Patterns of astragalar fibular facet orientation in extant and fossil primates and their evolutionary implications
Article first published online: 22 JUN 2013
Copyright © 2013 Wiley Periodicals, Inc.
American Journal of Physical Anthropology
Volume 151, Issue 3, pages 420–447, July 2013
How to Cite
Boyer, D. M. and Seiffert, E. R. (2013), Patterns of astragalar fibular facet orientation in extant and fossil primates and their evolutionary implications. Am. J. Phys. Anthropol., 151: 420–447. doi: 10.1002/ajpa.22283
- Issue published online: 22 JUN 2013
- Article first published online: 22 JUN 2013
- Manuscript Accepted: 28 MAR 2013
- Manuscript Received: 7 JAN 2013
- NSF . Grant Number: BCS 1317525 (formerly BCS 1125507) and BCS 1231288 (to D.B. and E.S.)
- American Association of Physical Anthropologists Professional Development Grant (in 2009 to D.B.)
- NSF DDIG . Grant Number: SBE-1028505 (to S.C.)
- ancestral states;
A laterally sloping fibular facet of the astragalus (=talus) has been proposed as one of few osteological synapomorphies of strepsirrhine primates, but the feature has never been comprehensively quantified. We describe a method for calculating fibular facet orientation on digital models of astragali as the angle between the planes of the fibular facet and the lateral tibial facet. We calculated this value in a sample that includes all major extant primate clades, a diversity of Paleogene primates, and nonprimate euarchontans (n = 304). Results show that previous characterization of a divide between extant haplorhines and strepsirrhines is accurate, with little overlap even when individual data points are considered. Fibular facet orientation is conserved in extant strepsirrhines despite major differences in locomotion and body size, while extant anthropoids are more variable (e.g., low values for catarrhines relative to non-callitrichine platyrrhines). Euprimate outgroups exhibit a mosaic of character states with Cynocephalus having a more obtuse strepsirrhine-like facet and sampled treeshrews and plesiadapiforms having more acute haplorhine-like facets. Surprisingly, the earliest species of the adapiform Cantius have steep haplorhine-like facets as well. We used a Bayesian approach to reconstruct the evolution of fibular facet orientation as a continuous character across a supertree of living and extinct primates. Mean estimates for crown Primatomorpha (97.9°), Primates (99.5°), Haplorhini (98.7°), and Strepsirrhini (108.2°) support the hypothesis that the strepsirrhine condition is derived, while lower values for crown Anthropoidea (92.8°) and Catarrhini (88.9°) are derived in the opposite direction. Am J Phys Anthropol 151:420–447, 2013.© 2013 Wiley Periodicals, Inc.