Trabecular Bone Structure in the Mandibular Condyles of Gouging and Nongouging Platyrrhine Primates Timothy M. Ryan, 1 * Matthew Colbert, 2 Richard A. Ketcham, 2 and Christopher J. Vinyard 3 1 Department of Anthropology and Center for Quantitative Imaging, Pennsylvania State University, University Park, Pennsylvania 16802 2 High-Resolution X-Ray CT Facility, Department of Geology, University of Texas, Austin, Texas 78705 3 Department of Anatomy and Neurobiology, NEOUCOM, Rootstown, Ohio 44272 KEY WORDS Jaw functional morphology; biomechanics; callitrichids; marmosets; tamarins ABSTRACT The relationship between mandibular form and biomechanical function is a topic of significant interest to morphologists and paleontologists alike. Sev- eral previous studies have examined the morphology of the mandible in gouging and nongouging primates as a means of understanding the anatomical correlates of this feeding behavior. The goal of the current study was to quantify the trabecular bone structure of the mandibular condyle of gouging and nongouging primates to assess the functional morphology of the jaw in these animals. High-resolution computed tomography scan data were collected from the mandibles of five adult common mar- mosets (Callithrix jacchus), saddle-back tamarins (Saguinus fuscicollis), and squirrel monkeys (Saimiri sciureus), respectively, and various three-dimensional morphometric parameters were measured from the con- dylar trabecular bone. No significant differences were found among the taxa for most trabecular bone struc- tural features. Importantly, no mechanically significant parameters, such as bone volume fraction and degree of anisotropy, were found to vary significantly between gouging and nongouging primates. The lack of signifi- cant differences in mechanically relevant structural parameters among these three platyrrhine taxa may suggest that gouging as a habitual dietary behavior does not involve significantly higher loads on the mandibular condyle than other masticatory behaviors. Alternatively, the similarities in trabecular architecture across these three taxa may indicate that trabecular bone is rela- tively unimportant mechanically in the condyle of these primates and therefore is functionally uninformative. Am J Phys Anthropol 141:583–593, 2010. V V C 2009 Wiley- Liss, Inc. The relationships among diet, mandibular loading, and jaw morphology remain topics of significant interest to both functional morphologists and paleontologists. Resolving the functional significance of mandibular form not only can provide a better understanding of the bio- mechanical underpinnings of particular dietary adapta- tions, but also can be useful in behavioral reconstruc- tions of extinct taxa. Several studies have investigated various aspects of mandibular morphology in gouging and nongouging primates in an attempt to understand the functional morphology of the jaw in tree gougers (Dumont, 1997; Williams et al., 2002; Vinyard et al., 2003; Taylor and Vinyard, 2004; Viguier, 2004; Burrows and Smith, 2005; Vinyard and Ryan, 2006). Although these studies have yielded varying results and interpre- tations, tree-gouging primates appear to be a reasonable model for studying anterior tooth use in primates. One area of mandibular morphology that has received relatively little attention in these previous studies is the internal morphology of the mandibular corpus, symphy- sis, and condyle. Vinyard and Ryan (2006) recently used computed tomography data to compare the cross-sec- tional geometric properties of the mandibular corpus of tree-gouging common marmosets (Callithrix jacchus) to those of nongouging saddleback tamarins (Saguinus fus- cicollis) and squirrel monkeys (Saimiri sciureus). This study found no significant differences in jaw robusticity between the gouging and nongouging species, providing further support for the idea that common marmosets do not generate relatively large bite forces during tree gouging (Vinyard et al., 2003, 2009). The mandibular condyle is subject to a complex set of loading conditions during chewing as it translates and rotates on the glenoid region of the temporal bone (Hylander, 1979; Boyd et al., 1990; Herring and Liu, 2001). The trabecular bone of the condyle transfers these condylar reaction forces to the cortical shell of the ramus during masticatory and ingestive behaviors (Herring and Liu, 2001). In humans and pigs, the condylar trabecular bone is composed of a series of highly anisotropic, sagit- tally oriented plates (Teng and Herring, 1995; Teng et al., 1997; Giesen and van Eijden, 2000). Mechanical and modeling studies of mandibular trabecular bone in these species have demonstrated a close correspondence between the trabecular structure and the apparent me- chanical properties of the condylar trabecular bone (Teng and Herring, 1996; van Eijden et al., 2006). Additionally, comparisons of the structural and mechanical properties Grant sponsor: National Science Foundation (NSF); Grant numbers: BCS-9908847 (to T.M.R.), NSF BCS-094666 (to C.J.V.), BCS-0412153 (to C.J.V.). *Correspondence to: Dr. Timothy M. Ryan, Department of Anthro- pology, 409 Carpenter Building, Pennsylvania State University, Uni- versity Park, PA 16802. E-mail: tmr21@psu.edu Received 7 April 2009; accepted 6 August 2009 DOI 10.1002/ajpa.21178 Published online 16 November 2009 in Wiley InterScience (www.interscience.wiley.com). V V C 2009 WILEY-LISS, INC. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 141:583–593 (2010)