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leaf in wet mud； or depose 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。
only about one bone in a billion； it is thought； ever bees fossilized。 if that is so； itmeans that the plete 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 pleteskeleton。 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 mon 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。
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。
about 95 percent 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 gray day in february i went to the natural historymuseum in london to meet a cheerful； vaguely rumpled； very likeable paleontologist namedrichard fortey。
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。
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 es the name。 fortey found hisfirst when he was a boy clambering over rocks at st。 david’s bay in wales。 he was hookedfor life。
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。
“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 aplete trilobite fossil is still a big moment for a paleontologist。”
trilobites first appeared—fully formed； seemingly from nowhere—about 540 million yearsago； near the start of the great outburst of plex 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。
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。”
“in terms of trilobites？”
“no； in terms of everything。”
throughout the nineteenth century； trilobites were almost the only known forms of earlyplex 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 of calcite 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 plex； fully formed creatures？ the fact is； he couldn’t。
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 o