The Narrow Niche hypothesis: Gray squirrels shed new light on primate origins
Article first published online: 4 JAN 2011
Copyright © 2011 Wiley-Liss, Inc.
American Journal of Physical Anthropology
Volume 144, Issue 4, pages 617–624, April 2011
How to Cite
Orkin, J. D. and Pontzer, H. (2011), The Narrow Niche hypothesis: Gray squirrels shed new light on primate origins. Am. J. Phys. Anthropol., 144: 617–624. doi: 10.1002/ajpa.21450
- Issue published online: 14 MAR 2011
- Article first published online: 4 JAN 2011
- Manuscript Accepted: 5 OCT 2010
- Manuscript Received: 29 DEC 2009
- primate origins;
- Sciurius carolinensis;
Current hypotheses for primate origins propose that nails and primate-like grasping hands and feet were important early adaptations for feeding in fine branches. Comparative research in this area has focused on instances of convergence in extant animals, showing that species with primate-like morphology feed predominantly from terminal branches. Little has been done to test whether animals without primate-like morphology engage in similar behavior. We tested the fine-branch niche hypothesis for primate origins by observing branch use in Eastern gray squirrels, Sciurus carolinensis, a species lacking primate grasping adaptations that has been understudied in the context of primate origins. We hypothesized that because gray squirrels lack primate-like grasping adaptations, they would avoid feeding and foraging in terminal branches. Instantaneous focal animal sampling was used to examine the locomotor and postural behaviors used while feeding and foraging. Our results demonstrate habitual and effective usage of terminal branches by gray squirrels while feeding and foraging, primarily on tree seeds (e.g., oak, maple, and elm). Discriminant function analysis indicates that gray squirrels feed and forage like primates, unlike some other tree squirrel species. Given the absence of primate-like features in gray squirrels, we suggest that although selection for fine-branch foraging may be a necessary condition for primate origins, it is not sufficient. We propose an alternative model of primate origins. The Narrow Niche hypothesis suggests that the primate morphological suite evolved not only from selection pressure for fine branch use, but also from a lack of engagement in other activities. Am J Phys Anthropol, 2011. © 2011 Wiley-Liss, Inc.