Hominoid humeral torsion : an analysis of its ontogenetic development

Includes bibliographical references (pages [74]-77).This project examined humeral torsion in extant hominoids and humans. Torsion has been used in paleontological studies as an indicator of phylogenetic relationships and locomotor behavior. The angle of torsion and other features of the proximal humerus of juvenile and adult hominoid humeri were measured and compared to assess the degree to which these osteological traits change in the course of development. Statistical analysis revealed that some features of the proximal humerus? torsion and greater tuberosity angle?are ontogenetically stable, remaining relatively constant regardless of age. Other traits, such as lesser tuberosity angle and intertuberosity angle, exhibit more plasticity in the course of development. It has been suggested that a high level of humeral torsion evolved in African apes to accommodate the upper torso and shoulder anatomy of a hylobatid-like hominoid to the mechanical demands of terrestrial quadrupedalism. Examination of extant hominoid torsion values shows that while the evidence for such a correlation is convincing for gorillas, the form-function relationship for chimpanzees is more tenuous because their torsion values are more similar to those of orangutans than to gorillas. Humeral torsion values are relevant to proto-hominid behavior since the torsion values for three early hominid specimens are either very near or within the range for chimpanzees. Therefore, one cannot conclude that the locomotor repertory of proto-hominids did not include terrestrial quadrupedalism.M.A. (Master of Arts