title: Trabecular architecture in the StW 352 fossil hominin calcaneus.
abstract: Australopithecus africanus has been interpreted as having a rigid lateral foot. One mechanism contributing to a rigid foot during push-off in humans is a calcaneocuboid joint (CCJ) with limited dorsiflexion and a "close-packed" talocalcaneal joint (TCJ). In contrast, apes likely have a greater CCJ range of motion and lack a close-packed TCJ. Differences in tarsal arthrokinematics may result in different joint loading environments. In Homo sapiens, we tested the hypothesis that dorsal and plantar CCJ and the TCJ show evidence of predictable habitual loading. In Pan troglodytes, Gorilla gorilla, Gorilla beringei, and Papio ursinus, we tested the hypothesis that only the dorsal CCJ shows evidence of predictable loading. Specifically, we predicted similarity in trabecular properties across the dorsal and plantar CCJ in H. sapiens, but dissimilarity in non-humans. Additionally, we investigated trabecular properties of an A. africanus calcaneus (StW 352) to evaluate joint loading patterns in this hominin and ultimately address the evolution of these properties in H. sapiens. Contrary to predictions, the H. sapiens dorsal CCJ has a significantly higher elongation index, bone volume fraction, trabecular thickness, and trabecular number than the plantar CCJ, while trabecular properties in non-humans do not always differ as predicted between regions. H. sapiens exhibits trabecular morphology indicative of less variable TCJ loading than other groups, having the most anisotropic and rod-like struts oriented in line with predicted principal loads. Multivariate analysis shows that the StW 352 dorsal CCJ matches P. ursinus best, while the plantar CCJ matches G. beringei best and the TCJ matches that of G. gorilla best. Overall patterns suggest that the StW 352 calcaneus experienced more variable loading than H. sapiens, but less variable loading than P. troglodytes, G. gorilla, G. beringei, and P. ursinus, consistent with a large range of foot movements, probably reflecting locomotor kinematics that are unlike those of living humans or apes.
authors.affiliation: Department of Evolutionary Anthropology, Duke University, Box 90383, Durham, NC 27708, USA. Electronic address: angel.zeininger@duke.edu.
authors.forename: Angel
authors.initials: A
authors.lastname: Zeininger
authors.affiliation: Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA; Evolutionary Studies Institute, University of the Witwatersrand, WITS 2050, Johannesburg, South Africa.
authors.forename: Biren A
authors.initials: BA
authors.lastname: Patel
authors.affiliation: Evolutionary Studies Institute, University of the Witwatersrand, WITS 2050, Johannesburg, South Africa; School of Geosciences, University of the Witwatersrand, WITS 2050, Johannesburg, South Africa.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Zipfel
authors.affiliation: Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA; Evolutionary Studies Institute, University of the Witwatersrand, WITS 2050, Johannesburg, South Africa; School of Geosciences, University of the Witwatersrand, WITS 2050, Johannesburg, South Africa; Department of Anthropology, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Kristian J
authors.initials: KJ
authors.lastname: Carlson
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002111:Calcaneus / Q000033:anatomy & histology*; D000071556:Cancellous Bone / Q000033:anatomy & histology*; D005260:Female; D005580:Fossils / Q000033:anatomy & histology*; D015186:Hominidae / Q000033:anatomy & histology* / Q000502:physiology; D006801:Humans; D008124:Locomotion; D008297:Male; D013019:South Africa; D013045:Species Specificity; D013380:Subtalar Joint / Q000033:anatomy & histology* / Q000502:physiology
keywords: Bipedalism; Calcaneocuboid joint; Foot; Midtarsal break; Talocalcaneal joint; Trabecular fabric