A N

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CARBONIFEROUS

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T E R T I A R Y

QUAT ERNARY

P R E H I S T O R I C L I F E

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The events of the Earth’s history arerecorded in the rocks that formed at acertain time. When sediments such as sand,silt or mud turned to rock, the remains oflife-forms that lived at the same timebecame fossilized in the same rocks. Thusscientists can piece together evidence ofwhat the world was like in the variousgeological periods. Layers of sedimentaryrock represent every geological epoch,although there is no place on Earth whererocks from every period in geologicalhistory are found.

E V O L U T I O N O F L I F EScientists can work out when aparticular animal or plant lived byestablishing the age of the rocks in whichits fossil was found. Over geological time,the fossil history tells us, animals (as well asother forms of life) have, very gradually,changed. Fins, tails, wings or teeth may havedeveloped as part of a process by which ananimal adapts to its environment. Thisprocess is known as evolution, and plays avery important part in the course of theEarth’s history.

D R I F T I N G C O N T I N E N T SThe outer shell of the Earth is divided upinto large slabs, called tectonic plates.Theseplates, which include both the continentsand the floors of the oceans, move slowly ata rate of about one centimetre a year. Overgeological time, entire continents havewandered around the globe, colliding intoone another or drifting apart. About 200million years ago, they came together toform a single “super-continent” calledPangaea. There was no Atlantic Ocean, andthe Americas were jammed up againstAfrica and Europe. Since then, thecontinents have split apart, although somepieces, such as India and Asia, have collidedwith each other.

These three globesshow the movement ofthe continents overgeological time. Stillwidely separated 400 Ma (1), they hadcollided to formPangaea by 320 Ma(2). They split apartduring the Age ofDinosaurs, after 180 Ma (3).

How do we know that continental drift has taken place?Fossils, once again, provide the evidence. The discovery offossils of Lystrosaurus (left), a Triassic reptile, in South Africa,India and Antarctica proves that these lands were once joinedtogether (in Gondwanaland—see page 14). How else wouldthis land animal have come to live in all three places?

THE STORY OF THE EARTH

THE EARTH is 4600 million years old.This huge span of time is difficult to

imagine, so events in the Earth’s history aretherefore measured in geological time, spansof millions of years. A “recent” event ingeological time, for example, may havehappened in the last million years.Geologists divide time into three Eons:

the Archaean (“ancient”), from the origin ofthe Earth to about 2500 million years ago(Ma), the Proterozoic (“first life”) to 530Ma, and the Phanerozoic (“visible life”) tothe present. The Archaean and Proterozoicare often referred to together as thePrecambrian.The Phanerozoic is subdividedinto Eras: the Palaeozoic (530-250 Ma), theMesozoic (250-65 Ma) and the Cenozoic(65 Ma-present). The Eras are split intoPeriods, which are shown here (right).TheTertiary and Quaternary Periods arethemselves divided into Epochs.

A way to understand geological time is to imagine 4600million years of Earth’s history taking place in just 12 hours!The Precambrian would take up the first 10 1/2 hours. From theCambrian “explosion” of life (see page 8) to the present daywould take up 90 minutes. The dinosaurs became extinct only9 minutes ago. The entire history of humankind would makeup the very last second.

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Y O U N G E A R T HIn its early days, Earth was a barren planet,rather like the Moon is today. Unprotectedby an atmosphere, it was continuallybombarded by meteorites, millions of rockyfragments that careered around the youthfulSolar System. These crashed to the ground,some gouging out massive craters (aboveleft). The persistent bombardment may havecaused the Earth’s rocky surface to melt: theplanet became a global sea of extremelyhot, molten rock (above right and 3 opposite).Eventually the bombardment eased and thesurface cooled. But the newly solidifedsurface trapped gases beneath it.

The pressure built up and hydrogen,carbon dioxide, water vapour and nitrogenburst through the crust in volcanoes.Thousands of eruptions raged all over theglobe (below left and 4). The gases collectedto form a new atmosphere around theEarth. Water vapour rose to form the cloudsthat enveloped the planet (5).Soon, as the Sun’s intense heat began to

cool, rain started to fall. It must have beenthe longest storm the Earth has everknown. Water poured from the sky formany thousands of years until the basins inthe land filled up, becoming the greatoceans (below right and 6).


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THE ORIGIN OF THE EARTH

PLANET EARTH is one of eight planetsorbiting the Sun, one of billions of stars

in the Milky Way Galaxy, itself one ofbillions of galaxies in the Universe. TheUniverse came into existence 12-15 billionyears ago. A few billion years later ourGalaxy was formed, but it was not untilabout 4600 million years ago that the Sunand its family of planets, including Earth,made their appearance.

T H E S O L A R S Y S T E M F O R M SNo-one can say for sure how the Earth wasformed, but many scientists agree on a likelysequence of events. The Solar System startedout as a cloud of gas and dust drifting inspace (many other such clouds in theGalaxy are known to astronomers).Something—perhaps a series of shock wavesemitted from a star exploding close by—caused the cloud to clump together underits own gravity. A huge, whirling disc of gasand dust was set in motion (1). Matter felltowards the centre and became hotter anddenser than at the edge of the disc. Thiscore of intense energy was the beginningsof our Sun.Meanwhile, the fragments of dust

spinning around the core started to clumptogether, becoming at first small rocks, then“snowballing” into larger boulders, beforegrowing into chunks several kilometresacross, known as planetesimals. Theplanetesimals started to collide with oneanother, eventually building up to becomethe four rocky inner planets, Mercury, Venus,Earth and Mars, and the rocky cores of the“gas giants”, Jupiter, Saturn, Uranus andNeptune. Energy from the Sun (the “solarwind”) stripped away the gas thatsurrounded the inner planets (2). But thegiant planets lay beyond the solar wind’sfiercest blast and so held on to their thickatmospheres, which remain to this day.


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FIRST LIFE

THE FIRST LIFE on Earth appearednot on land but in the oceans. The

atmosphere was still thin, so there was notenough oxygen in the air to sustain life.Ultraviolet radiation, lethal to life-forms,was also still at dangerous levels. Neitherproblem affected life underwater.Life probably arose about 3800 million

years ago, although the earliest fossilevidence we have is 3500 million years old.No-one knows how life began, butscientists think that shallow, warm-waterpools at the edges of the oceans would havebeen the ideal environment for theformation of chemicals that wouldeventually become the building blocks oflife. The vital chemical reactions could havebeen triggered by lightning or the shockwaves of a meteorite impact.The earliest life-forms were the very

simplest kinds: bacteria. The oldest fossils areknown as stromatolites, bands of blue-greenalgae that grew in shallow water. It wasanother 2500 million years before complexlife forms, types of seaweed, first appeared.

The largest and fiercest of allCambrian creatures was the 60-centimetre-long Anomalocaris, aname meaning “odd shrimp”. Ithad a cloak-like body, two largeeyes set on stalks and a pair ofpincer-like arms. Other smallermarine life-forms had defences torepel such giant marine predators.Hallucigenia, which moved aboutthe sea bed on seven pairs ofstilts, had a row of defensivespines on its back. Wiwaxia washat-shaped, complete with tworows of dagger-like blades.

One of the Burgess Shale animalsmay be of particular significanceto us. It is Pikaia, named afternearby Mt. Pika. This small,worm-like creature had astiffening rod running the length ofits body—not quite a backbone,but very similar to one. It also hadmuscles arranged in V-shapedsegments, exactly the same as inmodern fish. Pikaia may havebeen an early ancestor of thegroup of animals calledvertebrates (animals withbackbones) to which fish, reptiles,birds and mammals such asourselves all belong. Recent fossilfinds from China show that fish,complete with gills but withoutjaws, swam in the oceans about530 million years ago.

By about 530 million years ago,the first animals with hard parts—shells or bony skeletons—beganto appear. Still confined to thesea, they included shellfish,corals, starfish, sponges andmolluscs. Now a great variety oflife-forms could be possible. This“explosion” of life took place atthe beginning of the CambrianPeriod. Fossils discovered in theBurgess Shale of British Columbia,Canada, show what the life in awarm, shallow sea in Cambriantimes must have looked like.Among the life forms that we arefamiliar with today, there weresome very strange-lookingcreatures. One, Opabinia,had five mushroom-likeeyes and a long,clasping “nozzle” tocatch prey.

The first known animals existed fromaround 580 million years ago. Fossils of soft-bodied sea creatures, among them sea pens,jellyfish, worms and crab-like animals, foundin the Ediacara Hills, Australia, giveevidence of life in the Precambrian (alreadysome five-sixths of the way through thestory of the Earth).


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KEY1 Opabinia2 Anomalocaris3 Pikaia4 Leanchoilia5 Aysheaia6 Hallucigenia7 Sanctacaris8 Alalcomenaeus9 Wiwaxia



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L I F E O N L A N DUntil about 450 million years ago, there wasno life on land. Blue-green algae may havebeen exposed to the air, or even washedashore, at low tide. Very gradually, theseminute plants may have acquired the meansto stay alive longer on land. A waxy skinevolved to prevent them from drying out,followed by simple roots to anchor them inplace. By the late Ordovician, plants hadgained a foothold on land. By the end ofthe Silurian Period, plants had branchingstems and water-conducting tubes (above).

Land plants were a plentiful food sourceand certain marine animals evolved to takeadvantage of it. The arthropods’ externalskeletons were ideal protection againstdehydration while out of the water. Theirjointed legs allowed them to scuttle overuneven ground. Insects and spiders becamethe first land animals. They, in turn, werefood for fish that lived near the water’sedge. Gradually, lobefins like Eusthenopteronevolved the ability to “crawl” on their finsin pursuit of prey (below). These fish mayhave been ancestors of the amphibians.

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EARLY MARINE LIFE

THE CAMBRIAN Period wasfollowed, 505 million years ago, by the

Ordovician Period. Many species died out,to be replaced by new ones in anotherevolutionary “explosion”. Trilobites firstappeared in the Cambrian and rapidlybecame, for the next 250 million years,some of the most numerous of all kinds.Trilobites were members of the arthropodgroup, (creatures with a hard externalskeleton and jointed limbs).

T H E F I R S T F I S HThe first fish, perhaps descendants of Pikaia(see page 9), had “armour” plating to protectthem from predators like the eurypterids.These were arthropods with large claws,some of which reached lengths of twometres. Arandapsis, known from fossils foundin Australia, was one of the earliest. It fed bysucking in scraps of other dead animalsfloating in the water. Such fish dominatedthe seas for 130 million years.

Fish developed rapidly during theSilurian and Devonian Periods, evolvingjaws, teeth and fins. The evolution of jawsand teeth allowed fish to become activepredators. Fins gave them greater speed andmanoeuvrability in the water. Two distincttypes of fish emerged: those with skeletonsmade of soft cartilage (like the sharks andrays of today), and those that had hard, bonyskeletons. This second group becamedominant in late Devonian seas and rivers.Some species with fleshy fins, called the

lobefins, lived in warm waters in Devoniantimes, feeding on lakeside plants. One, along, slender fish known as Eusthenopteron,developed lungs and could spend some timeheaving itself around out of the water.

Arandapsis, an armoured, jawless fish fromthe Ordovician Period.

A trilobite’s body was covered by a hard,jointed carapace (shield) divided into threelengthwise strips (its name means “threelobes”). Its legs allowed it to scuttle alongthe sea bed, or to paddle it through thewater as it swam. Having no jaws, it usedits legs to carry food to its mouth.

Some fish with jaws and fins grewto enormous sizes. Dunklosteuswas longer than 9 metres. Even itsskull was more than 2 metreslong. Instead of teeth, its jawswere lined with massive plates ofbone that sliced through its preylike guillotine blades.


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Massive trees, including Lepidendron, akind of lycopod or club moss, andCalamites, a large horsetail, dominated thecoal swamps. Dragonflies the size ofpigeons, giant cockroaches and two-metre-

long millipedes livedamong the branches.

Giant insects, like thisdragonfly, flourished in the

hot, damp forests, but wereprey for the swamp-dwelling

amphibians and reptiles.

The Carboniferous seas also teemed withlife. Sharks were the dominant predators.Stethacanthus had a strange, tooth-covered projection above its head.

A scene in North Americaabout 300 million years ago. A

group of Eryops, two-metre-longamphibians, wade ashore among thedense vegetation of the coal swamp.These heavy, lumbering creatures,probably spent most of their time in

the water. Meanwhile, the 20-centimetre-long Hylonomus(“forest mouse”), a lizard-likeearly reptile, looks on.

A M P H I B I A N TO R E P T I L ELurking in the waters of the Carboniferouscoal swamps were the first amphibians.These animals had evolved from fish, theirfins having become limbs with fingers andtoes. Ichthyostega, an amphibian that lived inthe tropics of Greenland (now a polarisland), had a fish-like head and tail as it stillspent time in the water, especially for thepurpose of laying its jelly-covered eggs.Eventually, some kinds of amphibian

evolved a way of reproducing on land, thusavoiding the need to return to the water.Animals like tiny Hylonomus laid hard-shelled eggs. They were the first reptiles.


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COAL SWAMPS

BY THE BEGINNING of theCarboniferous Period, plants had spread

across the world’s continents and hadevolved into many different kinds, includingmassive trees. About 350 million years ago,Europe and NorthAmerica were tropicallands. Hot, steamyjungles blanketed thelowlands. They areknown as the coalswamps.

The continual cycle of growth and deathof swampy vegetation produced thick layersof rotting matter that turned to peat, adense, dark soil. Over millions of years, thethick beds of peat, overlain by sediments,were compressed, eventually becomingrock. This we know today as coal.


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A G E O F R E P T I L E SReptiles of all kinds dominated the parchedPermian world. (Some species, likeMesosaurus, adapted to life, once again, inthe water. In future years, the strength andsize of marine reptiles would make themfearsome predators.) Land reptiles could beclassified into three groups, distinguished byopenings in their skulls. The anapsids, fore-runners of turtles and tortoises, had none.The synapsids, which dominated thePermian landscape, had one opening oneach side. Members of the third group, thediapsids, had two skull openings on eachside. This group gave rise not only tomodern lizards, snakes and crocodiles, butalso, in the Triassic Period, to the dinosaurs.

Synapsid reptiles were also known asmammal-like reptiles because they were theancestors of the mammals. The earliest kindsto evolve were the pelycosaurs. Some, likeDimetrodon and Edaphosaurus (above), werethree-metre-long giants that had great sailson their backs. These were made of skin,supported by long thin spines sticking upfrom the backbone. It is thought that theymay have acted as temperature regulators,the blood vessels in the skin quickly takingup, or giving off, the sun’s heat.The pelycosaurs were succeeded by the

therapsids, a group that included the five-metre-long, lumbering herbivore, Moschops.Equally slow-moving was the anapsidScutosaurus. Diapsids were still quite scarce.They included Coelurosauravus, a tiny glider,and fast-moving Protorosaurus.


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PERMIAN WORLD

DURING the Carboniferous Period, theEarth’s two great continents, Laurasia

(made up of parts of present-day Asia,North America and Europe) andGondwanaland (a combination of SouthAmerica, Africa, Antarctica and Australia)collided with one another, forming a singlehuge land-mass. Geologists call this“supercontinent” Pangaea. Much of southern Pangaea lay across the

South Pole during the early PermianPeriod. It was covered by an ice cap. A greatdeal of the Earth’s water was “locked up” inthe ice. This meant that for the rest of theworld the climate became very dry and hot.

The humid, tropical forests of theCarboniferous gave way to vast, dry scrub-lands and deserts. Large amphibiansdependent on water for breeding started todie out, while reptiles multiplied. Theirability to lay eggs on land allowed them tolive in dry environments. Besides strong legsand tough skin, they also developedpowerful jaw muscles, which enabled themto eat tough desert plants.


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KEY1 Coelurosauravus2 Moschops3 Protorosaurus4 Scutosaurus5 Edaphosaurus6 Dimetrodon



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The plant-eaters, or sauropodomorphs,emerged later, towards the end of theTriassic. One of the largest of these types ofdinosaur, the prosauropods, was the 10-metre-long Riojasaurus, also from southAmerica. Another was Plateosaurus, fromEurope (above). Eight metres long, itprobably spent some of its time on allfours, but most of the time walked and ranon its two long, powerful back legs.Plateosaurus may have used its large, curvedthumb-claw to pull down branches.Unable, like many dinosaurs, to chew itsfood, it swallowed stones which ground uptough plants inside its stomach, makingthem easier to digest.Not all plant-eaters were so enormous.

Mussaurus was from South America. Itsname, meaning “mouse lizard”, was givento it because the first skeleton to bediscovered was tiny. Scientists later realisedthat this skeleton was actually that of ababy. Adults grew to be three metres long.

One of the best-known of all Triassicdinosaurs was Coelophysis. A three-metre-long theropod, it lived in what is now thesouthern United States. Coelophysis had along, narrow head and sharp, saw-edgedteeth, which it used to devour lizards andother small prey. Large numbers of fossilshave been found together, suggesting thatCoelophysis lived in packs like wolves. Someskeletons contained the bones of theiryoung, suggesting that these dinosaursmight have been cannibals.

Coelophysis wasa slender-bodieddinosaur, builtfor speed.

Euparkeria was anarchosaur, aforerunner of thedinosaurs. It couldrun on its hind legs.

KEY1 Eudimorphodon2 Kuehneosaurus3 Plateosaurus4 Ornithosuchus5 Saltopus

KEY1 Riojasaurus2 Herrerasaurus3 Mussaurus

South America in the Triassic Period.

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TRIASSIC WORLD

THE TRIASSIC PERIOD began at atime, 250 million years ago, when a

vast number of animals, both on land and inthe sea, became extinct. Scientists are unsurewhy, although the extreme hot and dryclimatic conditions across the continent ofPangaea may have been responsible. A number of reptiles survived the

extinctions, however, including themammal-like reptiles. Lystrosaurus, a tusked,pig-like reptile, spread rapidly (see page 5).Another group of reptiles began to achievedominance at this time. With their powerfuljaws and bony armour, the archosaurs, fromthe diapsid group, quickly multiplied. Earlyarchosaurs had a low, sprawling gait (likemodern lizards), but, as the Triassic went on,some kinds began to stand more upright.The powerful runner Ornithosuchus, forexample, had a short body with a long,counter-balancing tail and strong hind legs.By the late Triassic, some archosaur speciesmoved around on two legs all the time.They were the first dinosaurs.

T H E F I R S T D I N O S A U R SThe first known dinosaurs appeared about230 million years ago in the southern partof South America and in southern Europe.In Triassic times, both these regions lay onthe fringes of Pangaea, a lush landscape—incontrast to the supercontinent’s aridinterior. These early dinosaurs were smalltheropods (meat-eaters) which ran on twolegs. Herrerasaurus, from South America, hada flexible neck, large, eyes, sharp teeth and along tail, which acted as a balance. Its strongback legs left its arms free to grasp its prey.


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To defend themselves against thesefearsome predators, some plant-eatersdeveloped armour. Stegosaurus, a 10-metre-long, slow-moving dinosaur from NorthAmerica, had a double row of diamond-shaped bony plates running the length of itsback. It also possessed several long spines atthe end of its tail, with which it could lashout at its attacker.

Alongside the massive Jurassic dinosaurslived some of the smallest dinosaurs known.No bigger than a cat, Compsognathus was along-legged, fast-moving predator, feedingon lizards and other small creatures it chasedthrough the undergrowth. Fossils of itsskeleton show that it had a very similar buildto Archaeopteryx, one of the earliest-knownbirds, which lived in the same region,Europe, and at the same time, 150 millionyears ago, as Compsognathus. Recent evidencethat some dinosaurs may have beenfeathered supports the widely-held view thatbirds are descended from dinosaurs.The birds were not the first vertebrates to

fly, however. Flying reptiles, known aspterosaurs, had first taken to the air millionsof years earlier during the Triassic Period.Rhamphorhynchus and Pterodactylus weremarine predators in the Jurassic.

Sheets of skin between the fourth fingerand the body made up a pterosaur’s wings,Many had powerful, toothed beaks thatwere perfect for seizing, and holding on to,fish they caught while skimming the surfaceof the sea. The Jurassic saw the emergence of a new

kind of dinosaur. The sauropods andtheropods were saurischian, or lizard-hipped, dinosaurs: their hip bones wereshaped like those of other reptiles. Now anew group, the ornithischians, or bird-hipped dinosaurs, madetheir appearance. Theirhip bones were shapedlike those of modernbirds (although,confusingly, birds werethemselves descendedfrom the saurischiankind). Equipped withthe ability to chew theirfood, these plant-eatersquickly multiplied,taking advantage of theever-increasing varietyof plants found in thelate Jurassicenvironment.


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DURING JURASSIC times, from 208to 144 million years ago, the super-

continent of Pangaea began to split in two:Laurasia and Gondwanaland started to driftapart again. The climate, while still warm,became much wetter. Sea levels rose,causing widespread flooding of low-lyinglands. Plants, especially coniferous trees,became abundant, providing a rich foodsource for the dinosaurs, now the only largeland-living animals.Sauropods took over from prosauropods

as the dominant plant-eaters, culminating insuch giants as Diplodocus and Brachiosaurus,among the longest and largest land animalsthat have ever lived. These enormouscreatures, measuring more than 20 metreslong, had very long necks and equally long,whip-like tails to balance them. Their teeth,shaped like pegs (in Diplodocus andBrachiosaurus) or spoons (in Cetiosaurus andCamarasaurus), were perfectly designed fortearing off leaves from trees.As the sauropods became larger and more

numerous, so the meat-eating theropodsbecame more powerful hunters, capable ofbringing down a 20-metre sauropod, either

individually or hunting in packs.Megalosaurus, from Jurassic Europe, wasabout nine metres long. Equipped withpowerful jaws, it was able to attack evenquite large sauropods. (Megalosaurus was thefirst dinosaur to be discovered and, in 1824,to be given a name.) Top predator in NorthAmerica at the same time was 12-metre-long Allosaurus. It may have hunted in packsto attack Diplodocus. Any prey trapped in itsbackwards-curving teeth would have foundit hard to escape.

Stegosaurus wasa plant-eatingdinosaur. It mayhave been ableto rear up on itsback legs tofeed from trees.

KEY1 Cetiosaurus2 Megalosaurus3 Echinodon4 Compsognathus

Fossils of all theseflying creatures havebeen found in rocksof the Jurassic Periodin Germany.

Humanbeing (at

same scale)

Rhamphorhynchus

Pterodactylus

Archaeopteryx

Brachiosaurus is the largestdinosaur known from a completefossil skeleton. At 14 metres tall,it would have been able to lookinto the top-floor window ofa four-storey building! Itused its long neck totear leaves fromhigh in thetrees.


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JURASSIC WORLD



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The Jurassic Period saw the emergence ofanother important group of marine reptiles:the plesiosaurs. Like dinosaurs, they hadlong necks and small heads. Instead of legs,their limbs had become large, paddle-likeflippers which they used like underwater“wings” to pull themselves through thewater, beating in a slow, steady rhythm.Plesiosaurs fed on fish and squid, dartingtheir long, flexible necks backwards andforwards to pick off their prey. They spentmost of their time in the water, comingashore only to lay their eggs.

By the late Cretaceous, some plesiosaurshad become giants. Elasmosaurus was 14metres long—with a neck more than half itsbody length. It could have held its headclear of the water, hunting for prey from ahigh vantage point (below).


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MARINE REPTILES

WHILE the dinosaurs ruled the landand the pterosaurs circled in the

skies, reptiles also dominated the seas. Somekinds of reptile began to feed on marine lifeduring the Triassic Period, and gradually thebody design of marine reptiles adapted toan underwater lifestyle. One of the earliest marine reptiles,

Placodus, lived in shallow coastal waters.Apart from its long, fishy tail, it looked verymuch like a land reptile, with its short neck,heavy body and sprawling legs. It used itspowerful jaws to crush shellfish. Long-necked Nothosaurus was a more streamlinedswimmer, spending its time resting on land

and feeding in the water in the same waythat seals do today. Henodus was quitesimilar to a modern turtle. Its bony-platedshell protected it from attack by predators. Atoothless beak was designed for breakingopen shellfish.The best-adapted ocean reptiles were the

ichthyosaurs, such as Ichthyosaurus (below).They were at their most abundant duringthe Jurassic Period, a time when shallow,warm seas covered much of the Earth. Likemodern dolphins, ichthyosaurs wereperfectly streamlined, with long flippers forsteering and strong tails to propel themthrough the water. They were the firstmarine reptiles to spend all of their time inthe water. They gave birth to live young.


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KEY1 Nothosaurus2 Placodus3 Henodus

Giant pterosaurs andplesiosaurs scour theseas for prey in thisCretaceous scene.



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O T H E R H E R B I V O R E SThe Cretaceous Period also saw theemergence of the hadrosaurs, ornithischiandinosaurs that had cheek teeth whichcontinually replaced old, worn ones. Itenabled them to take full advantage of theplentiful vegetation that grew in lateCretaceous times.Armoured dinosaurs also evolved many

different forms. The ankylosaurs wereformidable, tank-like dinosaurs, coveredwith rows of hard, bony plates and spikes. Ifthis were not enough to deter an attacker,ankylosaurs like Saichania, from Mongolia,had a large ball of bone at the end of theirtails which they could swing like clubs.

C R E TA C E O U S C A R N I V O R E SDuring Cretaceous times, a variety of newpredatory dinosaurs appeared, some verylarge, like Carnotaurus, and some relativelysmall, like the dromaeosaurs. Hunting inpacks, Deinonychus, a three-metre-longdromaeosaur from North America couldbring down larger prey using its hooked,slashing foot-claws. Other predatorsincluded the ornithomimids, intelligent,fast-running hunters of small prey, and thegiant tyrannosaurs (see page 24).


23

CRETACEOUS WORLD

THE CRETACEOUS PERIOD wasthe heyday for the dinosaurs. Laurasia

and Gondwanaland, the northern andsouthern halves of Pangaea, themselvesstarted to break up into smaller land-masses.These would later become the continentswe know today. The climate remained aswarm and humid as in Jurassic times, and awide variety of plant life grew in all parts ofthe world—including Antarctica, today afrozen wasteland. Flowering plants,including deciduous trees, which hadevolved during the Jurassic, replaced somemore ancient plant species.The abundance of plant food favoured

new kinds of ornithischians. They becamemore abundant during the early Cretaceous,while many of the massive, long-neckedsauropods, such as Brachiosaurus andApatosaurus, died out. Unlike the slow,lumbering sauropods, many of these newkinds were small, fast-moving dinosaurs.Like gazelles, when danger threatened, aherd of Hypsilophodon, from CretaceousEurope, would sprint for safety.

I G U A N O D O NIguanodon, a considerably larger animal(nine metres long), was much less nimblethan Hypsilophodon, relying instead onanother means of defence. As well as itsclawed fingers, Iguanodon had a large,viciously sharp thumb-spike, which it couldhave jabbed into the neck of any predatorydinosaur. Herds of Iguanodon roamedtropical forests the world over.

Iguanodon probablywalked on all fours,rearing up on its hind legsto run at speed, to feed onleaves high in the trees or tounleash its thumb-spike inself-defence. Whenfeeding, its toothless beakwould nip off the leaves,while its cheek teethchewed them up beforeswallowing.

Baryonyx (below) was an unusualtheropod dinosaur from CretaceousEurope. It had the body of a largecarnivore (6 metres long), but itsskull was long and narrow, withmany small, sharp teeth—morelike that of a crocodile. Baryonyxprobably fed on fish, wadingthrough the shallows and hookingout its prey with its long thumb-claw, after which it is named(“heavy claw”).

Deinonychus,whose namemeans “terribleclaw” hadgrasping clawsas well as deadlyfoot-claws.

Parasaurolophuswas a hadrosaur.The crest on itshead may haveamplified itswarning calls.

Ornithomimus, about 3.5 metreslong, could run at 50 km/h on itslong, powerful legs.


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KEY1 Gallimimus2 Saichania3 Oviraptor4 Protoceratops



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M A S S E X T I N C T I O NThe dinosaurs, the pterosaurs, all marinereptiles and a large number of other speciesall died out at the end of the Cretaceous.No-one yet knows why this was so, but theevidence shows that the event was quiteabrupt. It is thought by some scientists thata massive asteroid (a large rocky object inspace) may have crashed into Earth (above).The resulting explosion may have filled theatmosphere with dust, blotting out the sunand lowering temperatures for years on end.

By another theory, a massive volcaniceruption could have taken place on Earth,blasting millions of cubic kilometres of lavainto the atmosphere, producing the sameeffect on the climate as an asteroid collision.Evidence for both theories comes from

the discovery by geologists of a layer ofmetal, called iridium, in late Cretaceousrocks. This metal is believed to be present inthe core of the Earth and in asteroids, butnowhere else. Iridium dust thrown up by anexploding asteroid or lava from inside theEarth may have settled on the surface, thenlater compacted in the rocks of the time.

S U R V I V O R SWhile the dinosaurs and others perished, anumber of reptile species survived theextinction, including lizards, snakes,crocodiles and turtles. But the disappearanceof the dinosaurs and pterosaurs offered anopportunity for mammals to become thedominant land animals, and for birds to rulesupreme in the air.Mammals had evolved from mammal-like

reptiles back in the Triassic Period, 225million years ago. They had fur on theirskins, enabling them to become warm-blooded. But, while dangerous dinosaurpredators were about, they remained tiny,shrew-like animals venturing out only atnight to feed. Their time had now come.


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THE END OF THEDINOSAURS

BY THE END of the Cretaceous Period,about 65 million years ago, all the

dinosaurs were extinct. They had ruled theland for more than 160 million years (bycomparison, anatomically modern humanshave existed for just 125,000 years).Although birds and mammals had evolvedduring the Age of Dinosaurs, no other largeland creatures, save crocodiles, which spentmost of their time in rivers, existed.The last years of the dinosaurs produced

some of the most spectacular kinds. Of theplant-eaters, the hadrosaurs, such asLambeosaurus and Pachycephalosaurus, werevery numerous, but they were joined by anew group, the ceratopians, the horneddinosaurs. In North America, for the last 20million years or so of the dinosaurs’ reign,they were the most abundant largeherbivores on Earth. Animals like the nine-metre giant Triceratops had a huge skull, amassive neck frill for self-defence longhorns and a parrot-like beak.

Megazostrodon was one of the first mammals.It was an insect-eater, just 5 cm long.

A Tyrannosaurus and Triceratops confrontone another in North America 70 millionyears ago. Although Triceratops’ neck frillgave it some protection from attack, theteeth of Tyrannosaurus were sharp enoughto penetrate the herbivore’s scaly skin.

Small mammals explore the skeleton of aTriceratops. The Age of Dinosaurs is over.

Only the largest, most powerful predatorwould have been a match for Triceratops.Unfortunately for Triceratops, just such amonster existed:Tyrannosaurus rex. Thisawesome, 12-metre-long killing machinehad massive powerful back legs which gaveit great speed over short distances. It had anenormous head, with jaws surrounded byrows of saw-edged teeth, some up to 18centimetres long. Only its arms were puny,but had they been longer, the dinosaurwould have over-balanced. Tyrannosaurusprobably made its kill by charging its prey,bringing it down with devastating bites. Itmay also have scavenged the kills of others.


24



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By the time the dinosaurs becameextinct, several different groups of mammalshad already evolved around the world.During the Palaeocene and early EoceneEpochs, the climate was warm and tropicalrainforest was widespread, even at the poles.Mammals that were best suited to movingthrough dense trees dominated.

R O OT E R S A N D B R O W S E R SThe mammals of the Palaeocene wereforest-dwellers. They included a number ofspecies that look unfamiliar to us today.Some roamed the forest floor seeking plantstems or roots. They included the strange,knobbly-headed Uintatherium or twin-horned Arsinoitherium. Others, such asrodents and primates, browsed for leavesand fruits in the trees themselves.No large carnivorous mammals then

existed. But among the birds, which hadalso developed into a wide variety ofspecies, were some predatory giants—forexample, the three-metre-high, ground-dwelling Diatryma from North America.With its enormous, bone-crushing beak,Diatryma feasted on mammals, includingeven small, primitive horses!

M A M M A L G I A N T SDuring the Oligocene Epoch, the climatebegan to cool. Ice caps formed at the polesand many dense forests were replaced bymore open woodland. The forest-dwellersgave way to much larger mammals thatthrived in these conditions. They includedIndricotherium, a massive rhinoceros fromCentral Asia, and Andrewsarchus, an earlymammalian carnivorous giant.By the Miocene, vast areas of grassland

had opened up, leading to the evolution offast-running horses and antelopes, as well aspredatory dogs, cats and hyenas. Massiveelephants, adapted to feeding from trees ongrasslands, evolved. Meanwhile, some fish-eating carnivores developed the ability tospend more time in the water, and evolvedinto the group we now call the whales.


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THE AGE OFMAMMALS

AFTER THE DRAMATIC extinctionsat the end of the Cretaceous Period,

the Earth entered what is known as theTertiary Period. It is divided into a numberof Epochs (see page 4) beginning with thePalaeocene and finishing 1.8 million yearsago as the Ice Ages dawned.By the beginning of the Tertiary, the

continents had drifted to approximatelytheir present positions, although North andSouth America were still separated. Eachcontinent, with the exception of Australiaand Antarctica which were still linkedtogether, had become an isolated land-mass.This meant that early mammals evolvedseparately on their own island continent.

This is a map of the world during Eocenetimes (part of the Tertiary Period), about50 million years ago (above). The paleblue areas are shallow seas, tracts of landthat have been submerged beneath highsea levels.

This is what a region of North Africa, todaybarren desert, would have looked like 35million years ago (below). Living in theswamps were the early elephant Phiomia,the rhinoceros-like Arsinoitherium and aprimitive ape Aegyptopithecus.

KEY1 Aegyptopithecus2 Arsinoitherium3 Phiomia

Indricotherium was a tree-browserabout 30 million years ago. About5 metres high at the shoulder, itweighed as much as 10 modernrhinoceroses. It was thelargest land mammalthe world has everseen.

Andrewsarchus(below, left) was

the largest-knownflesh-eating mammal

that walked on land. Itwas 4 metres long,

nearly a metre of whichwas taken up by its

massive skull. It may haveresembled a large hyena.Andrewsarchus lived inMongolia about 40 millionyears ago, where it probablylived by scavenging.


26

Human(to scale)



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Mammoths are the best-known Ice Agemammals. Woolly mammoths (below), withtheir shaggy coats and layers of body fat,were well suited to the cold, summer-lessenvironments of the north. They roamedthe northern tundra lands until about10,000 years ago (although a small numbersurvived on a Siberian island until just 3500years ago). Complete carcasses, preserved inice, are still found today. Climatic changeprobably finished them, but they may havebeen hunted to extinction by humans.

H U M A N E V O L U T I O NHuman-like animals, called hominids, firstappeared about four million years ago, butthe evolution of modern human beingstook place during the Ice Ages. The fossilevidence points to the grasslands of Africabeing our place of origin, from wherehumans spread out to all parts. One branchof the hominid group, called Neanderthals,adapted to the cold European climate, butdied out 30,000 years ago.


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THE ICE AGES

THE QUARTERNARY Period runsfrom about 1.8 million years ago to the

present. The Pleistocene Epoch, whichoccupies all but the last 10,000 years, wasthe time of the Ice Ages, during which, onat least four occasions, great ice sheetsspread southwards and buried much ofnorthern Europe, North America and Asia.In between, there were periods of warmer,even subtropical, climate, called interglacials.

This is a map of the world as it was40,000 years ago, at the height of the IastIce Age during the Pleistocene Epoch. Thewhite areas show the ice caps. Today, icecaps cover the Arctic Ocean, Greenlandand some of the islands of NorthernCanada. During the Ice Ages, ice capsstretched much further south. The ice“locked up” a great deal of the world’swater, resulting in lower sea levels.

Coelodonta, the Ice Age woolly rhinoceros.

Gigantopithecus was a massive ape,standing about 2.5 metres tall. Itroamed the forests of China in IceAge times, feeding on leaves.Some say this ape is theorigin of the Yetilegend.

Most of North Americaand northern Europelooked like this40,000 years ago.The ice was 3 kmthick in places.The advancing icegouged outvalleys, smoothedover hills and plainsand filled rock basinswith water, forminglakes, when they melted.


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The Pleistocene Ice Ages are not the onlyones in the history of the Earth. A majorIce Age occurred in the late Carboniferousand early Permian Periods, about 290million years ago (see page 14). Today’sclimates are generally cooler than on manyoccasions in prehistory, so it is quite possiblethat we are living through an interglacial. Afifth Ice Age may one day grip the world.It is not clear what causes an Ice Age. It

may be that the Earth’s angle of rotationchanges slightly, tipping the poles furtheraway from the sun’s rays.

The Ice Ages had a major effect on theworld’s climate, and its wildlife experiencedmajor changes, too. During the warmerinterglacials, animals like elephants,hippopotamuses and hyenas could migratenorthwards. When the ice sheets spreadsouthwards, mammoths, rhinoceroses,reindeer and bears adapted to life in the vastregions of tundra, treeless areas of lowgrasses and frozen soils. Some migratedsouth in winter, others hibernated.



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In the longer term—millions of yearsinto the future—the Earth itself willcontinue to change. Rivers and glaciers willerode upland areas, creating new lowlands.These may then be uplifted, creating, inturn, new uplands. The continents will goon drifting around the globe, creating ordestroying land-masses and ocean floors.Despite the probable destruction of anumber of living environments by humans,life will go on evolving.


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FUTURE EARTH

THE EARTH is 4600 million years oldand is expected to have a natural life of

another 5000 million years. What will thefuture hold? Living things, in one form oranother, have existed for at least 3500million years, undergoing constant changeand evolution. What will future living thingsbe like? How long will humans survive?In the short term, the one thing scientists

are agreed upon is that the Earth willbecome much warmer. This is known asglobal warming. The average temperaturehas risen by more than 0.5˚C in the pastcentury. This is predicted to rise to 2˚C by2050. The effects may be felt as moreviolent storms, shifting rainfall patterns andrising seas, which could submerge many ofthe world’s coastal areas. Many scientistsbelieve that the the emission of certaingases—chlorofluorocarbons (CFCs), carbondioxide and methane—from factories, cars,and power stations may contribute to the“greenhouse effect” (above right), a likelyreason for the rise in global temperatures.

The Earth’s surface and its cloudsboth absorb sunlight, beforereleasing it back into space.Some gases trap part of thisoutgoing heat in the atmosphere,keeping the surface warm—justlike a greenhouse. Increasinglevels of these so-calledgreenhouse gasesmay warm theEarth too much.

Another change we are likely tosee over the next 50-100 yearsis the extinction of somefamiliar mammals. The tiger, forexample, is already endangeredbecause of severe reduction ofits natural habitat in Asia.

The discovery of new planets around otherstars raises the possibility that we mightone day encounter life from other worlds.Will extra-terrestrial life-forms look likethis, the popular idea of an alien? Whatwill be the impact on us and our planet?

The impact of a large asteroid collidingwith Earth would be catastrophic. Overmillions of years, it is bound to happen ...

Volcanic eruptionsoccur all over theEarth. Occasionally, amajor eruption maythrow up so muchmaterial into theatmosphere that theclimate is affected.This could have ledto the extinction ofthe dinosaurs. Couldit happen to us?


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Present-dayposition of the

continents shown in blue.

How will humankind cope with thischange? The reduction of greenhouse gases,by a switch to alternative forms of energy,could arrest global warming. A newapproach to conservation may save somewell-known species from immediateextinction. In the longer term, it wouldseem very little could save our planet froman asteroid impact or cataclysmic volcaniceruption. The search for new planets toinhabit may provide a safe haven for peopleto survive such a catastrophe.

This is how the world may look 50 millionyears from now. The Atlantic Ocean hasspread apart. North and South America areno longer joined together and Africa andAsia have split at the Red Sea. Australiahas collided with Indonesia.

Reflected byclouds

SunlightReflected

byatmosphere

Reflected byground

Absorbed byground

NORTHAMERICA

SOUTHAMERICA

EUROPE

AFRICA

ASIA

AUSTRALIA

AtlanticOcean

PacificOcean

IndianOcean



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A BAegyptopithecus 26Alalcomenaeus 8algae, blue-green 8, 11Allosaurus 18amphibians 4, 11, 13, 14anapsids 15Andrewsarchus 27animals 8, 11 ankylosaurs 23Anomalocaris 8Apatosaurus 22Arandapsis 10Archaean Eon 4Archaeopteryx 19archosaurs 4, 16Arsinoitherium 26-27arthropods 10-11asteroid collision 25, 31atmosphere 7, 8, 25, 30Aysheaia 8Baryonyx 23birds 4, 19, 25, 27Brachiosaurus 18, 22

CCalamites 13Camarasaurus 18Cambrian “explosion” of

life 4, 8 Cambrian Period 32, 36,

38Carboniferous Period 4,

12-13, 14, 28Carnotaurus 23Cenozoic Era 4ceratopians 24Cetiosaurus 18climatic change 14, 16, 18,

25, 27, 28-29, 30coal swamps 12-13Coelodonta 28Coelophysis 17Coelurosauravus 15Compsognathus 18-19conservation 31continental drift 5, 18, 31craters 7Cretaceous Period 4, 21,

22-23, 24-25, 26

DDeinonychus 23deserts 14, 16Devonian Period 4, 10diapsids 15, 16Diatryma 27Dimetrodon 15dinosaurs 4, 15, 16-17,

18-19, 22-23, 24

LLambeosaurus 24Laurasia 14, 18, 22lava 25Leanchoilia 8Lepidendron 13life-forms, first 8, 11lightning 8lycopod 13Lystrosaurus 5, 16

M Nmammals 26-27evolution of 25, 26-27, 28-29

first 4, 24-25mammoths, woolly 29marine life 10-11, 13,

20-21Megalosaurus 18Megazostrodon 24Mesosaurus 15Mesozoic Era 4meteorites 7, 8millipedes 13Miocene Epoch 27Moschops 15Mussaurus 16-17Neanderthals 29Nothosaurus 20

Oocean floor 5, 31oceans 7, 8Oligocene Epoch 27Opabinia 8Ordovician Period 4,

10-11ornithischian dinosaurs 19,

22-23ornithomimids 23Ornithomimus 23Ornithosuchus 16-17Oviraptor 22

P QPachycephalosaurus 24Palaeocene Epoch

26-27Palaeozoic Era 4Pangaea 5, 14, 16, 18, 22Parasaurolophus 23particles, high-energy solar

6peat 12pelycosaurs 15Permian Period 4, 14-15,

28Phanerozoic Eon 4Phiomia 26Pikaia 8-9, 10Placodus 20plants, first 4, 11first flowering 4, 22

Plateosaurus 17Pleistocene Epoch 28

extinction of 4, 24-25, 30

first 4, 16fossils of 19

Diplodocus 18dragonflies 13dromaeosaurs 23Dunkleostus 10

EEarth, early years 7formation of 4, 6-7future of 30-31history of 4-5, 6-29surface temperature of 30

Echinodon 18Edaphosaurus 15Ediacara Hills 8Elasmosaurus 21Eocene Epoch 26-27Eryops 13Eudimorphodon 17Euparkeria 16eurypterids 10Eusthenopteron 11evolution 5, 10, 29, 30extinctions 16, 24-25, 29,

30

F Gfish 4, 9, 10, 11 floods 18fossils 4-5, 8, 9, 17, 29Gallimimus 22geological time 4-5Gigantopithecus 28glaciers 31global warming 30-31Gondwanaland 5, 14, 18,

22grasslands, emergence of

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Hhadrosaurs 23, 24Hallucigenia 8Henodus 20Herrerasaurus 16Homo sapiens 29humans 4, 29 Hylonomus 13Hypsilophodon 22

I J KIce Ages 28-29 ice caps 14, 27, 28Ichthyosaurus 20Ichthyostega 13Iguanodon 22Indricotherium 27insects, first 4interglacials 29Jurassic Period 4, 18-19,

20-21Kuehneosaurus 17

plesiosaurs 21Precambrian 4, 8prosauropods 17Proterozoic Eon 4Protoceratops 22Protorosaurus 15Pterodactylus 19pterosaurs 19, 20-21, 25Quarternary Period 4, 28

Rrainfall 7, 30reptiles 4, 13, 14-15flying 19mammal-like 15, 16, 25marine 15, 20-21, 25

Rhamphorhynchus 19Riojasaurus 16-17

SSaichania 22-23Saltopus 17Sanctacaris 8saurischian dinosaurs 19sauropodomorphs 17sauropods 18-19, 22Scutosaurus 15sea levels, rising 30seaweed 8sedimentary rocks 5sediments 5, 12sharks 13Silurian Period 4, 10-11solar wind 6Solar System,

formation of 6Stegosaurus 18-19Stethacanthus 13storms 7, 30stromatolites 8Sun 6, 30synapsids 15

T U VTertiary Period 4, 26therapsids 15theropods 16-17, 18-19,

23Triassic Period 4, 15,

16-17, 20, 25Triceratops 24-25trilobites 10tropical climate 12, 27tyrannosaurs 23Tyrannosaurus rex 24-25Uintatherium 27ultraviolet rays 8valleys 28vertebrates, first 9volcanic eruptions 7, 25,

30-31volcanoes 7

Wwhales, evolution of 27Wiwaxia 8

I N D E X

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INDEX Page numbers in bold

refer to main entries.


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