The 85th Annual Meeting of the American Association of Physical Anthropologists (2016)


Relative length of the immature Homo naledi tibia U.W. 101-1070: evidence for elongation of the leg

CHRISTOPHER S. WALKER1,2,3, JEREMY M. DESILVA3,4, TRENTON W. HOLLIDAY3,5, DAMIANO MARCHI3,6, HEATHER M. GARVIN3,7,8, ZACHARY COFRAN3,9, JOHN HAWKS10,3, LEE R. BERGER11,3 and STEVEN E. CHURCHILL2,3.

1College of Veterinary Medicine, North Carolina State University, 2Department of Evolutionary Anthropology, Duke University, 3Evolutionary Studies Institute, University of the Witwatersrand, 4Department of Anthropology, Dartmouth College, 5Department of Anthropology, Tulane University, 6Department of Biology, University of Pisa, 7Department of Anthropology/Archaeology, Mercyhurst University, 8Department of Applied Forensic Sciences, Mercyhurst University, 9School of Humanities and Social Sciences, Nazarbayev University, 10Department of Anthropology, University of Wisconsin-Madison, 11School of Geosciences, University of the Witwatersrand

April 16, 2016 10:30, Imperial Ballroom A Add to calendar

It is largely held that the transition from Australopithecus to the genus Homo involved a shift in overall body proportions, including a relative lengthening of the lower limb, though the degree to which hominin limb proportions changed and the proximate causes thereof remain contentious topics. The overall poor preservation of most articular surfaces and predominately fragmentary diaphyses in the mature Dinaledi lower limb long bone sample preclude a definitive assessment of lower limb proportions based on this material alone. The U.W. 101-1070 immature tibia is the most complete H. naledi lower limb element recovered to date, measuring 278 mm from the eminence of the tibial spines to the distal extent of the medial malleolus, and preserving nearly the entire medial condyle. To assess proportions, we evaluated tibia medial condylar dimensions relative to tibia maximum length in U.W. 101-1070, other fossil hominin tibiae, and an ontogenetic sample of humans, chimpanzees, and gorillas. Results indicate that the U.W. 101-1070 tibia is very long relative to joint size – markedly differing from all extant species and comparative fossil hominin tibiae. The combination of an exceptionally small tibial articular surface (like many australopiths) and moderately long tibia, in H. naledi, appears autapomorphic in the hominin fossil record. Though the specific implications of this finding are partially dependent on the geological age and phylogenetic position of H. naledi, U.W. 101-1070 provides an example of bone length/joint size decoupling relative to the human pattern.