Dental and tarsal morphology of the European Paleocene/Eocene 'condylarth' mammal Microhyus

摘要

New dental and postcranial remains of the alleged louisinine hyopsodontid '' condylarth '' Microhytis from the European Paleocene/Eocene transition are described, and prompt a reevaluation of the genus. New specimens belonging to Microkyus musculus from Dormaal (MP7, Belgium) provide the first evidence of the lower dentition of the type species. We describe M. musculus? from Pourcy (MP7, France) and cf. Microhyus sp. from Berru (MP6a, France). A rich original assemblage of M. reisi from Silveirinha (MP7 Portugal) allows a detailed description of the morphological dental variation within that species. Well-preserved astragali and calcanei from Silveirinha can be confidently attributed to Microhytis reisi. Functional analysis of these elements suggests that Microhyus was a terrestrial mammal capable of rapid running or jumping. The pedal morphology of Microhyus is very similar to that of Paschatherium. These louisinines share some derived characters with the hyopsodontids Apheliscus and Haplomylus (e.g., the occurrence of a cotylar fossa on the astragalus) but they differ from Hyopsodus. Therefore, in view of the pedal morphology alone. the hyopsodontids may be polyphyletic. Given the dental similarities between Microhyus mid the early representatives of the order Macroscelidea, we compared the tarsal morphology of louisinines with that of modern macroscelidids (Paleogene tarsal remains are currently unknown for this group). Macroscelidids and louisinines present some similarities in their astragalar morphology; however, the microscelidid astragalus appears to be too specialized to be compared with that of Microhyus and Paschatherium.