The distal tibia of primates with special reference to the omomyidae

The morphology of the distal tibia and its joint surfaces is described in the late Eocene European Necrolemur, the middle Eocene North American Hemiacodon, and an omomyid species from the lower part of the Bridger Formation of North America. Necrolemur, like Tarsius, exhibits tibiofibular fusion, although to a less advanced degree. The Bridger omomyids, however, show no evidence of fusion but are similar to galagos in the conformation of this joint. The distal tibia of euprimates is distinguished by several derived features. These correlate with derived features of the astragalus and are functionally related to the abduction of the foot that accompanies dorsiflexion in primates. Tarsius, omomyids, and anthropoids share a suite of features which distinguish them from strepsirhines; these may be haplorhine synapomorphies, but the polarity of these features is difficult to determine. If they are synapomorphies, abduction accompanying dorsiflexion and movement at the inferior tibiofibular joint were restricted in ancestral haplorhines. In living primates such restriction is associated with small body size and saltatorial locomotion.