How did Mary Anning's cliff finds help prove that species can vanish?

Mary Anning helped prove it with bones that matched nothing alive. Georges Cuvier had argued for extinction in the late 1790s from fossils such as mammoths, but in the early 1820s many scientifically literate people still believed that existing species did not become extinct, just as new ones did not appear. Odd fossils were explained away as animals still living somewhere unexplored. Then Anning, from Lyme Regis, pulled out skeletons so unlike any known living creature that they struck a major blow against that idea.

Her father was a cabinetmaker who dug the nearby cliffs for fossils and sold them to tourists. In 1811 her brother Joseph dug up a 4-foot ichthyosaur skull, and in 1812, when Mary was 12, she found the rest of the skeleton, over 5 yards long. Later she found the first complete plesiosaur, in 1823, and the first British pterosaur, in 1828.

The cliffs are the Blue Lias, alternating limestone and shale laid down on a shallow seabed early in the Jurassic, about 210 to 195 million years ago. Collectors came in winter, because landslides then exposed new fossils. In October 1833 a landslide buried her terrier, Tray, her constant companion, and she barely avoided being killed herself.

She was also a careful scientist. She dissected fish and cuttlefish to understand her fossils, and she suggested that mysterious stones called bezoar stones were really fossilised faeces, which William Buckland named coprolites. Yet the Geological Society of London would not let her in, even as a guest, and the gentlemen who published descriptions of her finds often left out her name.