Proximal femoral anatomy of omomyiform primates

Compared to the adapid primates, the limb skeleton of omomyiforms is only poorly represented. With the discovery of some new material, the proximal femur is now known in several taxa, including representatives from both of the recognized families. We describe the femur of a very small North American omomyid from the Bridger formation (middle Eocene) and compare its anatomy with the omomyine Hemiacodon and the European microchoerids Nannopithex, Necrolemur and Microchoerus. Tarsius and omomyiforms share several features of the proximal femur which are correlated with frequent leaping in small primates, and which may be morphotypic for Tarsiiformes. Hemiacodon and the new small omomyid are quite similar to each other in that they both have a semicylindrical femoral head which, although more advanced than most primates, is not as derived as the fully cylindrical form exhibited by galagos and tarsiers. As with other areas of the postcranium, microchoerids are very distinct from North American omomyiforms. Microchoerus and Necrolemur exhibit features which are otherwise seen primarily in anthropoid primates such as a marked posterior projection of the lesser trochanter. In addition, Necrolemur shares a unique construction of the intertrochanteric crest with parapithecids. Despite these and other intriguing similarities of the postcranial skeleton, any relationship between microchoerids and early anthropoids is difficult to establish because of other marked differences between them.