Cuvier's work is considered the foundation of vertebrate paleontology, and he expanded Linnaean taxonomy by grouping classes into phyla and incorporating both fossils and living species into the classification. Cuvier is also known for establishing extinction as a fact—at the time, extinction was considered by many of Cuvier's contemporaries to be merely controversial speculation. In his Essay on the Theory of the Earth (1813) Cuvier proposed that now-extinct species had been wiped out by periodic catastrophic flooding events. In this way, Cuvier became the most influential proponent of catastrophism in geology in the early 19th century. His study of the strata of the Paris basin with Alexandre Brongniart established the basic principles of biostratigraphy.
Among his other accomplishments, Cuvier established that elephant-like bones found in the USA belonged to an extinct animal he later would name as a mastodon, and that a large skeleton dug up in Paraguay was of Megatherium, a giant, prehistoric ground sloth. He named the pterosaur Pterodactylus, described (but did not discover or name) the aquatic reptile Mosasaurus, and was one of the first people to suggest the earth had been dominated by reptiles, rather than mammals, in prehistoric times.
Cuvier is also remembered for strongly opposing theories of evolution, which at the time (before Darwin's theory) were mainly proposed by Jean-Baptiste de Lamarck and Geoffroy Saint-Hilaire. Cuvier believed there was no evidence for evolution, but rather evidence for cyclical creations and destructions of life forms by global extinction events such as deluges. In 1830, Cuvier and Geoffroy engaged in a famous debate, which is said to exemplify the two major deviations in biological thinking at the time – whether animal structure was due to function or (evolutionary) morphology. Cuvier supported function and rejected Lamarck's thinking.
His most famous work is Le Règne Animal (1817; English: The Animal Kingdom). In 1819, he was created a peer for life in honor of his scientific contributions. Thereafter, he was known as Baron Cuvier. He died in Paris during an epidemic of cholera. Some of Cuvier's most influential followers were Louis Agassiz on the continent and in the United States, and Richard Owen in Britain. His name is one of the 72 names inscribed on the Eiffel Tower.
Cuvier was born in Montbéliard, France (in department of Doubs), where his Protestant ancestors had lived since the time of the Reformation. His father, Jean George Cuvier, was a lieutenant in the Swiss Guards and a bourgeois of the town of Montbéliard; his mother was Anne Clémence Chatel. At the time, the town, which was annexed to France on 10 October 1793, belonged to the Duchy of Württemberg. His mother, who was much younger than his father, tutored him diligently throughout his early years, so he easily surpassed the other children at school. During his gymnasium years, he had little trouble acquiring Latin and Greek, and was always at the head of his class in mathematics, history, and geography. According to Lee, "The history of mankind was, from the earliest period of his life, a subject of the most indefatigable application; and long lists of sovereigns, princes, and the driest chronological facts, once arranged in his memory, were never forgotten."