of toad；newt； salamander； or other amphibian went extinct in north america。 “why should thesedelicate creatures have emerged unscathed from such an unparalleled disaster？” asks timflannery in his fascinating prehistory of america； eternal frontier。
in the seas it was much the same story。 all the ammonites vanished； but their cousins thenautiloids； who lived similar lifestyles； swam on。 among plankton； some species werepractically wiped out—92 percent of foraminiferans； for instance—while other organisms likediatoms； designed to a similar plan and living alongside； were paratively unscathed。
these are difficult inconsistencies。 as richard fortey observes： “somehow it does notseem satisfying just to call them ‘lucky ones’ and leave it at that。” if； as seems entirely likely；the event was followed by months of dark and choking smoke； then many of the insectsurvivors bee difficult to account for。 “some insects； like beetles；” fortey notes； “couldlive on wood or other things lying around。 but what about those like bees that navigate bysunlight and need pollen？ explaining their survival isn’t so easy。”
above all； there are the corals。 corals require algae to survive and algae require sunlight；and both together require steady minimum temperatures。 much publicity has been given in thelast few years to corals dying from changes in sea temperature of only a degree or so。 if theyare that vulnerable to small changes； how did they survive the long impact winter？
there are also many hard…to…explain regional variations。 extinctions seem to have been farless severe in the southern hemisphere than the northern。 new zealand in particular appears to have e through largely unscathed even though it had almost no burrowing creatures。 evenits vegetation was overwhelmingly spared； and yet the scale of conflagration elsewheresuggests that devastation was global。 in short； there is just a great deal we don’t know。
some animals absolutely prospered—including； a little surprisingly； the turtles once again。
as flannery notes； the period immediately after the dinosaur extinction could well be knownas the age of turtles。 sixteen species survived in north america and three more came intoexistence soon after。
clearly it helped to be at home in water。 the kt impact wiped out almost 90 percent ofland…based species but only 10 percent of those living in fresh water。 water obviously offeredprotection against heat and flame； but also presumably provided more sustenance in the leanperiod that followed。 all the land…based animals that survived had a habit of retreating to asafer environment during times of danger—into water or underground—either of whichwould have provided considerable shelter against the ravages without。 animals thatscavenged for a living would also have enjoyed an advantage。 lizards were； and are； largelyimpervious to the bacteria in rotting carcasses。 indeed； often they are positively drawn to it；and for a long while there were clearly a lot of putrid carcasses about。
it is often wrongly stated that only small animals survived the kt event。 in fact； among thesurvivors were crocodiles； which were not just large but three times larger than they are today。
but on the whole； it is true； most of the survivors were small and furtive。 indeed； with theworld dark and hostile； it was a perfect time to be small； warm…blooded； nocturnal； flexible indiet； and cautious by nature—the very qualities that distinguished our mammalian forebears。
had our evolution been more advanced； we would probably have been wiped out。 instead；mammals found themselves in a world to which they were as well suited as anything alive。
however； it wasn’t as if mammals swarmed forward to fill every niche。 “evolution mayabhor a vacuum；” wrote the paleobiologist steven m。 stanley； “but it often takes a long timeto fill it。” for perhaps as many as ten million years mammals remained cautiously small。 inthe early tertiary； if you were the size of a bobcat you could be king。
but once they got going； mammals expanded prodigiously—sometimes to an almostpreposterous degree。 for a time； there were guinea pigs the size of rhinos and rhinos the sizeof a two…story house。 wherever there was a vacancy in the predatory chain； mammals rose（often literally） to fill it。 early members of the raccoon family migrated to south america；discovered a vacancy； and evolved into creatures the size and ferocity of bears。 birds； too；prospered disproportionately。 for millions of years； a gigantic； flightless； carnivorous birdcalled titanis was possibly the most ferocious creature in north america。 certainly it was themost daunting bird that ever lived。 it stood ten feet high； weighed over eight hundred pounds；and had a beak that could tear the head off pretty much anything that irked it。 its familysurvived in formidable fashion for fifty million years； yet until a skeleton was discovered inflorida in 1963； we had no idea that it had ever existed。
which brings us to another reason for our uncertainty about extinctions： the paltriness ofthe fossil record。 we have touched already on the unlikelihood of any set of bones beingfossilized； but the record is actually worse than you might think。 consider dinosaurs。
museums give the impression that we have a global abundance of dinosaur fossils。 in fact；overwhelmingly museum displays are artificial。 the giant diplodocus that dominates theentrance hall of the natural history museum in london and has delighted and informedgenerations of visitors is made of plaster—built in 1903 in pittsburgh and presented to the museum by andrew carnegie。 the entrance hall of the american museum of natural historyin new york is dominated by an even grander tableau： a skeleton of a large barosaurusdefending her baby from attack by a darting and toothy allosaurus。 it is a wonderfullyimpressive display—the barosaurus rises perhaps thirty feet toward the high ceiling—but alsoentirely fake。 every one of the several hundred bones in the display is a cast。 visit almost anylarge natural history museum in the world—in paris； vienna； frankfurt； buenos aires；mexico city—and what will greet you are antique models； not ancient bones。
the fact is； we don’t really know a great deal about the dinosaurs。 for the whole of the ageof dinosaurs； fewer than a thousand species have been identified （almost half of them knownfrom a single specimen）； which is about a quarter of the number of mammal species alivenow。 dinosaurs； bear in mind； ruled the earth for roughly three times as long as mammalshave； so either dinosaurs were remarkably unproductive of species or we have barelyscratched the surface （to use an irresistibly apt cliché）。
for millions of years through the age of dinosaurs not a single fossil has yet been found。
even for the period of the late cretaceous—the most studied prehistoric period there is；thanks to our long interest in dinosaurs and their extinction—some three quarters of allspecies that lived may yet be undiscovered。 animals bulkier than the diplodocus or moreforbidding than tyrannosaurus may have roamed the earth in the thousands； and we maynever know it。 until very recently everything known about the dinosaurs of this period camefrom only about three hundred specimens representing just sixteen species。 the scantiness ofthe record led to the widespread belief that dinosaurs were on their way out already when thekt impact occurred。
in the late 1980s a paleontologist from the milwaukee public museum； peter sheehan；decided to conduct an experiment。 using two hundred volunteers； he made a painstakingcensus of a well…defined； but also well…picked…over； area of the famous hell creek formationin montana。 sifting meticulously； the volunteers collected every last tooth and vertebra andchip of bone—everything that had been overlooked by previous diggers。 the work took threeyears。 when finished they found that they had more than tripled the global total of dinosaurfossils from the late cretaceous。 the survey established that dinosaurs remained numerousright up to the time of the kt impact。 “there is no reason to believe that the dinosaurs weredying out gradually during the last three million years of the cretaceous；” sheehan reported。
we are so used to the notion of our own inevitability as life’s dominant species that it ishard to grasp that we are here only because of timely extraterrestrial bangs and other randomflukes。 the one thing we have in mon with all other living things is that for nearly fourbillion years our ancestors have managed to slip through a series of closing doors every timewe needed them to。 stephen jay gould expressed it succinctly in a well…known line： “humansare here today because our particular line never fractured—never once at any of the billionpoints that could have erased us from history。”
we started this chapter with three points： life wants to be； life doesn’t always want to bemuch； life from time to time goes extinct。 to this we may add a fourth： life goes on。 andoften； as we shall see； it goes on in ways that are decidedly amazing。
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23THE RICHNESS OF BEING
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here and there in the natural history museum in london； built into recesses along theunderlit corridors or sta