The 89th Annual Meeting of the American Association of Physical Anthropologists (2020)

Is relative entheseal length indicative of locomotor repertoire?


Anthropology, SUNY University at Albany

April 18, 2020 , Platinum Ballroom Add to calendar

Various traits are used to infer locomotor repertoire from the skeleton. This study considers relative length of entheses – muscle and tendon attachment sites – in Ateles geoffroyi, Colobus guereza, Hylobates lar, and Macaca mulatta. Since different locomotor types require varying degrees of usage for separate muscles, we hypothesize that relative entheseal length will differ among species with different locomotor repertoires. This study aims to determine whether relative entheseal length can separate species into locomotor categories: brachiator (H. lar, n=72), intermediate/eclectic (A. geoffroyi, n=9), and quadrupedal (C. guereza, n=27, and M. mulatta, n=42). Specimens are adult and a mixture of captive and wild caught. Relative entheseal lengths were calculated as ln[enthesis length/bone length] for seven entheses (pectoralis major, teres major, deltoid, biceps brachii, brachialis, supinator, gluteus maximus) across four long bones (humerus, radius, ulna, femur). Univariate ANOVA and post hoc Tukey test results show that relative entheseal length does not separate locomotor repertoire as expected, with 0 out of 7 ratio results matching the predicted group separations. However, a linear discriminant function analysis of all seven ratios predicts both locomotor category (97.8% correct classification with leave-one-out cross-validation) and species (95.0% correct classification with cross-validation), driven primarily by relatively short biceps brachii insertions and relatively long deltoid and brachialis insertions in brachiators compared to other locomotor categories. These results suggest that individual relative entheseal lengths may not be accurate indicators of general locomotor signal, but the relationship among relative entheseal lengths across the postcranium may be good predictors of locomotor categories.

Slides/Poster (pdf)