The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


An analysis of the Ardipithecus ramidus pelvis reconstruction using 3D geometric morphometric techniques

NICOLE M. WEBB1,2, WILLIAM E.H. HARCOURT-SMITH1,2,3,4 and HERMAN PONTZER1,2,5.

1Department of Anthropology, The Graduate Center of the City University of New York, CUNY, 2NYCEP, The New York Consortium in Evolutionary Primatology, 3Department of Anthropology, Lehman College, CUNY, 4Department of Paleontology, American Museum of Natural History, 5Department of Anthropology, Hunter College,CUNY

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As a putative hominin, Ardipithecus ramidus’ mosaic postcranium is argued to demarcate the morphological transition from arboreality to bipedal locomotion that occurred following the human-chimp divergence. Its interpretation as a terrestrial biped is largely confined to pelvic features, while its arboreal adaptations are argued to relate to features on the upper limb and the foot. In particular, the forelimb complex has been used to postulate Ar. ramidus as an above branch quadruped that utilized palmigrady while bridging and climbing, with possible functional affinities to early Miocene stem hominoids such as Proconsul.

Here we test these interpretations with a 3D morphometric analysis of the reconstructed Ar. ramidus innominate. 23 homologous pelvic landmarks were collected on a range of extant anthropoid taxa (platyrrhines, hominoids, cercopithecoids) and several fossil hominoid taxa (Proconsul nyanzae, Ar. ramidus, Au. africanus and Au. afarensis). These data were GPA adjusted and subjected to standard multivariate analyses, including PCA.

Our results show that in a number of respects, the ARA-VP-6/500 reconstruction is morphologically distinct from the innominate of H. sapiens and australopiths, and, unlike those taxa, conforms to broad allometric relationships observed in extant monkeys and apes. Overall, the reconstruction most closely resembles the innominates of extant catarrhines and P. nyanzae. However, the posteriorly projecting ischium and unusual mediolateral positioning of the ilium distinguish Ar. ramidus from most other anthropoids, while the relative orientation of the ischium and pubis to the ilium is similar to both cercopithecoids and australopiths. The functional implications of these results are discussed.

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