Download or read book Ontogeny of the Hominoid Midcarpal Joint and Implications for the Origin of Human Bipedalism written by Tracy Lynne Kivell and published by . This book was released on 2007 with total page 922 pages. Available in PDF, EPUB and Kindle. Book excerpt: This research analyses growth allometry and heterochrony in the ontogeny of the midcarpal joint in extant hominoids and some cercopithecoids to elucidate the functional or phylogenetic bases of the morphological similarities among hominine wrist bones compared to other primates and to clarify the developmental and evolutionary processes that underlie the changes in morphology. This research serves to inform three main goals: (1) qualitative and quantitative description of the developmental morphology of the hominoid carpus; (2) clarify the functional and phylogenetic significance of carpal morphology shared among African apes and humans and the locomotor behaviour of the fossil hominin prebipedal ancestor; (3) clarify functional morphology of Miocene hominoid fossil carpals and reconstruction of positional behaviour. Linear measurements of over 450 subadult and adult carpal specimens, including the scaphoid, lunate, capitate and hamate, of extant hominoids and some cercopithecoids as well as fossil Miocene hominoids were examined. Univariate, bivariate and multivariate analyses of adult morphometric variables revealed significant differences in carpal shape across extant taxa and locomotor groups. Functional interpretation of Miocene hominoid fossils was generally congruent with accepted reconstructions of positional behaviour although some taxa displayed unique morphology for which no modern primate analogue exists. Bivariate and multivariate allometry, supplemented by qualitative descriptions of the subadult carpals, revealed that morphological differences in adults were largely the result of significantly different developmental patterns. Growth allometry and heterochrony did not reveal a clear functional or phylogenetic pattern in degree of ontogenetic variation among taxa for any carpal; extreme and somewhat random ontogenetic variation was the rule, not the exception. However, African apes were consistently more distinct in their developmental patterns, varying more among each other than with other catarrhines, and much of this variation could not be explained by allometric scaling. Humans, in contrast, usually developed in a manner more similar to orangutans and were not strongly autapomorphic as would be predicted by their unique life history. Several carpal features purported to be functionally advantageous for knuckle-walking were not consistently found in adult African apes, their development was not always correlated with increased knuckle-walking behaviour and several features were absent in humans and fossil hominins. Considering morphological similarities between humans and African apes do not appear to follow homologous ontogenetic trajectories, these results fail to support the argument that hominin similarities in wrist morphology are evidence that human bipedalism evolved from a knuckle-walking ancestor. Based on the extreme variation in developmental patterns within African apes to the exclusion of humans, it may be more likely from an ontogenetic perspective to assume that knuckle-walking behaviour evolved independently in Pan and Gorilla.