Illustration of skeleton of a hippopotamus, (Hippopotamus amphibius) skelton, copperplate engraving from Cuvier's 'Ossamens Fossiles'. Cuvier saw that the key to understanding fossils was to relate their bones to animals currently known. In this he was the father of comparative anatomy - a field that was to be crucial to the founding of modern biology. Here a hippo provides reference for the even larger bones of the extinct megafauna that was lately being discovered in the environs of Paris and elsewhere. Cuvier actually mistook some of the first iguanodon bone material discovered by Gideon Mantell (and shown to him by Chrles Lyell) for that of a hippo, but he later changed his mind and gave Mantell credit for the discovery.