in the Italian mountains. He interpreted them as the remains of ancient shells, and he argued that the sea had once covered these areas.
Later, Nicolaus Steno (or Niels Stensen) (1638-1686) demonstrated the true nature of glossopetrae simply by dissecting the head of a huge modern shark, and showing that its teeth were identical to the fossils (Fig. 1.7). Robert Hooke (1625-1703), a contemporary of Steno's, also gave detailed descriptions of fossils, using a crude microscope to compare the cellular structure of modern and fossil wood, and the crystalline layers in the shell of a modern and a fossil mollusk. This simple descriptive work showed that magical explanations of fossils were without foundation.
The idea of extinction_
Robert Hooke was one of the first to hint at the idea of extinction, a subject that was hotly debated during the 18 th century. The debate fizzed quietly until the 1750s and 1760s when accounts of fossil mastodon remains from North America began to appear. Explorers sent large teeth and bones back to Paris and London for study by the anatomic experts of the day (normal practice at the time, because the serious pursuit of science as a profession had not yet begun in North America). William Hunter noted in 1768 that the "American incognitum" was quite different from modern elephants and from mammoths, and was clearly an extinct animal, and a meat-eating one at that. "And if this animal was indeed carnivorous, which I believe cannot be doubted, though we may as philosophers regret it," he wrote, "as men we cannot but thank Heaven that its whole generation is probably extinct."
The reality of extinction was demonstrated by the great French natural scientist Georges Cuvier (1769-1832). He showed that the mammoth from Siberia and the mastodon from North America were unique species, and different from the modern African and Indian elephants (Fig. 1.8). Cuvier extended his studies to the rich Eocene mammal deposits of the Paris Basin, describing skeletons of horse-like animals (see Fig. 1.4), an opossum, carnivores, birds and reptiles, all of which differed markedly from living forms. He also wrote accounts of Mesozoic crocodilians, pterosaurs and the giant mosasaur of Maastricht.
Cuvier is sometimes called the father of comparative anatomy; he realized that all organisms share common structures. For example, he showed that elephants, whether living or fossil, all share certain anatomic features. His public demonstrations became famous: he claimed to be able to identify and reconstruct an animal from just one tooth or bone, and he was usually successful. After 1800, Cuvier had established the reality of extinction.
The vastness of geological time_
Many paleontologists realized that the sedimentary rocks and their contained fossils
Figure 1.8 Proof of extinction: Cuvier's comparison of (a) the lower jaw of a mammoth and (b) a modern Indian elephant. (Courtesy of Eric Buffetaut.)
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