The Earliest Fossil of the African Clawed Frog (Genus Xenopus) from Sub-Saharan Africa

Although the fossil record of pipoid frogs is more extensive than for other anuran clades, crown-group genera are poorly documented throughout the Cenozoic. We report an isolated neurocranium from the Nsungwe Formation (∼25 million years ago; Oligocene) in southwestern Tanzania, providing the earliest evidence for the genus Xenopus in sub-Saharan Africa. The specimen is well preserved, allowing us to use three-dimensional geometric morphometrics to compare the shape of this neurocranium to those of all extant species of Xenopus based on microcomputed tomography scans. Analyses revealed that this small fossil resembles diminutive extant species of Xenopus such as X. longipes. The fossil neurocranium preserves well-ossified tectum nasi and septum nasi, the latter separating large ovoid olfactory foramina, contributing to a more-ossified region surrounding the prootic foramen than observed in extant species of similar size. The Nsungwe Formation pipoid fossil contributes new information to the early biogeography and body-size diversification within the genus Xenopus.