New skeletal remains of Omomys (Primates, Omomyidae): functional morphology of the hindlimb and locomotor behavior of a Middle Eocene primate.
New associated craniodental and postcranial remains of Omomys carteri from Bridger C beds in Uinta County, Wyoming represent the largest and most nearly complete single taxon sample of omomyid postcranial fossils presently known. They allow, for the first time, a description and detailed analysis of the functional morphology of the hindlimb of this middle Eocene omomyine primate. Comparisons of pelvic, femoral, tibial, and pedal morphology and metrics with a large sample of prosimian primates of known locomotor behavior suggest that Omomys possessed a highly distinctive mosaic of functional adaptations related to active quadrupedalism and leaping. Traits suggestive of quadrupedalism include the lengths of the ischium and ilium, position of the femoral trochanters, and lengths and features of the tarsal bones. Morphological traits that suggest leaping include a semi-cylindrical femoral head with moderate posterior expansion of the articular surface, greater trochanter projecting anterior to the femoral shaft, deeper than wide femoral condyles, narrow and deep patellar groove with prominent lateral border, elongated calcaneus, and close aposition of distal tibia and fibula. While Omomys most closely resembles active quadrupedal cheirogaleids like Cheirogaleus and Mirza, leaping must have been an important component of its locomotor repertoire. In this respect, Omomys closely resembles other North American omomyines (notably Hemiacodon), and is significantly more generalized postcranially than European microchoerines (e.g., Microchoerus, Nannopithex, and Necrolemur).