Museum of Natural History, Jean-Baptiste Lamarck. According to Lamarck, there was a force-the “power of life” -that pushed organisms to become increasingly complex. At the same time, animals and also plants often had to cope with changes in their environment. They did so by adjusting their habits; these new habits, in turn, produced physical modifications that were then passed down to their offspring.
Like his view of transformisme, Cuvier’s belief in cataclysm fit with-indeed, could be said to follow from his convictions about anatomy. Since animals were functional units, ideally suited to their circumstances, there was no reason why, in the ordinary course of events, they should die out. Not even the most devastating events known to occur in the contemporary world -volcanic eruptions, say, or forest fires–were sufficient to explain extinction; confronted with such changes, organisms simply moved on and sur-vived. The changes that had caused extinctions must therefore have been of a much greater magnitude so great that animals had been unable to cope with them. That such extreme events had never been observed by him or any other naturalist was another indication of nature’s mutability: in the past, it had operated differently more intensely and more savagely than it did at present.
At the same time, some of Cuvier’s most wild-sounding claims have turned out to be surprisingly accurate. Life on earth has been disturbed by “terrible events,” and “organisms without number” have been their victims. Such events cannot be explained by the forces, or “agents,” at work in the present. Nature does, on occasion, “change course,” and at such moments, it is as if the “thread of operations” has been broken.
Toward the end of the Beagle’s voyage, Darwin encountered coral reefs. These provided him with his first major breakthrough a startling idea that would ease his entrée into London’s scientific circles. Darwin saw that the key to understanding coral reefs was the interplay between biology and geology. If a reef formed around an island or along a continental margin that was slowly sinking the corals, by growing slowly upward, could maintain their position relative to the water. Gradually, as the land subsided, be corals would form a barrier reef. If, eventually, the land sank away entirely, the reef would form an atoll.
Darwin’s account went beyond and to a certain extent contradicted Lyell’s; the older man had hypothesized that reefs grew from the rims of submerged volcanoes. But Darwin’s ideas were so fundamentally Lyellian in nature that when, upon his return to England, Darwin presented them to Lyell, the latter was delighted.
No one had ever seen a new species produced, nor, according to Darwin, should they expect to. Speciation was so drawn out as to be, for all intents and purposes, unobservable. “We see nothing of these slow changes in progress,” he wrote. It stood to reason that extinction should have been that much more difficult to wit-ness. And yet it wasn’t. In fact, during the years Darwin spent holed up at Down House, developing his ideas about evolution, the very last individuals of one of Europe’s most celebrated species, the great auk, disappeared.
Among the facts he related to Darwin was that on each of the islands in the Galápagos the tortoises had different-shaped shells. On this basis, Lawson claimed that he could “pronounce from which island any tortoise may have been brought.” Lawson also told Darwin that the tortoises’ days were numbered. The islands were frequently visited by whaling ships, which carried the huge beasts off as portable provisions. Just a few years earlier, a frigate visiting Charles Island had left with two hundred tortoises stowed in its hold. As a result, Darwin noted in his diary, “the numbers have been much reduced.” By the time of the Beagle’s visit, tortoises had become so scarce on Charles Island that Darwin, it seems, did not see a single one. Lawson predicted that Charles’s tortoise, known today by the scientific name Chelonoidis elephant-pus, would be entirely gone within twenty years. In fact, it probably disappeared in fewer than ten. (Whether Chelonoidis elephantopus was a distinct species or a subspecies is still a matter of debate.)
During the late Cretaceous, the park, the creek bed, and everything around us for many kilometers would have been under water. At that point, the world was very warm-lush forests grew in the Arctic- -and sea levels were high. Most of New Jersey formed part of the continental shelf of what’s now eastern North America, which, as the Atlantic was then much narrower, was considerably closer to what’s now Europe.
AmMOnITeS floated through the world’s shallow oceans for more than three hundred million years, and their fossilized shells turn up all around the world. Pliny the Elder, who died in the eruption that buried Pompeii, was already familiar with them, although he considered them to be precious stones. (The stones, he related in his Natural History, were said to bring prophetic dreams.) In medieval England, ammonites were known as “serpent stones,” and in Germany they were used to treat sick cows. In India, they were and to a certain extent still are revered as manifestations of Vishnu.
It’s impossible to give anything close to a full account of the various species, genera, families, and even whole orders that went extinct at the K-I boundary. On land, every animal larger than a cat seems to have died out. The event’s most famous victims, the dinosaurs–or, to be more precise, the non-avian dinosaurs-suffered a hundred percent losses. Among the groups that were probably alive right up to the end of the Cretaceous were such familiar museum shop fixtures as hadrosaurs, ankylosaurs, tyrannosauruses, and triceratops. Pterosaurs, too, disappeared. Birds were also hard-hit; perhaps three-quarters of all bird families, perhaps more, went extinct. Enantiornithine birds, which retained such archaic features as teeth, were wiped out, as were Hesperornithine birds, which were aquatic and for the most part flightless. The same goes for lizards and snakes; around four-fifths of all species vanished. Mammals ranks, too, were devastated; something like two-thirds of the mammalian families living at the end of the Cretaceous disappear at the boundary.
Source : The Sixth Extinction: An Unnatural History by Elizabeth Kolbert
Goodreads : https://www.goodreads.com/book/show/17910054-the-sixth-extinction
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