Functional aspects of metatarsal head shape in humans, apes, and Old World monkeys.
Modern human metatarsal heads are typically described as "dorsally domed," mediolaterally wide, and dorsally flat. Despite the apparent functional importance of these features in forefoot stability during bipedalism, the distinctiveness of this morphology has not been quantitatively evaluated within a broad comparative framework. In order to use these features to reconstruct fossil hominin locomotor behaviors with any confidence, their connection to human bipedalism should be validated through a comparative analysis of other primates with different locomotor behaviors and foot postures, including species with biomechanical demands potentially similar to those of bipedalism (e.g., terrestrial digitigrady). This study explores shape variation in the distal metatarsus among humans and other extant catarrhines using three-dimensional geometric morphometrics (3 DGM). Shape differences among species in metatarsal head morphology are well captured by the first two principal components of Procrustes shape coordinates, and these two components summarize most of the variance related to "dorsal doming" and "dorsal expansion." Multivariate statistical tests reveal significant differences among clades in overall shape, and humans are reliably distinguishable from other species by aspects of shape related to a greater degree of dorsal doming. Within quadrupeds, terrestrial species also trend toward more domed metatarsal heads, but not to the extent seen in humans. Certain aspects of distal metatarsus shape are likely related to habitual dorsiflexion of the metatarsophalangeal joints, but the total morphological pattern seen in humans is distinct. These comparative results indicate that this geometric morphometric approach is useful to characterize the complexity of metatarsal head morphology and will help clarify its relationship with function in fossil primates, including early hominins.
Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, Stony Brook, NY 11794, USA. Electronic address: pedro.fernandez@stonybrook.edu.
Peter J
PJ
Fernández
Center for the Advanced Study of Human Paleobiology, Department of Anthropology, The George Washington University, Washington, DC 20052, USA; Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY 11794, USA; Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Barcelona 08193, Spain; NYCEP Morphometrics Group, USA.
Sergio
S
Almécija
Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
Biren A
BA
Patel
Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, CO 80045, USA.
Caley M
CM
Orr
Department of Anthropology, Lakehead University, Thunder Bay, Ontario P7B 5E1, Canada; Human Origins Program, Department of Anthropology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA.
Matthew W
MW
Tocheri
Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY 11794, USA.
William L
WL
Jungers
D000818:Animals; D005075:Biological Evolution; D002520:Cercopithecidae / Q000033:anatomy & histology* / Q000502:physiology*; D005580:Fossils; D015186:Hominidae / Q000033:anatomy & histology* / Q000502:physiology*; D006801:Humans; D008682:Metatarsal Bones / Q000033:anatomy & histology* / Q000502:physiology*; D016138:Walking / Q000502:physiology*
3D geometric morphometrics; Bipedalism; Dorsal doming; Functional morphology; Metatarsals