title: Forearm articular proportions and the antebrachial index in Homo sapiens, Australopithecus afarensis and the great apes.
abstract: When hominin bipedality evolved, the forearms were free to adopt nonlocomotor tasks which may have resulted in changes to the articular surfaces of the ulna and the relative lengths of the forearm bones. Similarly, sex differences in forearm proportions may be more likely to emerge in bipeds than in the great apes given the locomotor constraints in Gorilla, Pan and Pongo. To test these assumptions, ulnar articular proportions and the antebrachial index (radius length/ulna length) in Homo sapiens (n=51), Gorilla gorilla (n=88), Pan troglodytes (n=49), Pongo pygmaeus (n=36) and Australopithecus afarensis A.L. 288-1 and A.L. 438-1 are compared. Intercept-adjusted ratios are used to control for size and minimize the effects of allometry. Canonical scores axes show that the proximally broad and elongated trochlear notch with respect to size in H. sapiens and A. afarensis is largely distinct from G. gorilla, P. troglodytes and P. pygmaeus. A cluster analysis of scaled ulnar articular dimensions groups H. sapiens males with A.L. 438-1 ulna length estimates, while one A.L. 288-1 ulna length estimate groups with Pan and another clusters most closely with H. sapiens, G. gorilla and A.L. 438-1. The relatively low antebrachial index characterizing H. sapiens and non-outlier estimates of A.L. 288-1 and A.L. 438-1 differs from those of the great apes. Unique sex differences in H. sapiens suggest a link between bipedality and forearm functional morphology.
authors.affiliation: Department of Anthropology, Georgia State University, 33 Gilmer Street, Atlanta, GA 30303, USA. Electronic address: Frankwilliams@gsu.edu.
authors.forename: Frank L'Engle
authors.initials: FL
authors.lastname: Williams
authors.affiliation: Department of Anthropology, Texas State University, 601 University Drive, San Marcos, TX 78666, USA.
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Cunningham
authors.affiliation: Department of Applied Physics, Institute of Physics, University of São Paulo, Rua do Matão Travessa R Nr. 187, CEP 05508-090 Cidade Universitária, São Paulo, SP, Brazil.
authors.forename: Lia Q
authors.initials: LQ
authors.lastname: Amaral
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001696:Biomechanical Phenomena; D016000:Cluster Analysis; D005260:Female; D005542:Forearm / Q000033:anatomy & histology* / Q000502:physiology; D005580:Fossils / Q000033:anatomy & histology; D006071:Gorilla gorilla / Q000033:anatomy & histology / Q000502:physiology; D015186:Hominidae / Q000033:anatomy & histology* / Q000502:physiology; D006801:Humans; D008297:Male; D002679:Pan troglodytes / Q000033:anatomy & histology / Q000502:physiology; D011148:Pongo pygmaeus / Q000033:anatomy & histology / Q000502:physiology; D011884:Radius / Q000033:anatomy & histology; D012727:Sex Characteristics; D013045:Species Specificity; D014457:Ulna / Q000033:anatomy & histology