African wet habitats during the Neogene: contribution of the large semiaquatic and potamophilous mammals. This type of habitat played a central role in the ecological and biogeographical history of hominids. The selected environmental markers (hippopotamuses, pigs), in association with human fossils and behavioral evidence, will allow me to reconstruct the evolution of wet habitats and of hydrographical networks.
Hippopotamids are large mammals, with short, stumpy legs, and barrel-shaped bodies. They have large heads, with broad mouths, and nostrils placed at the top of the snout. Like pigs, they have four toes, but unlike pigs, all of the toes are used in walking. Hippopotamids are unguligrade, although, unlike most other such animals, they have no hooves, instead using a pad of tough connective tissue. Their stomach has three chambers, but they are not true ruminants. The living species are both smooth-skinned, and lack both sebaceous glands and sweat glands. The outer epidermis is relatively thin, so that hippos dehydrate rapidly in dry environments.
Hippos have rotund bodies and short legs. Unlike other artiodactyls, which have only two functional hooves, there are four toes on each foot with slight webbing between them. The thick skin appears hairless apart from a few bristles around the mouth and on the tail, but there is a covering of very fine hairs at low density over the whole of the body. There are no sweat glands as such, but there are large skin glands that secrete a viscous liquid that turns pink on exposure to air. The secretion probably acts as a sunscreen; it is also thought to have antiseptic properties. The skin needs to be kept wet, and cracks appear if the hippo is prevented from entering water.
