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

Estimating body mass in the Theropithecus oswaldi lineage using long bone ends


Department of Anthropology, University of Oregon

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Theropithecus oswaldi was a terrestrial gramnivorous cercopithecine monkey known from the Pliocene and Pleistocene of Africa. Using craniodental measures, many authors have noted a trend of increasing size through time. A lack of relatively complete elements has hampered evaluation of this trend using postcrania. This study aims to estimate body mass in T.oswaldi over approximately 3.5 Myr using proximal and distal fragments of the long bones, which are relatively abundant at fossil sites. Of the 15 predictor variables assessed by Eller et al. (2011) on a large sample of extant cercopithecid long bone ends, the five best performing (R2 above 0.90, within 80% of actual value more than 75% of the time, and mean prediction error below 15%) were used to estimate mass: proximal humeral anteroposterior diameter, humeral biepicondylar breadth, femoral head anteroposterior diameter, femoral bicondylar breadth, and tibial bicondylar breadth. These were analyzed on 172 humeri, radii, femora, and tibiae attributed to T. oswaldi. Fossil data is from seven sites in Ethiopia, Kenya, and Tanzania and samples 23 time horizons between 3.5 to less than 0.5 Ma. Results indicate a clear increase in size through time, with early samples close in size to extant baboons (e.g. Hadar, Denen Dora, female range 8 – 17 Kg; male range 19 – 28 Kg) and the younger populations (e.g. Olorgesailie, female range 33 – 58 Kg; male range 67 – 102 Kg) represent the largest cercopithecoids known. Our results overlap the values found by Delson et al. (2000) based on other postcranial, cranial, and dental data.

This study of was funded by the Leakey Foundation (SF,EG), the Wenner-Gren Foundation (SF), Geological Society of America (EG), the Paleontological Society (EG), the National Science Foundation (EG), and the University of Oregon (SF,EG).

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