The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)


The thumb of Homo floresiensis: first comparative analyses of the proximal and distal pollical phalanges from Liang Bua

ISABELLE CREVECOEUR1, MATTHEW W. TOCHERI2, ROKUS DUE AWE3, CALEY M. ORR4, STEVIE CARNATION4 and WILLIAM L. JUNGERS4.

1PACEA UMR-5199, CNRS, Université Bordeaux 1, 2Human Origins Program, Department of Anthropology, National Museum of Natural History, Smithsonian Institution, 3National Research and Development Center for Archaeology, Jakarta, Indonesia, 4Department of Anatomical Sciences, Stony Brook University Medical Center

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Only one thumb bone, a distal pollical phalanx (LB1-55), has thus far been described for Homo floresiensis. Although LB10 was initially identified as a hallucal proximal phalanx in part because of its thick ovoid diaphysis, newly identified hallucal proximal phalanges of Homo floresiensis indicate that LB10 is a pollical proximal phalanx. Here we compare the thumb phalangeal morphology of Homo floresiensis with that of a large sample of living apes and extant and fossil hominins. Our univariate and multivariate results show that both Homo floresiensis pollical phalanges are characterized by proportionally thicker midshafts and smaller articular surfaces than in the modern human sample. LB10 also exhibits significantly greater proximal height compared with modern humans and in this respect is more similar to the relatively robust proximal phalanges of gorillas. Overall, the morphology of LB10 is more human-like than is the proximal pollical phalanx of Australopithecus afarensis (A.L. 333-69). LB1-55 is characterized by a well-marked insertion of the flexor pollicis longus and a modern human-like apical tuft shape, and differs from the modern human sample mostly in size. Using size-adjusted variables, LB1-55 falls within the observed modern human variation, being characterized by a small proximal articular surface and a thick midshaft. In these respects, LB1-55 differs considerably from living apes and other fossil hominins. The combination of characteristics seen in the Homo floresiensis thumb phalanges raises important questions about the biomechanical implications of small articular surfaces associated with a strongly reinforced midshaft, and about the evolution of thumb morphology in hominins.

This research was supported in part by the Smithsonian Scholarly Studies Program, the French Centre National de la Recherche Scientifique and the Australian Research Council

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