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Abstract
Macroscelidea (elephant-shrews or sengis) are small insectivorous mammals restricted to Africa; they belong to the super-cohort Afrotheria along with other insectivorans (aardvarks, tenrecs and golden moles) and ungulates (elephants, sea cows and hyraxes). Though their fossil record extends back to the Eocene, cranial remains of Palaeogene elephant-shrews, including the middle and inner ear structure, remain unknown. Two macroscelid isolated petrosal bones are described from the late Early–early Middle Eocene Djebel Chambi locality in Tunisia. Chambius kasserinensis is the only macroscelid represented in this locality. A cladistic analysis based on petrosal and inner ear characters highlights the crucial interest of the petrosal and inner ear morphology for understanding the evolution of Macroscelididae. It confirms the attribution of these isolated petrosals to C. kasserinensis. This hypothesis is supported by a common pattern of circulatory system, the morphology of the rostral and caudal tympanic processes, and the shape of the cochlea. In addition, Chambius appears to be the basal-most taxon among the macroscelid sample; this position is supported by the lack of some specializations of the middle ear such as inflated ossicular bones and pneumatized bulla. The presence of a secondary common crus in Chambius suggests a convergent loss of this structure, at least in Macroscelidea and Tenrecoidea. The petrosal and inner ear characters support the clade Afroinsectivora, which gathers macroscelids with other endemic African insectivorans (tenrecs and golden moles), reinforcing the hypothesis of an African origin of macroscelids. The petrosal bone and inner ear characters provide further morphological support for the debated clade (Petrodromus, Elephantulus rozeti, Macroscelides). New data underlines the fact that the cranial arterial pattern of the Eocene macroscelid Chambius was already similar to that of modern macroscelid species. It also suggests that early elephant-shrews were probably not as capable of hearing low frequencies as their extant representatives.