EVOLUTION ORIGIN ANDBEYOND

Gould, who alerted him to the fact the Galapagos finches ORIGIN ANDBEYOND were distinct but closely related . Darwin investigated (1823–1913) the breeding and artificial selection of domesticated , and learned about species, time, and the record from despite the inspiration and wealth of data he had gathered during his years aboard the Alfred Russel Wallace was a school teacher and naturalist who gave up teaching the anatomist Richard Owen, who had worked on many of to earn his living as a professional collector of exotic and animals from beagle, darwin took many years to formulate his theory and ready it for publication – Darwin’s vertebrate specimens and, in 1842, had “invented” the tropics. He collected extensively in South America, and from 1854 in the so long, in fact, that he was almost beaten to publication. nevertheless, when it as a separate category of . islands of . From these experiences, Wallace realized By 1842, Darwin’s evolutionary ideas were sufficiently emerged, darwin’s work had a profound effect. that species exist in variant advanced for him to produce a 35-page sketch and, by forms and that changes in 1844, a 250-page synthesis, a copy of which he sent in 1847 the environment could lead During a long life, Charles After his five-year round the world voyage, Darwin arrived Darwin saw himself largely as a , and published to the botanist, . This trusted friend to the loss of any ill-adapted Darwin wrote numerous back at the family home in Shrewsbury on 5 October 1836. books on coral reefs, volcanic islands, and geological was sympathetic to his approach and was one of the first variants with the continuing scientific papers, monographs, The following year he moved to London, dispersed his observations on South America. converts to ‘Darwinian ’. By the 1850s, success and survival of those that were and some seven books. Apart collections to appropriate experts, and, in 1838, was Darwin’s following was extended to include the dynamic adapted. In other words, he had independently come to from The Origin of Species, appointed Secretary to the Geological Society of London, DEVELOPINGTHEIDEA young zoologist (1825–95). the same conclusions as Darwin over a key aspect of the these included such topics as one of the most dynamic scientific societies of the day. He Meanwhile, however, Darwin was also developing his own Meanwhile, the results of an 8-year study of barnacles, both theory of evolution. Early in 1858 Wallace sent his paper to the biology of coral reefs and published the first edition of his Journal of researches, ideas through a series of notebooks on species transmutation, living and fossil, were published between 1851 and 1854, the ancestry of human beings the Linnean Society in London, and it was published under biological evolution, and the implication of such ideas for (above). married his cousin Emma Wedgwood in January 1839, and establishing Darwin’s credentials as a very able zoologist. the title “On the tendency of species to form varieties: and later in the year their first child was born. The young mankind. In 1839 he wrote to Henslow, his Cambridge This research helped him develop the principle of on the perpetuation of varieties and species by natural naturalist was quickly transformed into an established mentor, “I keep on steadily collecting every sort of fact, divergence in speciation, which is most active with intense selection”, alongside an extract from Darwin’s manuscript family man and junior member of a London elite that led which may throw light on the origin & variation of species”. competition for limited resources. In other words, Darwin on evolution and part of a letter sent by Darwin to the the world in newly developing academic sciences such as He also began to receive important information about his recognized that competition is a constant presence in American botanist in 1857 outlining his ideas. , zoology, and botany. Between 1842 and 1846 specimens from experts such as the ornithologist John nature and, as there is always some variation in populations, the result is natural selection of those adaptations that best fit the circumstances. Geographical isolation was just scientific community, the emergence of Wallace as a Because of his ideas about the one of several possible conditions for speciation, with competitor in the field of evolutionary theory shocked descent of man, Darwin was ecological pressures being equally if not more important. Darwin into action. In July 1858 he set to work on a book- frequently caricatured as a length ‘abstract’ of his ideas, in preference to the longer monkey – as in this 19th- century French cartoon where UNEXPECTED COMPETITION work that he had planned. By May 1859 he was working on he is seen leaping through In 1855, Darwin read with interest a theoretical paper by proofs, and on 24 November the 500-page The Origin of hoops of credulity, superstition, Alfred Russel Wallace, a young naturalist working in south Species by Means of Natural Selection, or the Preservation and ignorance. Philosopher and east Asia, who argued that new species tend to arise in of Favoured Races in the Struggle for Life was published. physician Émile Littré areas already occupied by a related species. By this time All 1250 copies of the initial print run sold on the first day. (1801–81), a well-known French Darwin’s friends were encouraging him to publish his Darwin had been forewarned about the hostile reception supporter of Darwin’s theory before someone else came up with a similar one, his book would receive by the criticism that had been supposedly “irreligious” ideas, and by spring of 1858 he had completed ten chapters of a heaped on the evolutionary ideas contained in Vestiges of holds the hoops (opposite). projected two-volume work entitled Natural Selection. In the of Creation, an anonymous work June 1858, however, Darwin received a bombshell with the published in 1844. He deliberately avoided discussing the Thomas Henry Huxley’s arrival of a new manuscript from Wallace, outlining his sensitive topic of human evolution, save only to predict vehement support for the theory that continuance of certain varieties of species that “Light will be thrown on the origin of man and his Darwin–Wallace theory of evolution through his writing might be perpetuated by processes of natural selection. history”. However, since he also concluded that ‘all organic and popular lectures helped the To Darwin’s dismay Wallace had independently come beings which have ever have lived on this earth have idea to gain more general up with a key aspect of his evolutionary theory. descended from some one primordial form, into which life acceptance and earned him the Luckily, Darwin’s network of scientific friends arranged a was first breathed’, his readers could easily draw their own nickname of “Darwin’s bulldog” compromise co-publication by the Linnean Society, conclusions. It was not until 1871, when the initial battles (above). ensuring that Darwin’s independent and earlier had largely been fought and won, that Darwin outlined his formulation of the idea was recognized. Although the detailed views on human origins and the importance of Linnean Society papers were largely ignored by the sexual competition in all evolutionary stories.

20 21 EVOLUTION THEPATTERNOFLIFE

cellular material are complex organic molecules that can be more familiar organisms, from single-celled amoebae to THE PATTERN OF LIFE distinguished from inorganic molecules. These are preserved multicellular plants, animals, and fungi. as particles of graphitic carbon within metamorphosed Today, Darwin’s problem with the incompleteness of shales from Greenland, over 3.7 billion years old . the fossil record has been largely resolved with the darwin developed his ideas about evolution based almost entirely on the study of living discovery of many extinct fossil groups. These amply species – at the time, the study of life’s long history and the fossil record was in its infancy, BRIDGINGTHEGAPS demonstrate many major evolutionary innovations such as and it was some time before the ultimately proved his theory right. Modern genetic analyses of the simplest known living the development of the limb with the transition organisms show that life can be separated into three major from aquatic to land-living , the appearance domains. The Bacteria are the most ancient and primitive, of feathers and wings in dinosaurs and their flying followed by the Archea from which the Eukaryota evolved descendants the , and the evolution of upright bipedal Amino acids are the building By the mid-19th century, when Darwin was developing his Noah’s Flood), although he had also discovered and named less than 2 billion years ago. The eukaryotes include all the walking in our own primate ancestors. blocks of proteins that are, in theory of evolution, it was clear that there was some pattern the first fossil primates from Cenozoic strata in . Darwin’s evolutionary turn, the essential ingredients to the distribution of fossils throughout the rock record. Consequently, it was still possible to claim that humanity fungi viruses monerans, etc protista expectations that fossils of of organic life (above). The earliest fossiliferous strata were in age, and was the result of some act of special creation by a deity. 89,000 1,000 4,800 30,000 primitive organisms would dominated by sea-living , including extinct However, by the mid-19th century there was mounting other animals eventually be found in groups such as trilobites and graptolites. The archaeological and fossil evidence that human-like 116,000 strata were not first fish and land plants appeared in the remains occurred alongside those of the extinct animals of algae confirmed until the 1950s, when , and reptiles and amphibians arrived the . By 1868, the first extinct human-related 27,000 microbial fossils were found in 43,000 in the “coal measures” – remains species – Homo neanderthalensis – was named, but it was 2-billion-year-old chert from of the first extensive forests. not for another 20 or so years that the fossil antiquity of Canada’s Lake Superior (above). vascular The Era was seen as the Age of humans and the growing evidence for human evolution plants Reptiles, following the discovery of extinct was generally accepted by the academic community. 248,400 marine forms such as the and plesiosaurs, the flying pterosaurs, and finally MISSINGLINKS ARTHROPODS the dinosaurs, which were not recognized as an Darwin was well aware of the nature of the fossil record in non hexapod arthropods independent fossil group until 1842. By this time, it was the first half of the 19th century. His theory of evolution The idea that all life, no matter 123,000 also known that primitive had been around in required that there should be fossil evidence for ancestral how complex, has descended from microscopic single-celled times, and by the 1860s birds were known to have forms shared by descendent groups, because ultimately all ARTHROPODS microbes that live in the sea first appeared in the Late Jurassic. The one group that did life has diverged and descended from a common ancestor. hexapod was revolutionary and not seem to turn up in the fossil record were humans. But he knew only too well that such common ancestral (insects) 925,000 disturbing for many In the 1820s the eminent French anatomist Georges forms for major groups had not been found, and he blamed Victorian minds (above). Cuvier had debunked earlier claims regarding the their absence primarily on the incompleteness of the rock existence of human remains (thought to be victims of and fossil record. His other major problem was the lack of fossils from As this chart of known present- Museums built to house the day species demonstrates Precambrian strata. Since several different wealth of new discoveries were (left), much of life’s variety is groups, such as brachiopods and trilobites, appeared in conceived as “cathedrals”, concentrated in a few groups of early Cambrian strata, they must have had ancestors that where the public could worship organisms – notably arthropods the newly emerging “gods” of lived in Precambrian times. Darwin admitted that their and vascular plants. However, science and technology (right). absence was a problem for his theory, but predicted that when more is known about the Precambrian fossils would turn up eventually, He was total diversity of life today, it is right, though it was not until the 1950s that the first possible that microbial convincing evidence of Precambrian life was found in organisms will outnumber even Russia and Canada. Since then, the record has been these groups. While life in the past probably followed a similar extended back to at least 3500 million (3.5 billion) years pattern, the fossil record is ago, providing indications that the sudden diversity of heavily skewed in other Cambrian life is more apparent than real. directions – towards organisms Among the most ancient remains of life are chemical with preservable hard parts, fossils, so called because all that remains of the original such as shelled molluscs.

24 25 EVOLUTION THEVARIETYOFFOSSILS

preserved in amber can survive for much longer, but while AMOUSECADAVER THE VARIETY OF FOSSILS organisms trapped in this ancient tree resin may seem perfectly preserved, appearances are deceptive. During the 1990s, attempts were made to recover DNA from amber while the traditional image of a fossil may be that of an ancient bone or tooth turned to stone, insects, but claims of success were unfounded and did not the true diversity of fossils is far greater, since a fossil can be any trace left by former life pass the critical scientific test of consistently reproducible and somehow preserved – this includes a variety of different means of preservation, and also results. However, other proteins have been recovered from fossil remains, most recently collagen from the 68-million- extends to traces of the way animals interacted with their environments. Decomposition after 3 days year-old bones of a Tyrannosaurus rex . Our everyday experience of terrestrial environments The long history of the Fossils provide the main evidence for the history and tissues. This fossilized skin and muscle is usually shows why it is difficult to preserve any remains of land- interdependence between evolution of life on Earth. But this simple statement hides preserved in ancient sediment when it has been replaced living animals or plants. Our landscapes are full of insects and plants is revealed a more complex reality that has taken centuries to resolve. by inorganic minerals, such as the apatite (a phosphate) or and life, but what happens when they die? How often by this bee, preserved complete Essentially, fossils are the toughest and least destructible pyrite (an iron sulphide). do we come across the bones of a , or even leaves with orchid in 15- to 20- parts of organisms, although occasionally more delicate Trace fossils are the marks left by a living organism on buried in soil? Deciduous plant leaves may cover the Decomposition after 5 days million-year-old amber structures and tissues are preserved, such as when an or within the sediment substrate – for example footprints, ground in autumn, but over weeks and months they are from the Dominican Republic entire body is freeze-dried in frozen ground. burrows and tooth or cutmarks. Most common are the degraded by fungi or bacterial decay and a variety of (above). Fossils vary in composition from mineralized bones burrows, and root traces of organisms that live or grow animals from snails to myriapods and . The and shells, to organic molecules preserved as blobs of within sediment. Rarely is the maker of the trace bones may survive for a year or so, but acids in the soil and bitumen, and the compressed, carbonized plant remains preserved, but trace fossils provide very important oxidation of the organic matrix soon weaken them – only that we know as coal. However, they can generally be evidence of certain environments such as tidal sandflats, teeth, with their tough dentine and enamel, last longer. These trilobite arthropods, perhaps buried alive while breeding in Decomposition after 7 days Some biological structures do survive well in soil – separated into just a few different kinds. and can prove the existence of ancient behaviours such as shallow water, were preserved by internal sediment moulds even as The cadaver of “Otzi”, a Chemical fossils are residual organic chemicals, such herding among certain plant-eating dinosaurs and the their mineralized exoskeletons dissolved away (above). tough coated spores, seeds, and pollen that are adapted for Neolithic hunter, found freeze- as the bituminous biomolecules recovered from Archean meat preparation techniques of Neanderthal hunters. survival in such conditions. Indeed, such structures may dried in a glacier in the Tyrolean strata more than three billion years old. Generally, their As we have seen, fossils preserved in the rock record among soft-bodied organisms that range from viruses and last long enough to be fossilized. Preservation of the soil Alps, preserves not only soft true organic nature and chemical composition can only be are usually the most robust parts of an organism, especially bacteria to giant squid. and other surface sediments requires special conditions tissues, but also DNA. However, resolved by sophisticated analytical equipment. mineralized skeletal materials such as shell, bones, and The bulk of body tissue in most organisms is composed such as rapid burial instead of the normal processes of the long-term survival of such Body fossils, the remains of original tissues, are the the tough woody tissues of plants, which can survive long of water and organic compounds that degrade rapidly surface weathering, and erosion. “protofossils” depends on the Decomposition after 9 days following death. This organic matter also represents persistence of permafrost, most common fossils, represented by countless shells and after death of an organism. As a result, the fossil record is which is much more ephemeral bones, and their impressions left in the rock. Some have heavily biased towards organisms that have such tissues, potential food for other organisms. In most natural FLUKES OF PRESERVATION than rock (below). been chemically altered, and a rare few preserve soft and does not fully represent the diversity of life, especially environments any dead body is scavenged, consumed, and So how is it that any fossil record of terrestrial life biologically degraded to some degree, leaving just the hard survives? And how come there are significant global parts as potential fossils. Occasionally, however, a body reserves of terrestrial deposits such as coal, the may come to rest in a naturally preservative medium or compressed remains of ancient tropical forests, swamps, location before it has deteriorated to any great extent. and bogs? The answer to both questions is that a Decomposition after 15 days Fortunately for paleontologists there are many excellent combination of geological conditions has made it possible. media and circumstances under which soft tissues can and Deposition of sediments and their organic remains in a have been preserved. These range from freeze-drying in generally subsiding landscape has buried them to such a subzero temperatures to soaking in oil, salt, or resin. depth that they survive subsequent erosion. However, the bulk of the fossil record consists of the HOWAREFOSSILSPRESERVED? shells and bones of marine organisms that lived in shallow Decomposition after 23 days While it is true that an entire or human can be seas on the continental margins, and within their waters.

freeze-dried in glacial sediments with their soft tissues and Yet even ocean-floor sediments and their organic remains This sequence of photos even some DNA preserved, such events are exceedingly are ultimately destroyed by another inexorable geological shows how processes of rare. Frozen and humans such as the 5200- process – subduction as a result of tectonic movements. decomposition and scaveng- year-old Tyrolean Ice-man “Otzi” are not, strictly speaking, More than 99.9 per cent of all the life that has existed ing rapidly destroy organic remains in most conditions. true fossils, since their enclosing icy sediments are is extinct, but fossils can give us some idea of what life was themselves ephemeral on a geological timescale. Fossils like in the past, and how it evolved.

28 29 EVOLUTION RECONSTRUCTINGTHEPAST

Catastrophic events such as the RECONSTRUCTING THE PAST eruption of Vesuvius in AD79 preserve some of the most complete records of past life – in to understand the processes of evolution, we must look at plants and animals even if they show the victims’ within their wider context – the environment in which they existed, the food sources dying moments (far left).

that were available to them, and the competitors and threats they faced. piecing Delicate tissues such as those together a complete picture of such ancient ecosystems calls for a variety of techniques. of angiosperm flowers are normally lost to the fossil record. Rare preservations, such Millimetre-sized shells of Today we take for granted scenes of the deep past understanding of comparative anatomy. However, a few as this 34-million-year-old single-celled organisms, such populated with dinosaurs and other extinct fossil animals spectacular new finds of soft tissue preservation, dating Florissantia, from as this foraminiferan, are and plants. And, with the use of computer graphics, such back as far as Cambrian times, do provide some accurate deposits in Colorado, USA, abundant in the fossil record. images are getting more and more superficially realistic. information about body shapes. require special conditions in fine-grained sediments (left). They can be used as proxy However, they often use modern land and seascapes for Over the last 200 years, enormous progress has been measures of past climates, the background and even modern plants that are not made in our understanding of the life of the geological of some past environments and the inter-relationships of engulfed the Roman town in AD79, preserving much of the since the shells record ocean usually appropriate. In this book we rely on the more past. Most, but by no means all, fossil organisms can now the various organisms that lived in them. Most fossil structure, artefacts, and some of the inhabitants. water chemistry at the time traditional art techniques that give a greater degree of be reconstructed with some degree of certainty as to their environments are waterlain, although in certain Volcanic eruptions, avalanches of sediment, dust- they were built (above). flexibility, detail, and accuracy. general appearance. The main exceptions are the plants circumstances low-lying terrestrial environments may be storms, and floods are common catastrophic events in the Even so, all such reconstructions are to some degree and some of the larger vertebrates, because their entire preserved, but uplands are exceedingly rare. And there are natural world, both on land and in water. They can imaginative fictions, since there are no visual records body form is so rarely preserved in the sedimentary rock still many problems of temporal resolution that make it overwhelm living communities and potentially preserve beyond the 30,000-year-old artworks made by early record. Plants are especially difficult because their impossible to determine whether the organisms actually much of their life. And, if the post-mortem environment modern humans who saw and depicted extinct animals numerous anatomical parts, such as pollen, leaves, woody lived together, died together, or simply had their remains lacks oxygen – for example the fine sediments of a lake Rock art, such as these such as the , woolly rhinoceros, and giant tissues, and roots, tend to be separated one from another jumbled together long after their death. bottom, they may even preserve some soft tissues. engravings from North Africa, . Beyond this in time, we know little of the coloration both during life and following death, and may be deposited As will be seen from the reconstructions in this book, records an abundance and of extinct animals and plants apart from some indications widely in different sedimentary environments. PIECINGTOGETHERTHEEVIDENCE most marine fossil locations were in shallow waters and diversity of life forms that are not of camouflage patterning. Detailed body shapes can Fortunately, interpretation of the rock record and the To understand all these factors, scientists have made lagoons, and most of the terrestrial locations were in lake now present because of climate be equally problematic, except through indirect associations of fossils from specific sites and stratigraphic detailed studies of the ecological relationships between and river deposits, so the actual land environments change and aided by inference and reconstruction of soft tissues, using our levels is now sophisticated enough to allow reconstruction living organisms and their environments. Over the 170 are largely reconstructed from indirect information human hunting (below). years since the first reconstructions of ancient scenes were preserved in waterlain attempted, we have learned a great deal about how death sediments and occurs in the natural world, what happens to the remains surrounding rocks. of plants and animals following death, how remains may be lost or recruited to the rock record, and what happens to them after burial, during the often complicated and destructive processes of fossilization. There are a few situations that tend to preserve organic remains William Buckland (1784–1856), particularly well. For body form and soft (above), was one of the first tissue preservation rapid entombment people to attempt the in a mummifying medium, such as cold dry air, reconstruction of life in the past – ice, amber resin, or salt is necessary, but these in this case an Ice Age are relatively rare in the geological record. den discovered in Yorkshire in Catastrophic and near-instantaneous natural 1821. His conclusions inspired burial processes can entomb a whole range his friend William Conybeare’s cartoon (right) showing Buckland of organisms that lived and died together. himself entering the cave. Such circumstances are known as “” scenarios, after the pyroclastic erupion that 30 ARCHEAN PROTEROZOIC

4650 MILLIONS OF YEARS 2500 542 Climate: widespread glaciation 647–635 million years ago SNOWBALL EARTH Biota: low-diversity marine micro-organisms (eg acritarchs) FLINDERS RANGE, SOUTH AUSTRALIA Common organisms: cold-tolerant micro-organisms Cryogenian Period of the Neoproterozoic Era

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One of the most extraordinary phenomena in 710, 640, and perhaps 580ma – known as the ᕡ dropstone Latitude then: c.8°N Earth’s early history is that of repeated and Sturtian, Marinoan, and Varangian glaciations. Latitude now: 31°S extensive glaciation. According to the Supposedly, the impact on environment and • Flinders Range mM Sea level: falling until end of “Snowball Earth” theory, at least two, and life was such that, in this frozen “icehouse” DROPSTONE (1) This metre-wide boulder – glaciation, then rising rapidly one of many found ‘floating’, surrounded by finer perhaps four or more, glacial phases state, ocean productivity and the weathering grained sediment – is a dropstone, formed when a Original environment: global terrestrial ice sheets and sea- encompassed the Precambrian world from pole of the land were shut down. Unable to melting iceberg released it to fall into soft sediment on the sea floor. No other natural mechanism can ice perhaps as far as the equator P Earth c.640ma to pole. Theoretically, growing polar ice sheets photosynthesize, marine phytoplankton died carry such large and heavy rocks out to sea, so the Deposits: “Elatina formation” reflected so much solar energy back into space off and the oceans became anoxic. Biological presence of dropstones is a useful indicator of glacial deposits that even the tropics were cooled sufficiently activity only revived in brief, hot interglacials. glacial activity. This spectacular specimen occurs Status: numerous accessible to ice over, with temperatures plummeting to Such stop–start, “freeze–fry” processes were within the Late-Proterozoic (Sturtian) glacial exposures of Elatina strata occur Flinders Range • -50°C, freezing the world’s oceans. precursors to the subsequent explosion of strata of Namibia’s Skeleton Coast, close to around Adelaide, South Australia The first glacial event occurred around 2.3 Ediacaran life, and may be responsible in some Narachaamspos. Carbonate rocks in the overlying Preservation: the glacial deposits strata lack dropstones: they show that, following are devoid of fossils P Fossil site today billion years ago, but the best known events way for that event. At least, that is the theory, the glacial event, the environment quickly are all late Proterozoic, dating to around but it is still far from proven. returned to its normal hot subtropical phase. 40 41 CAMBRIAN DEVONIAN CARBONIFEROUS

542 MILLIONS OF YEARS 488.3 443.7 416 359.2 299 251

SEA SCORPIONS AND JAWLESS FISH 430 million years ago Climate: warm-water tropical marine LESMAHAGOW, Stage of the Llandovery Common organisms: agnathans, eurypterids, phyllocarids, brachiopods, sponges, sea lilies, trilobites, nautiloids Biota: euryhaline shallow sea dwellers

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By Silurian times the agnathan fish were However, the agnathans were, by this time, p 1 ᕡ Ainiktozoon AINIKTOZOON ( ) This Latitude then: 17°S flourishing in the oceans of the world and facing fierce competition from both the newly strange thylacocephalan ᕢ Loganellia Latitude now: 56°N arthropod, about 15cm (6in) extending their range into shallow waters with evolving jawed fish, and large and active ᕣ Ceratiocaris long, had large compound Sea level: high fluctuating salinities. At least 15 different kinds arthropod predators – the eurypterids, some of ᕤ Pterygotus eyes for spotting its prey, Original environment: • Lesmahagow of agnathans are known from Silurian strata in which grew up to 2m (6.6ft) long. Also known ᕥ Jamoytius which it then captured with shallow marine to brackish waters Scotland’s Midland Valley, where they range as the sea scorpions, these extinct arthropods ᕦ Birkenia its grasping clawed Deposits: mud carbonates appendages. P from sluggish bottom-dwelling and heavily were armed with large and powerful pincers for Status: several protected historic Earth c.430ma armoured forms to more active non-armoured grabbing and pulling apart their prey. sites throughout the Midland Valley P LOGANELLIA (2) This m CERATIOCARIS (3) P BIRKENIA (6) of Scotland swimmers (such as Loganellia, Jamoytius and Numerous smaller arthropods are also • Lesmahagow thelodont agnathan, 15cm This free-swimming Here flattened on it side, Preservation: fossils flattened but Birkenia) that probably fed on a variety of found, including Ainiktozoon, once thought to (6in) long, has small paired shrimp-like arthropod, up the 10cm (4in) Birkenia mostly well preserved with some microbial and planktonic food. Some of the be a peculiar animal. Turned upside fins and a body covered in to 12cm (5in) long, had a shows numerous thin body fossilized soft tissues best specimens of these later swimmers have down, it was more easily recognized as a free- naked skin with some very bivalve carapace for scales. The mouth is to small scales. They are protection. The muscular the left with a large eye P Fossil site today been found in the fine-grained sediments of swimming, predatory thylacocephalan widely found across the tail could produce a rapid above, and the tail to localities such as Lesmahagow. arthropod, with a protective carapace. Baltic and . flick to escape predators. the right. 64 65 CAMBRIAN ORDOVICIAN SILURIAN DEVONIAN CARBONIFEROUS PERMIAN

542 MILLIONS OF YEARS 488.3 443.7 416 359.2 299 251

GREENING THE LAND 419 million years ago Climate: tropical, with global ‘greenhouse’ temperatures LUDFORD LANE, SHROPSHIRE, ENGLAND Ludfordian Stage of the Ludlow Epoch Common organisms: Cooksonia, Steganotheca, trigonotarbids, myriapods Biota: first land plants and animals

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The first land plants were primitive mosses and Steganotheca come from Late Silurian strata in M 2 ᕡ Lingula COOKSONIA ( ) Latitude then: 15°S lichens (bryophytes) that evolved in the Late the Welsh Borders. They had short (4cm/1.6in) Chemically isolated ᕢ Cooksonia Latitude now: 52°N Ordovician but were very restricted in their forked stems ending in spore-bearing capsules. from the rock, this ᕣ Steganotheca specimen of Sea level: high growth. Life on land in a relatively dry With no leaves, the stomata (cell openings for ᕤ Palaeotarbus Cooksonia shows the Original environment: • Ludford Lane atmosphere is difficult for all organisms. In “breathing”) were on stems and branches. cap-shaped reproductive coastal mudflats ᕥ Eoarthropleura structures that bore the colonizing the land, plants had the advantage The first animals on land were arthropods, ᕦ Strophochonetes Deposits: mud and sand plant’s spores. Some of the P of securing their energy from sunlight through pre-adapted for life in the inhospitable Status: many protected historic Earth c.419ma spores are still preserved sites scattered over the Welsh photosynthesis, while animals were dependent conditions by their tough, waterproof within the cup, and these Borders on either plants or other animals for food. exoskeletal armour. They included myriapod proved for the first time the P STEGANOTHECA (3) P PALAEOTARBUS (4) Preservation: fossils are generally However, plant tissue still needed support to “detritivores” that ate plant material already M COOKSONIA (2) A highly connection between the This primitive land plant These tiny (2–3mm/1in flattened but often well preserved • Ludford Lane grow against gravity, and for protection from degraded by soil bacteria, and carnivorous flattened and carbonized fossil parent plant and a offers an example of more long), air-breathing and particular (trilete) spore in fine-grained strata oxidation, hydration, and the damaging effect trigonotarbid arachnids. All these early shows the simple forked complex, first- and second- land-living arthropod branches and terminal structure. order branching. predators had paired P of ultraviolet light. Fossils of early vascular terrestrial fossils are found as river-borne Fossil site today reproductive structures of this Steganotheca grew to fangs with which to stab upright land plants, such as Cooksonia and fragments stranded along shorelines. primitive land plant. around 4.5cm (1.8in) high. their prey. 68 69 JURASSIC

251 199.6 145.5 65.5 MARINE REPTILES DIVERSIFY 233 million years ago Climate: tropical–equatorial MONTE SAN GIORGIO, Stage of the Epoch Common organisms: ammonites and clams Biota: marine fish and reptiles

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An extraordinary window on the marine life of Here abundant fish and ammonoid cephalopods ᕡ Shastasaurus Latitude then: 15°N the tropical Tethys Ocean first opened in the were hunted by a variety of marine reptiles such ᕢ Mixosaurus Latitude now: 45.5°N Monte late 19th century, when remarkably well- as ichthyosaurs (eg Mixosaurus) and San Giorgio • ᕣ Sea level: +25m (82ft) preserved fossils were discovered in shales and (eg ). Specialist predators such as ᕤ Saurichthys Original environment: dolomitic limestones near Besano in the the placodonts (eg Paraplacodus) had large flat stratified basin with anoxic ᕥ Paraplacodus southern Alps during quarrying for bitumen. teeth for crushing shellfish. bottom waters ᕦ Eoprotrachyceras The outcrop of Middle Triassic strata The strata also contain the skeletons of Deposits: black bituminous shales P Earth c.233ma ᕧ Askeptosaurus straddles the Italian–Swiss border, and has reptiles such as the bizarre Tanystropheus, and laminated dolomitic limestones ᕨ Ceresiosaurus surrendered hundreds of complete marine which grew to 6m (20ft) long with a stiff, Status: quarrying has been ᕩ Birgeria necessary to excavate the skeletons over the last 150 years, along elongated neck twice the length of its body. fossiliferous strata Monte San Giorgio • with thousands of fish (including 30 ray-finned Such an animal must have been essentially Preservation: flattened but often P species), clams, and ammonoids. marine, but the related Macronemus was only P TANYSTROPHEUS (3) Three genera of archosauromorphs have been found CERESIOSAURUS (8) The most abundant reptiles at Monte San Giorgio were the entire skeletons with some at Monte San Giorgio, including the strange Tanystropheus with its extremely amphibious nothosaurs. They were probably fish feeders, and may have laid eggs on land. P All these animals lived in the quiet waters of 80cm (31.5in) long and may have spent more fossilized soft tissues Fossil site today long neck, produced by elongation of between 12 and 24 individual vertebrae, They include Ceresiosaurus (up to 3m/10ft long), Paranothosaurus, , and the tiny a marine embayment off the main Tethys Ocean. time on land. depending on the species. (up to 30cm/12in long), of which several hundred specimens have been found. 116 117 EVOLUTION SYNAPSIDA SYNAPSIDA the include all the living mammals and their extinct relatives extending back to the late carboniferous – groups that have in the past been given the misleading name of “-like GORGONOPSIA VARANOPSEIDAE DICYNODONTIA OPHIACODONTIDAE DINOCEPHALIA CYNODONTIA EDAPHOSAURIDAE THEROCEPHALIA See page 274 reptiles”. despite their range and diversity, these extinct forms are still relatively unknown outside the world of .

Cotylorhyncus brevirostris Archaeothyris Dicynodon Moschorhinus Dvinia The appearance of the synapsids was a major This is the most This group of heavily This large, diverse This short-lived This group of Evolving in late event in evolution, and can be One of two main As their name This group evolved This group of groups of early suggests, these in the late Carbon- specialized plant- advanced group of built animals, up to group of group of predominantly Permian times, the reconstructed through the fossil record of its synapsids, the small- to medium- iferous and died out eaters, up to 3m eupelycosaurs and 4m (13ft) long, were evolved in mid- evolved in the carnivorous therap- survived various stages. The group was originally defined caseasaurians are sized synapsids, in mid-Permian (10ft) in length, are includes the largest among the first and Permian times and middle Permian and sids (up to 3m/10ft the end-Permian of these “sail- most primitive radiated to become quickly rose to long) are similar to extinction and went by the presence of a lower temporal opening only known from which grew up to times. It includes among the earliest Permian times. 1.5m (5ft) long, a number of long- known herbivorous backed” lizards, therapsids, the most successful become top the gorgonopsians, through several behind the eye, which provided space for the They include two resemble varanid snouted forms up to . They bear Dimetrodon, which appearing at the terrestrial amniotes carnivores of the but survived in waves of origination passage of enlarged jaw muscles. This famiies – the (monitor) lizards 3m (10ft) long, and a superficial grew to 3.5m (12ft) beginning of the of the late Permian late Permian, up to Gondwana to the and extinction, large plant-eating with slender bodies the earliest known resemblance to the in length. Tooth late Permian, and Early Triassic, 4m (13ft) long. They Middle Triassic. becoming in turn was connected to improvements in caseids, which and long limbs. – the caseids, but differ differentiation is expanding to surviving in are characterized by Characterized by progressively more processing food through tooth specialization, grew up to The slender, lightly 50cm (20in) in details. The further developed, become the Australia until the a skull structure features of the skull mammal-like. which in turn required restructuring of the lower 4m (13ft) long, built skull with Archaeothyris, head was very with enlargement of commonest therap- Early Cretaceous. with powerful jaw and teeth, they are and the smaller large eyes, a long which was small in relation to a the upper canines sid group with both In size they ranged muscles and tooth closely related to jaw and its articulation. The snout region was carnivorous narrow snout, discovered in the bulky body, but the and first incisor, carnivorous and from a small dog to differentiation with the cynodonts. extended in the carnivorous forms, but took on a eothyridids, which and jaws with bole of a fossil jaw had powerful while in the lower herbivorous forms, a large ox. The well-developed very different shape in some of the plant-eaters, look superficially specialized sharp, lycopod tree, muscles and teeth jaw the second and disappearing body is barrel- incisors and different but are recurved teeth, was preserved by late adapted for incisor is enlarged. before the end of shaped, with strong enlarged canines. where the front teeth were lost and replaced with united by the adapted for hunting Carboniferous “coal cropping vegetation. The group evolved the Permian. They limbs, a short tail, ̇ THERIODONTIA a horny, -like beak for shearing through structure of the down small but measure” strata at Elongated neural late in the are defined by their and a powerful tough plant material. snout and nostrils. active prey. The Joggins in Nova spines supported a Carboniferous and teeth, shortened beaked skull. They were a varanopseids were Scotia. Its slender large dorsal “sail”. died out at the jaw and thickened Synapsids arose in equatorial regions in late successful group probably the most snout is armed with They evolved in late beginning of the skull bones. Carboniferous times, and were initially lizard-like in early Permian agile predators of sharply pointed Carboniferous times late Permian. in appearance. The Permian and Triassic saw the times, but by the the time. They teeth, one of which and became ̇ THERAPSIDA SAIL-BACKEDPELYCOSAURS middle of the evolved during the shows a developed extinct in the origination and rapid expansion of successively Despite being one of the best known groups, the period were late Carboniferous canine-like form. middle Permian. traditional “Order Pelycosauria” are not featured on this more advanced groups, many of which soon died challenged by the and died out in late The group includes cladogram, since it is a paraphyletic group containing out to be replaced by new forms. rapidly evolving Permian times. aquatic, semi- species that are now placed within several groups including therapsids. They aquatic, and fully Ophiacodontidae, Edaphosauridae, and Spenacodontidae. ultimately died out terrestrial animals. THERIODONTIA Some animals within each of these latter groups in the end-Permian independently evolved a strange dorsal “sail” or “fin” extinction. This group is characterized by a number of structure on their backs – a web of skin supported by skull features such as laterally flaring extreme elongations of the neural spines from the vertebrae. cheek bones, more specialized and mammal- Probably the best known of these “sail-backed” species are THERAPSIDA like teeth, and an enlarged jawbone with the carnivorous sphenacodontid Dimetrodon and the This grouping includes the biarmosuchians, improved surfaces for muscle attachment. herbivorous Edaphosaurus. The function of the sail structure SYNAPSIDA dinocephalians, , and theriodonts. The theriodonts include the gorgonopsians, has generated a great deal of argument, but the two most It is characterized by enlarged fenestrae (the therocephalians, cynodonts, and all their This very large group is characterized by several popular suggestions are that it may have been used in typical synapsid holes in the skull), further mammalian descendants. Apart from SYNAPSIDA ̈ features of the skull and teeth, such as the presence mating displays, or for heat-exchange (allowing sunlight to specialization of the teeth into incisors, cynodonts, the last theriodonts became extinct of a lower temporal opening and the development of warm the animal in cold conditions, and helping the animal Inostrancevia from the Permian of Russia is a canines, and molars, and a more upright posture. in the Early Triassic. member of the short-lived gorgonopsian group canine-like “caniniforms”. to cool down when hot). of synapsids.

273 EVOLUTION SPECIESLISTING

(together known as the Ponginae), and spread beyond this continent. One of HOMINOIDEA (APES) • LIPOTYPHLA the African apes – chimps and gorillas these African species, Homo sapiens, Hyopsodus 188–9 AMPHILEMURIDAE plus humans and their fossil relatives arose some 200,000 years ago to Miocene – Extant Pholidocercus 198–9 PHENACODONTIDAE (together known as the Homininae). become the most widespread and within Anthropoidea 188–9 Their divergence resulted from the successful. ERINACEIDAE (HEDGEHOGS) see also Hominidae adoption of different modes of “Tupaiodon” 206–7 locomotion – the orang-utan swings by The apes, also known as hominoids, Gymnurechinus 210–1 • DINOCERATA • PONGINAE its arms (“brachiation”) and climbs are a group that unites the gibbons UINTATHERIIDAE slowly, while the African great apes PONGIN SIVAPITHECINES (Family Hylobatidae) with the • CHIROPTERA () Uintatherium 190–1 mostly use all four limbs to climb in a Sivapithecus 212–13 Hominidae (chimps, gorillas, typical quadripedal manner, and orang-utans, humans, and their MICROCHIROPTERA humans are bipedal. ancestors). Although there are few 196–7 • ARTIODACTYLA • HOMININAE The earliest known hominids are surviving ape species, their 190–1 DICHOBUNOIDEA fossil forms such as the Miocene age UNDETERMINED GROUP distribution in Africa and southeast 198–9 Diacodexis 188–9 Kenyapithecus from eastern Africa and Sahelanthropus 214–15 Asia reflects a much wider diversity Brachipposideros (leaf-nosed ) 208–9 Messelobunodon 196–7 Hipposideros 238–9 central . There is a reasonable “AUSTRALOPITHECINES” and distribution in the past. record of fossil Ponginae in Asia from Unfortunately, the early ape fossil Australopithecus afarensis 216–17 ONYCHONYCTERIDAE • ARTIODACTYL SUIFORMS Miocene times onwards, but there is a Australopithecus africanus 218–19 record is sparse, obscuring many 190–1 big gap in the record of African details of their origins within the (PIGS) “PARANTHROPINES” Homininae until around 6 million haplorhine primates around 25 million Hippopotamodon 212–13 Paranthropus boisei 220–1 CETARTIODACTYLA years ago. At present, the earliest fossil years ago. The best known early fossil • Nyanzochoerus 214–15 Stenopterygius. This relatively small, slender- eaters (and subsequently grazing plant- hominin is Sahelanthropus, a small HOMININI representative of the group is the ARCTOCYONIDAE Sus scrofa 222–3 skulled from Holzmaden in Germany LAURASIATHERIA eaters once the grasses had evolved in ape-like creature from the late Homo habilis 220–1 Miocene Proconsul from Africa. By late had a form strongly resembling a modern dolphin, Chriacus 180–1 (LAURASIATHERIAN times). Two important Miocene that lies close to the Homo antecessor 222–3 Miocene times, the apes were and probably had a similar fish-eating lifestyle. MAMMALS) perissodactyl groups that became divergence of ape and human Homo erectus/ergaster 224–5 abundant and widely dispersed across Early Cretaceous – Extant extinct but left good fossil records are branches from their common ancestor. Homo sapiens 226–7, 230–1, 236–7, Africa, Asia, and Europe. They were ICHTHYOSAURIA the chalicotheres and brontotheres. Some 20 human-related species 240–1, 242–3, 244–5 mostly fruit-eating, chimp-sized, and Early Triassic – Late Cretaceous within Boreoeutheria The latter were rhino-like browsers have diverged over the last 6 million Homo neanderthalensis 228–9 tailless, with short snouts, forward- compare Euarchontoglires such as the North American Brontops, years in Africa, but few of them have Homo floresiensis 238–9 facing eyes, and highly domed . within Diapsida which stood more than 2m (6.6ft) high Extending back to Early Cretaceous compare , Archosauria, at the shoulder. The similar sized times, the first laurasiatherian , chalicotheres were strange animals mammals included the ancestors of with horse-like heads, long grasping living insectivores such as , The extinct ichthyosaurs or “fish forelimbs, and short back legs all hedgehogs, moles (lipotyphlans), and lizards” were a very successful group ending in three-hooved digits. bats (chiropterans). Among more of predatory marine reptiles Among the remaining advanced members is a large branch throughout much of the Mesozoic. laurasiatherians, the carnivorans are known as the ferungulates, whch Their dolphin-shaped bodies were characterized by a pair of enlarged includes the familiar cetartiodactyls streamlined for the pursuit of fast- carnassial cheek teeth that work (cattle, pigs, and whales), swimming prey, their tetrapod limbs together as effective shears, cutting the perissodactyls (horses, rhinoceroses, were adapted as seal-like paddles for flesh off their prey for rapid ingestion. and tapirs), carnivorans (dogs, cats, steering, and the main propulsion Additionally, the canine “eye” or “dog” weasels, seals, and bears), and the came from a muscular tail. teeth have developed into dagger-like bizarre and less familiar pholidotans Ichthyosaurs grew up to 15m (50ft) fangs, capable of puncturing tough (pangolins). long, and had projecting beak-like hide to help hold and kill their prey. The cetartiodactyls are further jaws armed with sharp teeth. Their The pinnipeds (seals, sealions, and subdivided into the even-toed large eyes suggest that they depended walruses) are an aquatic group of (artiodactyls) and, according upon sight for hunting. carnivorans that probably evolved to molecular analysis, the cetaceans. from a bear-like ancestor in the The former include the suiforms (pigs ICHTHYOSAURIA Oligocene, perhaps similar to • and hippos) and the selenodontids Enaliarctos from . MIXOSAURIDAE (cattle, deer, giraffes, antelopes, and Finally, molecular analysis has Mixosaurus 116–17 camels) – their link with the revealed close links between the cetatceans, which include whales, SHASTASAURIDAE carnivorans and the strange scaly- dolphins, and porpoises, might seem Shastasaurus 116–17 skinned, ant-eating, and toothless surprising but is now supported by pangolins. Although living pangolins ICHTHYOSAURIDAE fossil evidence. The artiodactyls seem are restricted to Africa and southeast Ichthyosaurus 128–9 to have originated in Eocene times Asia, they were once more widespread from rabbit-sized plant-eaters such as STENOPTERYGIIDAE throughout North America and Diacodexis. There is also fossil Stenopterygius 130–1 Europe. Eomanis is a wonderfully evidence that the cetaceans arose from Platypterigius 164–5 preserved pangolin found in the a land-living artiodactyls such as OPTHALMOSAURIDAE Eocene shales of Messel in Germany. from Pakistan. Aegirosaurus 140–1 Eocene times also saw the diversification of the perissodactyls, ̇ Orang-utan (Pongo sp.). Although these ̈ Flying fox (Pteropus sp.). Large “fruit bats” and hominid apes are generally solitary, offspring stay which have odd numbers of toes, to their smaller, insect-eating relatives show how the with their mothers until the age of six or seven. become the dominant browsing plant- Laurasiatheria have evolved enormous variety.

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