Trabecular bone anisotropy and orientation in an Early Pleistocene hominin talus from East Turkana, Kenya Anne Su a, * , Ian J. Wallace b , Masato Nakatsukasa c a Department of Health Sciences, Cleveland State University, Cleveland, OH 44115-2214, USA b Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, Stony Brook, NY 11794, USA c Laboratory of Physical Anthropology, Kyoto University, Kyoto 606-8502, Japan article info Article history: Received 17 September 2012 Accepted 10 March 2013 Available online 16 April 2013 Keywords: Cancellous bone Astragalus Gait Ankle Bone functional adaptation abstract Among the structural properties of trabecular bone, the degree of anisotropy is most often found to separate taxa with different habitual locomotor modes. This study examined the degree of anisotropy, the elongation, and primary orientation of trabecular bone in the KNM-ER 1464 Early Pleistocene hominin talus as compared with extant hominoid taxa. Modern human tali were found to have a pattern of relatively anisotropic and elongated trabeculae on the lateral aspect, which was not found in Pan, Gorilla, Pongo, or KNM-ER 1464. Trabecular anisotropy in the fossil talus most closely resembled that of the African apes except for a region of high anisotropy in the posteromedial talus. The primary orien- tation of trabeculae in the anteromedial region of KNM-ER 1464 was strikingly different from that of the great apes and very similar to that of modern humans in being directed parallel to the talar neck. These results suggest that, relative to that of modern humans, the anteromedial region of the KNM-ER 1464 talus may have transmitted body weight to the midfoot in a similar manner while the lateral aspect may have been subjected to more variable loading conditions. Ó 2013 Elsevier Ltd. All rights reserved. Introduction It is well accepted that Plio-Pleistocene hominins frequently engaged in terrestrial bipedalism, but it remains contentious whether or not their bipedalism was mechanically different from that of modern humans (e.g., Lordkipanidze et al., 2007; Bennett et al., 2009; Haile-Selassie et al., 2012) and/or if they routinely practiced arboreal locomotion (e.g., Stern, 2000; DeSilva, 2009; Green and Alemseged, 2012; Venkataraman et al., 2013). Fossil tali have figured prominently in discussions of early hominin locomo- tor behavior because the shape and arrangement of the articular surfaces of the talus are thought to provide much information about the structure and function of the entire foot (e.g., Wood, 1974; Latimer et al., 1987; DeSilva, 2009). One aspect of talar morphology that may shed additional light on the locomotor behavior of early hominins is the architecture of the trabecular bone contained within the cortical shell. A recent study by DeSilva and Devlin (2012) concluded that trabecular architecture in the hominoid talus has little value in distinguishing among species. Here, we report on data from a large sample of modern human, chimpanzee, gorilla, and orangutan tali, which in contrast does display signifi- cant differences among species that may relate to locomotor dif- ferences and therefore may be useful for inferring locomotor behavior from fossils. In previous comparative studies of trabecular bone structure among primates, the degree of anisotropy (DA), which describes the extent to which trabeculae are aligned into one or more di- rections, has stood out as being most able to distinguish among species whose locomotor repertoires involve different habitual joint kinematics. In species with stereotypic locomotor repertoires with joint motion primarily within a particular plane, trabecular bone tends to display greater anisotropy, whereas in species with more diverse locomotor repertoires involving varied joint kine- matics, trabecular bone tends to display greater isotropy (Fajardo and Müller, 2001; MacLatchy and Müller, 2002; Ryan and Ketcham, 2002; Maga et al., 2006; Griffin et al., 2010; Saparin et al., 2011; but see Carlson et al., 2008). The plate- or rod-like geometry of trabeculae may also be useful for inferring talar loading and locomotor patterns as plate-shaped trabeculae have been shown to develop primarily in joint regions that sustain high mechanical loads, whereas rod-shaped trabeculae tend to develop in regions that experience lower magnitude loads (Ding et al., 2002). In addition to differences in trabecular anisotropy, the * Corresponding author. E-mail addresses: a.su@csuohio.edu (A. Su), ian.wallace@stonybrook.edu (I.J. Wallace), nakatsuk@anthro.zool.kyoto-u.ac.jp (M. Nakatsukasa). Contents lists available at SciVerse ScienceDirect Journal of Human Evolution journal homepage: www.elsevier.com/locate/jhevol 0047-2484/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jhevol.2013.03.003 Journal of Human Evolution 64 (2013) 667e677