Hyracoidea from the Oligocene of Topernawi, Turkana Basin, Kenya

The Topernawi area of west Turkana, northern Kenya, preserves a number of recently discovered vertebrate fossil localities of mid-Oligocene age. The Topernawi fauna provides important new data on mammalian evolution in equatorial eastern Africa during the mid-Cenozoic. Here, we describe five new species of hyracoids from Topernawi: Nengohyrax josephi, Abdahyrax philipi, Geniohyus ewoii, Thyrohyrax lokutani, and Thyrohyrax ekaii. These species range in reconstructed body mass from ∼8 to ∼150 kg, comparable to the body size range that has been observed at other hyracoid-rich Paleogene sites. We use Bayesian tip-dating phylogenetic analyses to estimate hyracoid relationships. We find that non-Thyrohyrax species from Topernawi are members of Geniohyidae, a clade of bunodont, Paleogene hyracoids. Despite being approximately the same age as some of the youngest and best-sampled horizons in the Jebel Qatrani Formation (Fayum, northern Egypt), the Topernawi hyracoid fauna is distinct, and shows no overlap at the species level; it also shows no species overlap with the ∼1.5–2.5 Ma younger Chilga localities in northern Ethiopia. The hyracoid assemblage from Topernawi adds to a growing body of evidence which suggests that certain distinctive clades known from earlier Oligocene horizons in northern Africa (Saghatherium, Selenohyrax, Titanohyrax) did not persist into the late Oligocene.