AN ANALYSIS OF THE ARTICULAR SURFACE DISTRIBUTION OF THE FEMORAL-HEADAND ACETABULUM IN ANTHROPOIDS, WITH IMPLICATIONS FOR HIP FUNCTION IN MIOCENE HOMINOIDS

Use of linear techniques to represent complex shapes has constrained m orphological studies of the hip joint, with the result that functional ly significant features have remained unquantified. This study uses a linear least squares sphere fit to the femoral head and acetabular sub chondral bone as a framework for mapping the distribution of articular surface on the joint components of several extant anthropoids. The di stribution of acetabular articular surface is believed to be related t o mobility and the loading environment of the joint. Low dorsal and ca udal lunate surfaces in Pongo permit a wide range of abduction, while an extensive cranial lunate surface implies substantial cranial loadin g. The acetabula of pronograde monkeys has a uniform distribution of a rticular surface; presumably because the hip socket is loaded from cra nial, dorsal and caudal directions. Pan has neither as much cranial lu nate surface as Pongo, nor as much dorsal lunate surface as the monkey s, suggesting a heterogeneous loading environment that may be a conseq uence of Frequently using both orthograde and pronograde postures. The monkeys have a preponderance of articular surface on the anterior asp ect of the Femoral head, reflecting a greater emphasis on adducted, me dially oriented postures and excursions than in Pan. Evidence from the femur, and in the case of Proconsul, the acetabulum, was integrated w ith other data to reconstruct hip mobility and relate it to suspensory behavior in Miocene hominoids. Femoral articular configurations sugge st that most Miocene hominoids had mobile hip joints, which would have facilitated climbing and hindlimb suspension, however, available hume ral material does nor support a similar mobility in the shoulder. The exception to this pattern are the fossil remains from Moroto, which co mbine a monkey-like hip, compatible with quadrupedal hip use, with a b ack that suggests orthograde adaptations. (C) 1996 Academic Press Limi ted