Abstract
The study of basicranial and endocranial characters in vertebrate paleontology has recently known a regain of interest. Indeed, these characters are renowed for their phylogenetic stability and are usually easily preserved in the fossil record. Here, the auditory region (Part I) and endocranium (Part II) of some fossil representatives of the mammalian order Afrotheria have been scanned using X-ray (micro)tomography, described and compared to their modern day's counterparts. These fossil afrotheres are the Bibymalagasia (Chapter 1), the stem sengi Chambius (Chapter 2), numerous Hyracoidea (Chapter 3) and stem Tethytheria such as the proboscideans Numidotherium, the embrithopod Arsinoitherium and the sirenian Prorastomus (Chapter 4). This study highlights the strong phylogenetic signal carried by the characters of the auditory region and endocast, which could even support some molecular clades (e.g. Afroinsectivora, ‘Panelephantulus'). It also shows that convergences can occur under certain selective pressure (e.g. in Tethytheria). Finally this study brings new clues that support the hypothesis of an African origin of Afrotheria as well as that of an ‘ungulate-like' instead of ‘insectivore-like' ancestor. These inferences based on the observation of the oldest and basal-most fossil representatives of this group are crucial to understand the origin, evolution and diversification of afrotherian and placental mammals across the Cenozoic.