It isn’t easy to become a fossil. The fate of nearly all living organisms—over 99.9 per cent of them—is to compost down to nothingness. When your spark is gone, every molecule you own will be nibbled off you or sluiced away to be put to use in some other system. That’s just the way it is. Even if you make it into the small pool of organisms, the less than 0.1 per cent, that don’t get devoured, the chances of being fossilized are very small.
In order to become a fossil, several things must happen. First, you must die in the right place. Only about 15 per cent of rocks can preserve fossils, so it’s no good keeling over on a future site of granite. In practical terms the deceased must become buried in sediment where it can leave an impression, like a leaf in wet mud, or decompose without exposure to oxygen, permitting the molecules in its bones and hard parts (and very occasionally softer parts) to be replaced by dissolved minerals, creating a petrified copy of the original. Then, as the sediments in which the fossil lies are carelessly pressed and folded and pushed about by Earth’s processes, the fossil must somehow maintain an identifiable shape. Finally, but above all, after tens of millions or perhaps hundreds of millions of years hidden away, it must be found and recognized as something worth keeping.
Only about one bone in a billion, it is thought, ever becomes fossilized. If that is so, it means that the complete fossil legacy of all the Americans alive today—that’s 270 million people with 206 bones each—will only be about fifty bones, one-quarter of a complete skeleton. That’s not to say, of course, that any of these bones will ever actually be found. Bearing in mind that they can be buried anywhere within an area of slightly over 9.3 million square kilometres, little of which will ever be turned over, much less examined, it would be something of a miracle if they were. Fossils are in every sense vanishingly rare. Most of what has lived on Earth has left behind no record at all. It has been estimated that less than one species in ten thousand has made it into the fossil record. That in itself is a stunningly infinitesimal proportion. However, if you accept the common estimate that the Earth has produced thirty billion species of creature in its time, and Richard Leakey and Roger Lewin’s statement (in The Sixth Extinction) that there are 250,000 species of creature in the fossil record, that reduces the proportion to just one in 120,000. Either way, what we possess is the merest sampling of all the life that the Earth has spawned.
Moreover, the record we do have is hopelessly skewed. Most land animals, of course, don’t die in sediments. They drop in the open and are eaten or left to rot or weather down to nothing. The fossil record, consequently, is almost absurdly biased in favour of marine creatures. About 95 per cent of all the fossils we possess are of animals that once lived under water, mostly in shallow seas.
I mention all this to explain why on a grey day in February I went to the Natural History Museum in London to meet a cheerful, vaguely rumpled, very likeable palaeontologist named Richard Fortey.
Fortey knows an awful lot about an awful lot. He is the author of a wry, splendid book called Life: An Unauthorised Biography, which covers the whole pageant of animate creation. But his first love is a type of marine creature called trilobites, which once teemed in Ordovician seas but haven’t existed for a long time except in fossilized form. All trilobites shared a basic body plan of three parts, or lobes—head, tail, thorax—from which comes the name. Fortey found his first when he was a boy clambering over rocks at St David’s Bay in Wales. He was hooked for life.
A well-preserved trilobite, a creature that dominated the oceans for three hundred million years—double the reign of dinosaurs. (Credit 21.2)
He took me to a gallery of tall metal cupboards. Each cupboard was filled with shallow drawers, and each drawer was filled with stony trilobites—twenty thousand specimens in all.
“It seems like a big number,” he agreed, “but you have to remember that millions upon millions of trilobites lived for millions upon millions of years in ancient seas, so twenty thousand isn’t a huge number. And most of these are only partial specimens. Finding a complete trilobite fossil is still a big moment for a palaeontologist.”
Trilobites first appeared—fully formed, seemingly from nowhere—about 540 million years ago, near the start of the great outburst of complex life popularly known as the Cambrian explosion, and then vanished, along with a great deal else, in the great and still mysterious Permian extinction three million or so centuries later. As with all extinct creatures, there is a natural temptation to regard them as failures, but in fact they were among the most successful animals ever to live. They reigned for 300 million years—twice the span of dinosaurs, which were themselves among history’s great survivors. Humans, Fortey points out, have survived so far for one-half of 1 per cent as long.
With so much time at their disposal, the trilobites proliferated prodigiously. Most remained small, about the size of modern beetles, but some grew to be as big as platters. Altogether they formed at least five thousand genera and sixty thousand species—though more turn up all the time. Fortey had recently been at a conference in South America where he was approached by an academic from a small provincial university in Argentina. “She had a box that was full of interesting things—trilobites that had never been seen before in South America, or indeed anywhere, and a great deal else. She had no research facilities to study them and no funds to look for more. Huge parts of the world are still unexplored.”
“In terms of trilobites?”
“No, in terms of everything.”
Throughout the nineteenth century, trilobites were almost the only known forms of early complex life, and for that reason were assiduously collected and studied. The big mystery about them was their sudden appearance. Even now, as Fortey says, it can be startling to go to the right formation of rocks and to work your way upwards through the aeons, finding no visible life at all, and then suddenly “a whole Profallotaspis or Elenellus as big as a crab will pop into your waiting hands.” These were creatures with limbs, gills, nervous systems, probing antennae, “a brain of sorts,” in Fortey’s words, and the strangest eyes ever seen. Made of calcite rods, the same stuff that forms limestone, they constituted the earliest visual systems known. More than this, the earliest trilobites didn’t consist of just one venturesome species but dozens, and didn’t appear in one or two locations but all over. Many thinking people in the nineteenth century saw this as proof of God’s handiwork and refutation of Darwin’s evolutionary ideals. If evolution proceeded slowly, they asked, then how did he account for this sudden appearance of complex, fully formed creatures? The fact is, he couldn’t.
And so matters seemed destined to remain for ever until one day in 1909, three months shy of the fiftieth anniversary of the publication of Darwin’s On the Origin of Species, when a palaeontologist named Charles Doolittle Walcott made an extraordinary find in the Canadian Rockies.
Walcott was born in 1850 and grew up near Utica, New York, in a family of modest means, which became more modest still with the sudden death of his father when Charles was an infant. As a boy Walcott discovered that he had a knack for finding fossils, particularly trilobites, and built up a collection of sufficient distinction that it was bought by Louis Agassiz for his museum at Harvard for a small fortune—about £45,000 in today’s money Although he had barely a high-school education and was self-taught in the sciences, Walcott became a leading authority on trilobites and was the first person to establish that they were arthropods, the group that includes modern insects and crustaceans.
In 1879 Walcott took a job as a field researcher with the newly formed United States Geological Survey and served with such distinction that within fifteen years he had risen to be its head. In 1907 he was appointed secretary of the Smithsonian Institution, where he remained until his death in 1927. Despite his administrative obligations, he continued to do fieldwork and to write prolifically. “His books fill a library shelf,” according to Fortey. Not incidentally, he was also a founding director of the National Advisory Committee for Aeronautics, which eventually became the National Aeronautics and Space Agency, or NASA, and thus can rightly be considered the grandfather of the space age.
Charles Doolittle Walcott poses before his historic find. Walcott quarried tens of thousands of specimens from the Burgess Shale. (Credit 21.3)
But what he is remembered for now is an astute but lucky find in British Columbia, high above the little town of Field, in the late summer of 1909. The customary version of the story is that Walcott, accompanied by his wife, was riding on a mountain trail when his wife’s horse slipped on loose stones. Dismounting to assist her, Walcott discovered that the horse had turned a slab of shale that contained fossil crustaceans of an especially ancient and unusual type. Snow was falling—winter comes early to the Canadian Rockies—so they didn’t linger, but the next year at the first opportunity Walcott returned to the spot. Tracing the presumed route of the rocks’ slide, he climbed 750 feet to near the mountain’s summit. There, 8,000 feet above sea level, he found a shale outcrop, about the length of a city block, containing an unrivalled array of fossils from soon after the moment when complex life burst forth in dazzling profusion—the famous Cambrian explosion. Walcott had found, in effect, the holy grail of palaeontology. The outcrop became known as the Burgess Shale, from the name of the ridge on which it was found, and for a long time it provided “our sole vista upon the inception of modern life in all its fullness,” as the late Stephen Jay Gould recorded in his popular book Wonderful Life.
Gould, ever scrupulous, discovered from reading Walcott’s diaries that the story of the Burgess Shale’s discovery appears to have been somewhat embroidered—Walcott makes no mention of a slipping horse or falling snow—but there is no disputing that it was an extraordinary find.
Marrella, one of over a hundred species of a previously unknown type found by Walcott. (Credit 21.4)
It is almost impossible for us, whose time on Earth is limited to a breezy few decades, to appreciate how remote in time from us the Cambrian outburst was. If you could fly backwards into the past at the rate of one year per second, it would take you about half an hour to reach the time of Christ, and a little over three weeks to get back to the beginnings of human life. But it would take you twenty years to reach the dawn of the Cambrian period. It was, in other words, an extremely long time ago and the world was a very different place.
For one thing, 500 million years ago and more when the Burgess Shale was formed it wasn’t at the top of a mountain but at the foot of one. Specifically, it was in a shallow ocean basin at the bottom of a steep cliff. The seas of that time teemed with life, but normally the animals left no record because they were soft-bodied and decayed upon dying. At Burgess, however, the cliff collapsed and the creatures below, entombed in a mudslide, were pressed like flowers in a book, their features preserved in wondrous detail.
In annual summer trips from 1910 to 1925 (by which time he was seventy-five years old), Walcott excavated tens of thousands of specimens (Gould says eighty thousand; the normally unimpeachable fact checkers of National Geographic say sixty thousand), which he brought back to Washington for further study. In both sheer numbers and diversity the collection was unparalleled. Some of the Burgess fossils had shells; many others did not. Some of the creatures were sighted, others blind. The variety was enormous, consisting of 140 species, by one count. “The Burgess Shale included a range of disparity in anatomical designs never again equaled, and not matched today by all the creatures in the world’s oceans,” Gould wrote.
Unfortunately, according to Gould, Walcott failed to discern the significance of what he had found. “Snatching defeat from the jaws of victory,” Gould wrote in another work, Eight Little Piggies, “Walcott then proceeded to misinterpret these magnificent fossils in the deepest possible way.” He placed them into modern groups, making them ancestral to today’s worms, jellyfish and other creatures, and thus failed to appreciate their distinctness. “Under such an interpretation,” Gould sighed, “life began in primordial simplicity and moved inexorably, predictably onward to more and better.”
Walcott died in 1927 and the Burgess fossils were largely forgotten. For nearly half a century they stayed shut away in drawers in the National Museum of Natural History in Washington, seldom consulted and never questioned. Then in 1973 a graduate student from Cambridge University named Simon Conway Morris paid a visit to the collection. He was astonished by what he found. The fossils were far more varied and magnificent than Walcott had indicated in his writings. In taxonomy the category that describes the basic body plans of organisms is the phylum, and here, Conway Morris concluded, were drawer after drawer of such anatomical singularities—all amazingly and unaccountably unrecognized by the man who had found them.
With his supervisor, Harry Whittington, and fellow graduate student Derek Briggs, Conway Morris spent the next several years making a systematic revision of the entire collection, and cranking out one exciting monograph after another as discovery piled upon discovery. Many of the creatures employed body plans that were not simply unlike anything seen before or since, but were bizarrely different. One, Opabinia, had five eyes and a nozzle-like snout with claws on the end. Another, a disc-shaped being called Peytoia, looked almost comically like a circular pineapple slice. A third had evidently tottered about on rows of stilt-like legs, and was so odd that they named it Hallucigenia. There was so much unrecognized novelty in the collection that at one point upon opening a new drawer Conway Morris famously was heard to mutter, “Oh fuck, not another phylum.”
The English team’s revisions showed that the Cambrian had been a time of unparalleled innovation and experimentation in body designs. For almost four billion years life had dawdled along without any detectable ambitions in the direction of complexity, and then suddenly, in the space of just five or ten million years, it had created all the basic body designs still in use today. Name a creature, from a nematode worm to Cameron Diaz, and they all use architecture first created in the Cambrian party.
What was most surprising, however, was that there were so many body designs that had failed to make the cut, so to speak, and left no descendants. Altogether, according to Gould, at least fifteen and perhaps as many as twenty of the Burgess animals belonged to no recognized phylum. (The number soon grew in some popular accounts to as many as a hundred—far more than the Cambridge scientists ever actually claimed.) “The history of life,” wrote Gould, “is a story of massive removal followed by differentiation within a few surviving stocks, not the conventional tale of steadily increasing excellence, complexity, and diversity.” Evolutionary success, it appeared, was a lottery.
Hallucigenia, one of the many weird, and, as it turned out, exceedingly controversial, finds from Canada. (Credit 21.5)
One creature that did manage to slip through, a small wormlike being called Pikaia gracilens, was found to have a primitive spinal column, making it the earliest known ancestor of all later vertebrates, including us. Pikaia were by no means abundant among the Burgess fossils, so goodness knows how close they may have come to extinction. Gould, in a famous quotation, leaves no doubt that he sees our lineal success as a fortunate fluke: “Wind back the tape of life to the early days of the Burgess Shale; let it play again from an identical starting point, and the chance becomes vanishingly small that anything like human intelligence would grace the replay.”
Gould’s Wonderful Life was published in 1989 to general critical acclaim and was a great commercial success. What wasn’t generally known was that many scientists didn’t agree with Gould’s conclusions at all, and that it was all soon to get very ugly. In the context of the Cambrian, “explosion” would soon have more to do with modern tempers than ancient physiological facts. In fact, we now know, complex organisms existed at least a hundred million years before the Cambrian. We should have known a whole lot sooner. Nearly forty years after Walcott made his discovery in Canada, on the other side of the planet in Australia a young geologist named Reginald Sprigg found something even older and in its way just as remarkable.
In 1946 Sprigg, a young assistant government geologist for the state of South Australia, was sent to make a survey of abandoned mines in the Ediacaran Hills of the Flinders Range, an expanse of baking outback some 500 kilometres north of Adelaide. The idea was to see if there were any old mines that might be profitably reworked using newer technologies, so he wasn’t studying surface rocks at all, still less fossils. But one day, while eating his lunch, Sprigg idly overturned a hunk of sandstone and was surprised—to put it mildly—to see that the rock’s surface was covered in delicate fossils, rather like the impressions leaves make in mud. These rocks predated the Cambrian explosion. He was looking at the dawn of visible life.
Sprigg submitted a paper to Nature, but it was turned down. He read it instead at the next annual meeting of the Australian and New Zealand Association for the Advancement of Science, but it failed to find favour with the association’s head, who said the Ediacaran imprints were merely “fortuitous inorganic markings”—patterns made by wind or rain or tides, but not living beings. His hopes not yet entirely crushed, Sprigg travelled to London and presented his findings to the 1948 International Geological Congress, but failed to excite either interest or belief. Finally, for want of a better outlet, he published his findings in the Transactions of the Royal Society of South Australia. Then he quit his government job and took up oil exploration.
A cast of Mawsonite spriggi, a specimen of Ediacaran fauna from Australia, showing that complex body forms clearly predated the Cambrian period. (Credit 21.6)
Nine years later, in 1957, a schoolboy named Roger Mason, while walking through Charnwood Forest in the English Midlands, found a rock with a strange fossil in it, similar to a modern sea pen and exactly like some of the specimens Sprigg had found and been trying to tell everyone about ever since. The schoolboy handed it in to a palaeontologist at the University of Leicester, who identified it at once as Precambrian. Young Mason got his picture in the papers and was treated as a precocious hero; he still is in many books. The specimen was named in his honour Charnia masoni.
Today some of Sprigg’s original Ediacaran specimens, along with many of the other fifteen hundred that have been found throughout the Flinders Range since that time, can be seen in a glass case in an upstairs room of the stout and lovely South Australian Museum in Adelaide, but they don’t attract a great deal of attention. The delicately etched patterns are rather faint and not terribly arresting to the untrained eye. They are mostly small and disc-shaped, with occasional, vague trailing ribbons. Fortey has described them as “soft-bodied oddities.”
The South Australian geologist Reginald Sprigg, who in 1946 found relics of the earliest complex living organisms. His discovery was repeatedly dismissed by experts, and he eventually turned his back on geology in favour of oil exploration. (Credit 21.7)
There is still very little agreement about what these things were or how they lived. They had, as far as can be told, no mouth or anus with which to take in and discharge digestive materials, and no internal organs with which to process them along the way. “In life,” Fortey says, “most of them probably simply lay upon the surface of the sandy sediment, like soft, structureless and inanimate flatfish.” At their liveliest, they were no more complex than jellyfish. All the Ediacaran creatures were diploblastic, meaning they were built from two layers of tissue. With the exception of jellyfish, all animals today are triploblastic.
Some experts think they weren’t animals at all, but more like plants or fungi. The distinctions between plant and animal are not always clear even now. The modern sponge spends its life fixed to a single spot and has no eyes or brain or beating heart, and yet is an animal. “When we go back to the Precambrian the differences between plants and animals were probably even less clear,” says Fortey. “There isn’t any rule that says you have to be demonstrably one or the other.”
Nor is it agreed that the Ediacaran organisms are in any way ancestral to anything alive today (except possibly some jellyfish). Many authorities see them as a kind of failed experiment, a stab at complexity that didn’t take, possibly because the sluggish Ediacaran organisms were devoured or outcompeted by the lither and more sophisticated animals of the Cambrian period.
“There is nothing closely similar alive today,” Fortey has written. “They are difficult to interpret as any kind of ancestors of what was to follow.”
The feeling was that ultimately they weren’t terribly important to the development of life on Earth. Many authorities believe that there was a mass extermination at the Precambrian-Cambrian boundary and that all the Ediacaran creatures (except the uncertain jellyfish) failed to move on to the next phase. The real business of complex life, in other words, started with the Cambrian explosion. That’s how Gould saw it, in any case.
As for the revisions of the Burgess Shale fossils, almost at once people began to question the interpretations and, in particular, Gould’s interpretation of the interpretations. “From the first there were a number of scientists who doubted the account that Steve Gould had presented, however much they admired the manner of its delivery,” Fortey wrote in Life. That is putting it mildly.
“If only Stephen Gould could think as clearly as he writes!” barked the Oxford academic Richard Dawkins in the opening line of a review (in the Sunday Telegraph) of Wonderful Life. Dawkins acknowledged that the book was “unputdownable” and a “literary tour-de-force,” but accused Gould of engaging in a “grandiloquent and near-disingenuous” misrepresentation of the facts by suggesting that the Burgess revisions had stunned the palaeontological community. “The view that he is attacking—that evolution marches inexorably towards a pinnacle such as man—has not been believed for 50 years,” Dawkins fumed.
That was a subtlety lost on many general reviewers. One, writing in the New York Times Book Review, cheerfully suggested that as a result of Gould’s book scientists “have been throwing out some preconceptions that they had not examined for generations. They are, reluctantly or enthusiastically, accepting the idea that humans are as much an accident of nature as a product of orderly development.”
But the real heat directed at Gould arose from the belief that many of his conclusions were simply mistaken or carelessly inflated. Writing in the journal Evolution, Dawkins attacked Gould’s assertions that “evolution in the Cambrian was a different kind of process from today” and expressed exasperation at Gould’s repeated suggestions that “the Cambrian was a period of evolutionary ‘experiment,’ evolutionary ‘trial and error,’ evolutionary ‘false starts’…It was the fertile time when all the great ‘fundamental body plans’ were invented. Nowadays, evolution just tinkers with old body plans. Back in the Cambrian, new phyla and new classes arose. Nowadays we only get new species!”
The Harvard palaeontologist and born controversialist Stephen Jay Gould, whose popular interpretations of the Burgess Shale finds angered some in the scientific community. (Credit 21.8)
Noting how often this idea—that there are no new body plans—is picked up, Dawkins says: “It is as though a gardener looked at an oak tree and remarked, wonderingly: ‘Isn’t it strange that no major new boughs have appeared on this tree for many years? These days, all the new growth appears to be at the twig level.’”
“It was a strange time,” Fortey says now, “especially when you reflected that this was all about something that happened five hundred million years ago, but feelings really did run quite high. I joked in one of my books that I felt as if I ought to put a safety helmet on before writing about the Cambrian period, but it did actually feel a bit like that.”
Strangest of all was the response of one of the heroes of Wonderful Life, Simon Conway Morris, who startled many in the palaeontological community by rounding abruptly on Gould in a book of his own, The Crucible of Creation. “I have never encountered such spleen in a book by a professional,” Fortey wrote later. “The casual reader of The Crucible of Creation, unaware of the history, would never gather that the author’s views had once been close to (if not actually shared with) Gould’s.”
When I asked Fortey about it, he said: “Well, it was very strange, quite shocking really, because Gould’s portrayal of him had been so flattering. I could only assume that Simon was embarrassed. You know, science changes but books are permanent, and I suppose he regretted being so irremediably associated with views that he no longer altogether held. There was all that stuff about ‘Oh fuck, another phylum’ and I expect he regretted being famous for that. You’d never know from reading Simon’s book that his views had once been nearly identical to Gould’s.”
What happened was that the early Cambrian fossils began to undergo a period of critical reappraisal. Fortey and Derek Briggs—one of the other principals in Gould’s book—used a method known as cladistics to compare the various Burgess fossils. In simple terms, cladistics consists of organizing organisms on the basis of shared features. Fortey gives as an example the idea of comparing a shrew and an elephant. If you considered the elephant’s large size and striking trunk you might conclude that it could have little in common with a tiny, sniffling shrew. But if you compared both of them with a lizard, you would see that the elephant and shrew were in fact built to much the same plan. In essence, what Fortey is saying is that Gould saw elephants and shrews where he and Briggs saw mammals. The Burgess creatures, they believed, weren’t as strange and various as they appeared at first sight. “They were often no stranger than trilobites,” Fortey says now. “It is just that we have had a century or so to get used to trilobites. Familiarity, you know, breeds familiarity.”
This wasn’t, I should note, because of sloppiness or inattention. Interpreting the forms and relationships of ancient animals on the basis of often distorted and fragmentary evidence is clearly a tricky business. Edward O. Wilson has noted that if you took selected species of modern insects and presented them as Burgess-style fossils nobody would ever guess that they were all from the same phylum, so different are their body plans. Also instrumental in helping revisions were the discoveries of two further early Cambrian sites, one in Greenland and one in China, plus more scattered finds, which among them yielded many additional and often better specimens.
A fossilized Anomalocaris, the creature illustrated at the start of the chapter. Because so many of the Burgess Shale creatures were fragmented and distorted during fossilization, their interpretation was bound to be a matter of debate. (Credit 21.9)
The upshot is that the Burgess fossils were found to be not so different after all. Hallucigenia, it turned out, had been reconstructed upside down. Its stilt-like legs were actually spikes along its back. Peytoia, the weird creature that looked like a pineapple slice, was found to be not a distinct creature but merely part of a larger animal called Anomalocaris. Many of the Burgess specimens have now been assigned to living phyla—just where Walcott put them in the first place. Hallucigenia and some others are thought to be related to Onychophora a group of caterpillar-like animals. Others have been reclassified as precursors of the modern annelids. In fact, says Fortey, “there are relatively few Cambrian designs that are wholly novel. More often they turn out to be just interesting elaborations of well-established designs.” As he wrote in Life: “None was as strange as a present day barnacle, nor as grotesque as a queen termite.”
A sleeker, more cartoon-like view of Anomalocaris shows how much room for interpretation ancient fossils often give. (Credit 21.10)
So the Burgess Shale specimens weren’t so spectacular after all. This made them, as Fortey has written, “no less interesting, or odd, just more explicable.” Their weird body plans were just a kind of youthful exuberance—the evolutionary equivalent, as it were, of spiked hair and tongue studs. Eventually the forms settled into a staid and stable middle age.
But that still left the enduring question of where all these animals had come from—how they had suddenly appeared from nowhere.
Alas, it turns out the Cambrian explosion may not have been quite so explosive as all that. The Cambrian animals, it is now thought, were probably there all along, but were just too small to see. Once again it was trilobites that provided the clue—in particular, that seemingly mystifying appearance of different types of trilobite in widely scattered locations around the globe, all at more or less the same time.
On the face of it, the sudden appearance of lots of fully formed but varied creatures would seem to enhance the miraculousness of the Cambrian outburst, but in fact it did the opposite. It is one thing to have one well-formed creature like a trilobite burst forth in isolation—that really is a wonder—but to have many of them, all distinct but clearly related, turning up simultaneously in the fossil record in places as far apart as China and New York, clearly suggests that we are missing a big part of their history There could be no stronger evidence that they simply had to have a forebear—some grandfather species that started the line in a much earlier past.
And the reason we haven’t found these earlier species, it is now thought, is that they were too tiny to be preserved. Says Fortey: “It isn’t necessary to be big to be a perfectly functioning, complex organism. The sea swarms with tiny arthropods today that have left no fossil record.” He cites the little copepod, which numbers in the trillions in modern seas and clusters in shoals large enough to turn vast areas of the ocean black, and yet our total knowledge of its ancestry is a single specimen found in the body of an ancient fossilized fish.
“The Cambrian explosion, if that’s the word for it, probably was more an increase in size than a sudden appearance of new body types,” Fortey says. “And it could have happened quite swiftly, so in that sense I suppose it was an explosion.” The idea is that, just as mammals bided their time for a hundred million years until the dinosaurs cleared off and then seemingly burst forth in profusion all over the planet, so too perhaps the arthropods and other triploblasts waited in semi-microscopic anonymity for the dominant Ediacaran organisms to have their day. Says Fortey: “We know that mammals increased in size quite dramatically after the dinosaurs went—though when I say quite abruptly I of course mean it in a geological sense. We’re still talking millions of years.”
Incidentally, Reginald Sprigg did eventually get a measure of overdue credit. One of the main early genera, Spriggina, was named in his honour, as were several species, and the whole became known as the Ediacaran fauna after the hills through which he had searched. By this time, however, Sprigg’s fossil-hunting days were long over. After leaving geology he founded a successful oil company and eventually retired to an estate in his beloved Flinders Range where he created a wildlife reserve. He died in 1994 a rich man.
A tyrannosaurus expresses understandable alarm at the arrival of a lethal meteor in this irresistibly dramatic but misleading interpretation of the last instant before impact of the rock that wiped out the dinosaurs. Travelling faster than a bullet, an incoming meteor would be moving much too swiftly to be seen, much less to provoke alarm. (Credit 22.1)