Ecomorphological diversity among Paleogene hyracoids (Mammalia): a new cursorial browser from the Fayum, Egypt

ABSTRACT

A new genus and species (Antilohyrax pectidens) of gazelle-sized hyracoid from the late Eocene, Jebel Qatrani Formation, Fayum Province, Egypt, exhibits dental, cranial and postcranial specializations unique among hyracoids. The lower incisors are broad, hyper-pectinate teeth similar to those of the extant dermopteran genus Cynocephalus. Upper incisors are apparently absent, and the shape of the premaxilla suggests that the lower incisors occluded against an upper fibrous pad, as in Cynocephalus and ruminants. The cheek teeth are dominated by sharp-edged, crescentic shearing blades, suggesting a folivorous diet. The articulation between the astragalus and navicular is furrowed and condylar in shape, allowing notable midtarsal flexion and extension but limited lateral movement. The tibia and fibula are fused together throughout most of their length. In size and proportions, limb elements resemble those of the extant springbok (Antidorcas marsupialis, Bovidae). Functional inferences derived from these features suggest a cursorial browser, a Paleogene analog to the bovids that do not appear in Africa until the Miocene. The new genus and species adds another adaptive dimension to what was already an extremely diverse record of Tertiary hyracoids, and further underscores that hyracoids were the dominant terrestrial ungulates of the African Paleogene.