A small catarrhine talus from the middle Miocene Nachola, northern Kenya

Abstract

We describe a small catarrhine talus discovered in Nachola, northern Kenya. Although Nacholapithecus, Nyanzapithecus, and Victoriapithecus are known from Nachola, this talus is too tiny to be assigned to a female Nacholapithecus. It is also different in shape from both Nacholapithecus and Victoriapithecus. Hence, it is best to assign it to Nyanzapithecus, whose tarsal features were not known before. We compared this talus to tali of other small Miocene catarrhines from Kenya and several extant catarrhines. The estimated body mass of this specimen is 5.2–5.5 kg, depending on the regression formula. It is distinguished from comparative taxa by the feeble development of the malleolar cup, which is a stabilizing mechanism of the talocrural joint at the full dorsiflexion, and a low trochlea, suggesting that the talocrural joint was not specialized for rapid extension-flexion. These features suggest that Nyanzapithecus walked and ran in the trees with less agility and did not frequently engage in leaping. Additionally, it has a wide posteroinferior surface of the trochlea with a straight lateral border, probably enhancing the talocrural joint’s full plantarflexion. This might be suggestive of hindlimb suspension.