1Department of Pathology and Anatomical Sciences, University of Missouri School of Medicine, 2Department of Anthropology, University of Arkansas, 3Hungarian Geological Museum, Geological Institute of Hungary, 4Department of Anthropology, University of Toronto
Thursday 11:15-11:30, Ballroom C
Specialization for below-branch locomotion represents a key transition, or transitions, in the evolution of the Hominidae. Suspensory locomotion has been hypothesized to require substantial hip joint mobility in order to enable abducted limb postures, necessary negotiate the arboreal canopy. If joint mobility is tied to suspensory adaptations, and if hip joint mobility can be reconstructed for fossil taxa, hip joint range of motion estimates would provide a new tool to evaluate locomotor adaptations in fossil apes.
Here we present results of in vivo and in silico measures of hip joint abduction ability in suspensory (Symphalangus, Hylobates, Pongo, Gorilla, Pan, Ateles) and non-suspensory (cercopithecids, Cebus) taxa. Angular abduction at the hip was measured on anesthetized living primates using a goniometer. Pelves and femora of the same taxa were laser scanned and 3D polygonal models were digitally articulated. Maximum hip abduction was modeled using PolyWorks software using strictly-defined morphological criteria for joint movement. These methods were then applied to fossil hominoids Proconsul nyanzae and Rudapithecus hungaricus.
In vivo results demonstrate that suspensory taxa have greater ranges of hip abduction than non-suspensory ones. Estimates based on the in silico models are strongly correlated with the in vivo data, validating the digital models. The early basal hominoid Proconsul had limited hip abduction capabilities similar to non-suspensory quadrupeds, whereas the late Miocene crown hominoid Rudapithecus displays a higher hip abduction capacity. This analysis suggests that there was directional selection for increased hip joint mobility in Rudapithecus.
This study was funded by NSF, Wenner Gren Foundation, LSB Leakey Foundation, NSERC.