First African record of the Miocene Asian mouse-deer Siamotragulus (Mammalia, Ruminantia, Tragulidae): implications for the phylogeny and evolutionary history of the advanced selenodont tragulids
New remains of the small tragulid Dorcatherium songhorensis Whitworth, 1958 from the Early Miocene fossil site of Napak XXI (Uganda) include the first significant sample of postcranial bones from this species ever described. The limb bones of this tragulid are very similar to that described in the Miocene Asian long-legged tragulids of the genus Siamotragulus Thomas et al., 1990, a type previously unknown in the African Miocene. A cladistic analysis links D. songhorensis to a Siamotragulus clade as its basal offshoot, so we propose the name Siamotragulus songhorensis (Whitworth, 1958) for this species. Also, the Siamotragulus clade belongs to a monophyletic group that includes Afrotragulus Sánchez et al., 2010 and the extant Asian genera Moschiola and Tragulus. This inclusive clade is characterized by both a derived selenodont dentition and an advanced postcranial skeleton. Additionally Siamotragulus shows some cursorial refinements reflected in its postcranial skeleton including the pecoran-like metatarsals III–IV. Siamotragulus songhorensis shows that the genus Siamotragulus was not endemic to Asia as previously thought, and that a highly diverse guild of tragulids, including different members of the advanced selenodont clade, inhabited Africa as early as the Early Miocene (19–20 Ma).