Fortey knows an awful lot about an awful lot. He is the author of a wry, splendid bookcalled Life: An Unauthorised Biography, which covers the whole pageant of animate creation.
“If only Stephen Gould could think as clearly as he writes!” barked the Oxford academicRichard Dawkins in the opening line of a review (in the London Sunday Telegraph) ofWonderful Life. Dawkins acknowledged that the book was “unputdownable” and a “literarytour-de-force,” but accused Gould of engaging in a “grandiloquent and near-disingenuous”
For one thing, 500-million-plus years ago when the Burgess Shale was formed it wasn’t atthe top of a mountain but at the foot of one. Specifically it was a shallow ocean basin at thebottom of a steep cliff. The seas of that time teemed with life, but normally the animals left norecord because they were soft-bodied and decayed upon dying. But at Burgess the cliffcollapsed, and the creatures below, entombed in a mudslide, were pressed like flowers in abook, their features preserved in wondrous detail.
“It is as though a gardener looked at an oak tree and remarked, wonderingly: ‘Isn’t it strangethat no major new boughs have appeared on this tree for many years? These days, all the newgrowth appears to be at the twig level.’ ”
In fact, we now know, complex organisms existed at least a hundred million years beforethe Cambrian. We should have known a whole lot sooner. Nearly forty years after Walcottmade his discovery in Canada, on the other side of the planet in Australia, a young geologistnamed Reginald Sprigg found something even older and in its way just as remarkable.
With so much time at their disposal, the trilobites proliferated prodigiously. Most remainedsmall, about the size of modern beetles, but some grew to be as big as platters. Altogetherthey formed at least five thousand genera and sixty thousand species—though more turn upall the time. Fortey had recently been at a conference in South America where he wasapproached by an academic from a small provincial university in Argentina. “She had a boxthat was full of interesting things—trilobites that had never been seen before in SouthAmerica, or indeed anywhere, and a great deal else. She had no research facilities to studythem and no funds to look for more. Huge parts of the world are still unexplored.”
We’re still talking millions of years.”
But his first love is a type of marine creature called trilobites that once teemed in Ordovicianseas but haven’t existed for a long time except in fossilized form. All shared a basic body planof three parts, or lobes—head, tail, thorax—from which comes the name. Fortey found hisfirst when he was a boy clambering over rocks at St. David’s Bay in Wales. He was hookedfor life.
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 wasembarrassed. You know, science changes but books are permanent, and I suppose he regrettedbeing so irremediably associated with views that he no longer altogether held. There was allthat stuff about ‘oh fuck, another phylum’ and I expect he regretted being famous for that.”
But it would take you twenty years to reach the dawn of the Cambrian period. It was, in otherwords, an extremely long time ago, and the world was a very different place.
It is almost impossible for us whose time on Earth is limited to a breezy few decades toappreciate how remote in time from us the Cambrian outburst was. If you could fly backwardsinto the past at the rate of one year per second, it would take you about half an hour to reachthe time of Christ, and a little over three weeks to get back to the beginnings of human life.
“There is nothing closely similar alive today,” Fortey has written. “They are difficult tointerpret as any kind of ancestors of what was to follow.”
Sprigg submitted a paper to Nature , but it was turned down. He read it instead at the nextannual meeting of the Australian and New Zealand Association for the Advancement ofScience, but it failed to find favor with the association’s head, who said the Ediacaranimprints were merely “fortuitous inorganic markings”—patterns made by wind or rain ortides, but not living beings. His hopes not yet entirely crushed, Sprigg traveled to London andpresented his findings to the 1948 International Geological Congress, but failed to exciteeither interest or belief. Finally, for want of a better outlet, he published his findings in theTransactions of the Royal Society of South Australia. Then he quit his government job andtook up oil exploration.
It is one thing to have one well-formed creature like a trilobite burst forth in isolation—thatreally is a wonder—but to have many of them, all distinct but clearly related, turning upsimultaneously in the fossil record in places as far apart as China and New York clearlysuggests that we are missing a big part of their history. There could be no stronger evidencethat they simply had to have a forebear—some grandfather species that started the line in amuch earlier past.
So the Burgess Shale specimens weren’t so spectacular after all. This made them, as Forteyhas written, “no less interesting, or odd, just more explicable.” Their weird body plans werejust a kind of youthful exuberance—the evolutionary equivalent, as it were, of spiked hair andtongue studs. Eventually the forms settled into a staid and stable middle age.
Although he had barely a high school education and was self taught in the sciences, Walcottbecame a leading authority on trilobites and was the first person to establish that trilobiteswere arthropods, the group that includes modern insects and crustaceans.
“It seems like a big number,” he agreed, “but you have to remember that millions uponmillions of trilobites lived for millions upon millions of years in ancient seas, so twentythousand isn’t a huge number. And most of these are only partial specimens. Finding acomplete trilobite fossil is still a big moment for a paleontologist.”
One creature thatdid manage to slip through, a small wormlike being called Pikaiagracilens, was found to have a primitive spinal column, making it the earliest known ancestorof all later vertebrates, including us.Pikaia were by no means abundant among the Burgessfossils, so goodness knows how close they may have come to extinction. Gould, in a famousquotation, leaves no doubt that he sees our lineal success as a fortunate fluke: “Wind back thetape of life to the early days of the Burgess Shale; let it play again from an identical startingpoint, and the chance becomes vanishingly small that anything like human intelligence wouldgrace the replay.”
About 95 percent of all the fossils we possess are of animals that once lived under water,mostly in shallow seas.
misrepresentation of the facts by suggesting that the Burgess revisions had stunned thepaleontological community. “The view that he is attacking—that evolution marchesinexorably toward a pinnacle such as man—has not been believed for 50 years,” Dawkinsfumed.
Alas, it turns out the Cambrian explosion may not have been quite so explosive as all that.
Some experts think they weren’t animals at all, but more like plants or fungi. Thedistinctions between plant and animal are not always clear even now. The modern spongespends its life fixed to a single spot and has no eyes or brain or beating heart, and yet is ananimal. “When we go back to the Precambrian the differences between plants and animalswere probably even less clear,” says Fortey. “There isn’t any rule that says you have to bedemonstrably one or the other.”
On the face of it, the sudden appearance of lots of fully formed but varied creatures wouldseem to enhance the miraculousness of the Cambrian outburst, but in fact it did the opposite.
Throughout the nineteenth century, trilobites were almost the only known forms of earlycomplex life, and for that reason were assiduously collected and studied. The big mysteryabout them was their sudden appearance. Even now, as Fortey says, it can be startling to go tothe right formation of rocks and to work your way upward through the eons finding no visiblelife at all, and then suddenly “a whole Profallotaspis or Elenellus as big as a crab will popinto your waiting hands.” These were creatures with limbs, gills, nervous systems, probingantennae, “a brain of sorts,” in Fortey’s words, and the strangest eyes ever seen. Made ofcalcite rods, the same stuff that forms limestone, they constituted the earliest visual systemsknown. More than this, the earliest trilobites didn’t consist of just one venturesome speciesbut dozens, and didn’t appear in one or two locations but all over. Many thinking people inthe nineteenth century saw this as proof of God’s handiwork and refutation of Darwin’sevolutionary ideals. If evolution proceeded slowly, they asked, then how did he account forthis sudden appearance of complex, fully formed creatures? The fact is, he couldn’t.
Moreover, the record we do have is hopelessly skewed. Most land animals, of course, don’tdie in sediments. They drop in the open and are eaten or left to rot or weather down tonothing. The fossil record consequently is almost absurdly biased in favor of marine creatures.
Evolutionary success, it appeared, was a lottery.
One, writing in the New York Times Book Review, cheerfully suggested that as a result ofGould’s book scientists “have been throwing out some preconceptions that they had notexamined for generations. They are, reluctantly or enthusiastically, accepting the idea thathumans are as much an accident of nature as a product of orderly development.”
. . It was the fertile time when all the great ‘fundamental body plans’ were invented.
The feeling was that ultimately they weren’t terribly important to the development of lifeon 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) failedto move on to the next phase. The real business of complex life, in other words, started withthe Cambrian explosion. That’s how Gould saw it in any case.
And the reason we haven’t found these earlier species, it is now thought, is that they weretoo tiny to be preserved. Says Fortey: “It isn’t necessary to be big to be a perfectlyfunctioning, complex organism. The sea swarms with tiny arthropods today that have left nofossil record.” He cites the little copepod, which numbers in the trillions in modern seas andclusters in shoals large enough to turn vast areas of the ocean black, and yet our totalknowledge of its ancestry is a single specimen found in the body of an ancient fossilized fish.
But what he is remembered for now is an astute but lucky find in British Columbia, highabove the little town of Field, in the late summer of 1909. The customary version of the storyis that Walcott, accompanied by his wife, was riding on horseback on a mountain trail beneaththe spot called the Burgess Ridge when his wife’s horse slipped on loose stones. Dismountingto assist her, Walcott discovered that the horse had turned a slab of shale that contained fossilcrustaceans of an especially ancient and unusual type. Snow was falling—winter comes earlyto the Canadian Rockies—so they didn’t linger, but the next year at the first opportunityWalcott returned to the spot. Tracing the presumed route of the rocks’ slide, he climbed 750feet to near the mountain’s summit. There, 8,000 feet above sea level, he found a shaleoutcrop, about the length of a city block, containing an unrivaled array of fossils from soonafter the moment when complex life burst forth in dazzling profusion—the famous Cambrianexplosion. Walcott had found, in effect, the holy grail of paleontology. The outcrop becameknown as the Burgess Shale, and for a long time it provided “our sole vista upon the inceptionof modern life in all its fullness,” as the late Stephen Jay Gould recorded in his popular bookWonderful Life .
IT ISN’T EASY to become a fossil. The fate of nearly all living organisms—over 99.9percent of them—is to compost down to nothingness. When your spark is gone, everymolecule you own will be nibbled off you or sluiced away to be put to use in some othersystem. That’s just the way it is. Even if you make it into the small pool of organisms, the lessthan 0.1 percent, that don’t get devoured, the chances of being fossilized are very small.
Hallucigenia, it turned out, had been reconstructed upside down. Its stilt-like legs wereactually 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.
“In terms of trilobites?”
He took me to a gallery of tall metal cupboards. Each cupboard was filled with shallowdrawers, and each drawer was filled with stony trilobites—twenty thousand specimens in all.
Trilobites first appeared—fully formed, seemingly from nowhere—about 540 million yearsago, near the start of the great outburst of complex life popularly known as the Cambrianexplosion, and then vanished, along with a great deal else, in the great and still mysteriousPermian extinction 300,000 or so centuries later. As with all extinct creatures, there is anatural temptation to regard them as failures, but in fact they were among the most successfulanimals ever to live. Their reign ran for 300 million years—twice the span of dinosaurs,which were themselves one of history’s great survivors. Humans, Fortey points out, havesurvived so far for one-half of 1 percent as long.
Gould, ever scrupulous, discovered from reading Walcott’s diaries that the story of theBurgess Shale’s discovery appears to have been somewhat embroidered—Walcott makes nomention of a slipping horse or falling snow—but there is no disputing that it was anextraordinary find.
And yet that was exactly the conclusion to which many general reviewers were drawn.
Only about one bone in a billion, it is thought, ever becomes fossilized. If that is so, itmeans that the complete fossil legacy of all the Americans alive today—that’s 270 millionpeople with 206 bones each—will only be about fifty bones, one quarter of a completeskeleton. That’s not to say of course that any of these bones will actually be found. Bearing inmind that they can be buried anywhere within an area of slightly over 3.6 million squaremiles, little of which will ever be turned over, much less examined, it would be something ofa miracle if they were. Fossils are in every sense vanishingly rare. Most of what has lived onEarth has left behind no record at all. It has been estimated that less than one species in tenthousand has made it into the fossil record. That in itself is a stunningly infinitesimalproportion. However, if you accept the common estimate that the Earth has produced 30billion species of creature in its time and Richard Leakey and Roger Lewin’s statement (inThe Sixth Extinction ) that there are 250,000 species of creature in the fossil record, thatreduces the proportion to just one in 120,000. Either way, what we possess is the merestsampling of all the life that Earth has spawned.
In order to become a fossil, several things must happen. First, you must die in the rightplace. Only about 15 percent of rocks can preserve fossils, so it’s no good keeling over on afuture site of granite. In practical terms the deceased must become buried in sediment, whereit 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 bereplaced by dissolved minerals, creating a petrified copy of the original. Then as thesediments in which the fossil lies are carelessly pressed and folded and pushed about byEarth’s processes, the fossil must somehow maintain an identifiable shape. Finally, but aboveall, after tens of millions or perhaps hundreds of millions of years hidden away, it must befound and recognized as something worth keeping.
Unfortunately, according to Gould, Walcott failed to discern the significance of what hehad found. “Snatching defeat from the jaws of victory,” Gould wrote in another work, EightLittle Piggies, “Walcott then proceeded to misinterpret these magnificent fossils in the deepestpossible 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 aninterpretation,” Gould sighed, “life began in primordial simplicity and moved inexorably,predictably onward to more and better.”
Incidentally, Reginald Sprigg did eventually get a measure of overdue credit. One of themain early genera, Spriggina, was named in his honor, as were several species, and the wholebecame known as the Ediacaran fauna after the hills through which he had searched. By thistime, however, Sprigg’s fossil-hunting days were long over. After leaving geology he foundeda 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.
As for the revisions of the Burgess Shale fossils, almost at once people began to questionthe interpretations and, in particular, Gould’s interpretation of the interpretations. “From thefirst there were a number of scientists who doubted the account that Steve Gould hadpresented, however much they admired the manner of its delivery,” Fortey wrote in Life. Thatis putting it mildly.
Walcott died in 1927 and the Burgess fossils were largely forgotten. For nearly half acentury they stayed shut away in drawers in the American Museum of Natural History inWashington, seldom consulted and never questioned. Then in 1973 a graduate student fromCambridge University named Simon Conway Morris paid a visit to the collection. He wasastonished by what he found. The fossils were far more varied and magnificent than Walcotthad indicated in his writings. In taxonomy the category that describes the basic body plans ofall organisms is the phylum, and here, Conway Morris concluded, were drawer after drawer ofsuch anatomical singularities—all amazingly and unaccountably unrecognized by the manwho had found them.
But the real heat directed at Gould arose from the belief that many of his conclusions weresimply mistaken or carelessly inflated. Writing in the journal Evolution, Dawkins attackedGould’s assertions that “evolution in the Cambrian was a different kind of process fromtoday” and expressed exasperation at Gould’s repeated suggestions that “the Cambrian was aperiod of evolutionary ‘experiment,’ evolutionary ‘trial and error,’ evolutionary ‘false starts.’ .
Nine years later, in 1957, a schoolboy named John Mason, while walking throughCharnwood Forest in the English Midlands, found a rock with a strange fossil in it, similar toa modern sea pen and exactly like some of the specimens Sprigg had found and been trying totell everyone about ever since. The schoolboy turned it in to a paleontologist at the Universityof Leicester, who identified it at once as Precambrian. Young Mason got his picture in thepapers and was treated as a precocious hero; he still is in many books. The specimen wasnamed in his honor Chamia masoni.
And so matters seemed destined to remain forever until one day in 1909, three months shyof the fiftieth anniversary of the publication of Darwin’s On the Origin of Species , when apaleontologist named Charles Doolittle Walcott made an extraordinary find in the CanadianRockies.
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 Walcott was aninfant. As a boy Walcott discovered that he had a knack for finding fossils, particularlytrilobites, and built up a collection of sufficient distinction that it was bought by LouisAgassiz for his museum at Harvard for a small fortune—about $70,000 in today’s money.
What was most surprising, however, was that there were so many body designs that hadfailed to make the cut, so to speak, and left no descendants. Altogether, according to Gould, atleast fifteen and perhaps as many as twenty of the Burgess animals belonged to no recognizedphylum. (The number soon grew in some popular accounts to as many as one hundred—farmore 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, notthe conventional tale of steadily increasing excellence, complexity, and diversity.”
But that still left the enduring question of where all these animals had come from—howthey had suddenly appeared from out of nowhere.
“No, in terms of everything.”
In 1946 Sprigg was a young assistant government geologist for the state of South Australiawhen he was sent to make a survey of abandoned mines in the Ediacaran Hills of the FlindersRange, an expanse of baking outback some three hundred miles north of Adelaide. The ideawas to see if there were any old mines that might be profitably reworked using newertechnologies, so he wasn’t studying surface rocks at all, still less fossils. But one day whileeating his lunch, Sprigg idly overturned a hunk of sandstone and was surprised—to put itmildly—to see that the rock’s surface was covered in delicate fossils, rather like theimpressions leaves make in mud. These rocks predated the Cambrian explosion. He waslooking at the dawn of visible life.
Gould’s book was published in 1989 to general critical acclaim and was a great commercialsuccess. What wasn’t generally known was that many scientists didn’t agree with Gould’sconclusions 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 physiologicalfacts.
Strangest of all was the response of one of the heroes of Wonderful Life, Simon ConwayMorris, who startled many in the paleontological community by rounding abruptly on Gouldin a book of his own, The Crucible of Creation. The book treated Gould “with contempt, evenloathing,” in Fortey’s words. “I have never encountered such spleen in a book by aprofessional,” Fortey wrote later. “The casual reader of The Crucible of Creation, unaware ofthe history, would never gather that the author’s views had once been close to (if not actuallyshared with) Gould’s.”
This wasn’t, I should note, because of sloppiness or inattention. Interpreting the forms andrelationships of ancient animals on the basis of often distorted and fragmentary evidence isclearly a tricky business. Edward O. Wilson has noted that if you took selected species ofmodern insects and presented them as Burgess-style fossils nobody would ever guess that theywere all from the same phylum, so different are their body plans. Also instrumental in helpingrevisions were the discoveries of two further early Cambrian sites, one in Greenland and onein China, plus more scattered finds, which between them yielded many additional and oftenbetter specimens.
The Cambrian animals, it is now thought, were probably there all along, but were just toosmall to see. Once again it was trilobites that provided the clue—in particular that seeminglymystifying appearance of different types of trilobite in widely scattered locations around theglobe, all at more or less the same time.
I mention all this to explain why on a gray day in February I went to the Natural HistoryMuseum in London to meet a cheerful, vaguely rumpled, very likeable paleontologist namedRichard Fortey.
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 80,000; the normallyunimpeachable fact checkers of National Georgraphic say 60,000), which he brought back toWashington for further study. In both sheer numbers and diversity the collection wasunparalleled. Some of the Burgess fossils had shells; many others did not. Some were sighted,others blind. The variety was enormous, consisting of 140 species by one count. “The BurgessShale included a range of disparity in anatomical designs never again equaled, and notmatched today by all the creatures in the world’s oceans,” Gould wrote.
Nowadays, evolution just tinkers with old body plans. Back in the Cambrian, new phyla andnew classes arose. Nowadays we only get new species!”
Noting how often this idea—that there are no new body plans—is picked up, Dawkins says:
“The Cambrian explosion, if that’s the word for it, probably was more an increase in sizethan a sudden appearance of new body types,” Fortey says. “And it could have happened quiteswiftly, so in that sense I suppose it was an explosion.” The idea is that just as mammalsbided their time for a hundred million years until the dinosaurs cleared off and then seeminglyburst forth in profusion all over the planet, so too perhaps the arthropods and other triploblastswaited in semimicroscopic anonymity for the dominant Ediacaran organisms to have theirday. Says Fortey: “We know that mammals increased in size quite dramatically after thedinosaurs went—though when I say quite abruptly I of course mean it in a geological sense.
Many of the Burgess specimens have now been assigned to living phyla—just where Walcottput them in the first place. Hallucigenia and some others are thought to be related toOnychophora, a group of caterpillar-like animals. Others have been reclassified as precursorsof the modern annelids. In fact, says Fortey, “there are relatively few Cambrian designs thatare wholly novel. More often they turn out to be just interesting elaborations of well-established designs.” As he wrote in his book Life: “None was as strange as a present daybarnacle, nor as grotesque as a queen termite.”
Nor is it agreed that the Ediacaran organisms are in any way ancestral to anything alivetoday (except possibly some jellyfish). Many authorities see them as a kind of failedexperiment, a stab at complexity that didn’t take, possibly because the sluggish Ediacaranorganisms were devoured or outcompeted by the lither and more sophisticated animals of theCambrian period.
Today some of Sprigg’s original Ediacaran specimens, along with many of the other fifteenhundred specimens that have been found throughout theFlinders Range since that time, canbe seen in a glass case in an upstairs room of the stout and lovely South Australian Museumin Adelaide, but they don’t attract a great deal of attention. The delicately etched patterns arerather 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-bodiedoddities.”
The English team’s revisions showed that the Cambrian had been a time of unparalleledinnovation and experimentation in body designs. For almost four billion years life haddawdled along without any detectable ambitions in the direction of complexity, and thensuddenly, in the space of just five or ten million years, it had created all the basic bodydesigns still in use today. Name a creature, from a nematode worm to Cameron Diaz, and theyall use architecture first created in the Cambrian party.
With his supervisor, Harry Whittington, and fellow graduate student Derek Briggs, ConwayMorris spent the next several years making a systematic revision of the entire collection, andcranking out one exciting monograph after another as discovery piled upon discovery. Manyof the creatures employed body plans that were not simply unlike anything seen before orsince, but were bizarrely different. One, Opabinia, had five eyes and a nozzle-like snout withclaws on the end. Another, a disc-shaped being called Peytoia, looked almost comically like apineapple slice. A third had evidently tottered about on rows of stilt-like legs, and was so oddthat they named it Hallucigenia. There was so much unrecognized novelty in the collectionthat at one point upon opening a new drawer Conway Morris famously was heard to mutter,“Oh fuck, not another phylum.”
What happened was that the early Cambrian fossils began to undergo a period of criticalreappraisal. Fortey and Derek Briggs—one of the other principals in Gould’s book—used amethod known as cladistics to compare the various Burgess fossils. In simple terms, cladisticsconsists of organizing organisms on the basis of shared features. Fortey gives as an examplethe idea of comparing a shrew and an elephant. If you considered the elephant’s large size andstriking trunk you might conclude that it could have little in common with a tiny, sniffingshrew. But if you compared both of them with a lizard, you would see that the elephant andshrew were in fact built to much the same plan. In essence, what Fortey is saying is thatGould saw elephants and shrews where they saw mammals. The Burgess creatures, theybelieved, weren’t as strange and various as they appeared at first sight. “They were often nostranger than trilobites,” Fortey says now. “It is just that we have had a century or so to getused to trilobites. Familiarity, you know, breeds familiarity.”
In 1879 he took a job as a field researcher with the newly formed United States GeologicalSurvey and served with such distinction that within fifteen years he had risen to be its head. In1907 he was appointed secretary of the Smithsonian Institution, where he remained until hisdeath in 1927. Despite his administrative obligations, he continued to do fieldwork and towrite prolifically. “His books fill a library shelf,” according to Fortey. Not incidentally, hewas also a founding director of the National Advisory Committee for Aeronautics, whicheventually became the National Aeronautics and Space Agency, or NASA, and thus canrightly be considered the grandfather of the space age.
There is still very little agreement about what these things were or how they lived. Theyhad, as far as can be told, no mouth or anus with which to take in and discharge digestivematerials, and no internal organs with which to process them along the way. “In life,” Forteysays, “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 thanjellyfish. All the Ediacaran creatures were diploblastic, meaning they were built from twolayers of tissue. With the exception of jellyfish, all animals today are triploblastic.
“It was a strange time,” Fortey says now, “especially when you reflected that this was allabout something that happened five hundred million years ago, but feelings really did runquite high. I joked in one of my books that I felt as if I ought to put a safety helmet on beforewriting about the Cambrian period, but it did actually feel a bit like that.”
The upshot is that the Burgess fossils were found to be not so different after all.
