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


Differences between eastern and western gorillas in the forelimb and hindlimb skeletons

REBECCA JABBOUR.

Department of Biology, Saint Mary’s College of California

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Gorilla systematics has received increased attention over the past two decades. Studies of geographic variation in DNA, skulls, and teeth have led to new taxonomic proposals, such as recognition of two species, Gorilla gorilla (western) and G. beringei (eastern), and subspecies-level recognition of Cross River gorillas (G.g. diehli). Using a geographically diverse sample, this study tests the hypothesis that the split between eastern and western gorillas is reflected in their forelimb and hindlimb skeletons.

Forty-three linear measurements were collected from the humerus, radius, third metacarpal, femur, tibia, calcaneus, first metatarsal, third metatarsal, and third proximal hand and foot phalanges of 266 adult gorillas. Comparisons of means and PCAs confirm clear separation between eastern and western gorillas. In particular, eastern gorillas have smaller hands and feet than western gorillas, and the eastern subspecies G.b. beringei and G.b. graueri each have smaller hands and feet than G.g. gorilla. Previous authors noted shorter fingers in G.b. beringei compared to G.g. gorilla and suggested this to be an adaptation to montane habitats, providing advantages for terrestrial locomotion or heat retention. Small hands and feet may reflect the evolutionary importance of montane adaptations in all eastern gorillas.

These results support the two-species proposal; however, the single available skeleton of the altitudinally-variable G.g. diehli with hands and feet suggests a twist. Its hand and foot bones are unusually small for G. gorilla. Perhaps a larger G.g. diehli sample would show that the lowland-dwelling G.g. gorilla is unique among Gorilla subspecies in having large hands and feet.

This study was supported by The Wenner-Gren Foundation, The Leakey Foundation, Sigma Xi, City University of New York, and New York Consortium in Evolutionary Primatology.

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