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


Allometry of calcaneal elongation in euprimate origins

DOUG M. BOYER1,2,3, JUSTIN T. GLADMAN2,3 and JONATHAN I. BLOCH4.

1Department of Evolutionary Anthropology, Duke University, 2Department of Anthropology, CUNY Graduate Center, 3New York Consortium of Evolutionary Anthropology, (NYCEP), 4Department of Vertebrate Paleontology, Florida Museum of Natural History, University of Florida

Thursday 8:45-9:00, Ballroom C Add to calendar

Acrobatic leaping is often associated with the origin and subsequent radiation of Euprimates based on its observed frequency in extant primates and inferred frequency in fossils. Hypothesized skeletal correlates include elongated hind limb segments, particularly the calcaneus that may aid leaping by allowing for increased rates and durations of propulsive acceleration at takeoff. Testing this relationship is complicated by body size differences and associated allometric affects. Alternatively, moderate calcaneal elongation of many euprimates may primarily relate to grasping specializations that necessitate a tarsifulcrumating foot.

We re-assess allometric constraints on, and functional significance of, calcaneal elongation using Phylogenetic Generalized Least Squares for regression and ancestral state reconstruction (ASR). Results show that among all primates, logged ratios of distal- to total-calcaneal length are inversely correlated with logged calcaneal body mass proxies. A line with similar coefficients is independently defined by early Eocene Teilhardina, Cantius, and Notharctus together. If calcaneal elongation is interpreted in the context of this allometric relationship, then relatively elongate calcanea in omomyids could be explained by small body size relative to that of adapids, rather than by differences in leaping proclivity. In contrast, galagids, tarsiers, and most lemuriforms deviate from the line defined by Eocene forms with large positive residuals, meaning another factor besides body size (possibly leaping proclivity) may be invoked. Small residuals of extant Cheirogaleous reflect a good match with Eocene taxa. ASR shows non-allometric increases in elongation near the origin of Euprimates, possibly associated with the development of hallucal-grasping or a combination of grasping and leaping.

Research was supported by an NSF grant to DMB (NSF BCS 1125507)

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