Item – Theses Canada

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OCLC number
1335714280
Link(s) to full text
LAC copy
Author
Zylstra, Myriam.
Title
Functional morphology of the hominoid forelimb, implications for knuckle-walking and the origin of hominid bipedalism.
Degree
Ph.D. -- University of Toronto, 2000.
Publisher
[Toronto, Ontario] : University of Toronto, 2000
Description
1 online resource
Abstract
Modern African apes, 'Pan' and 'Gorilla ', engage in a unique form of terresrial quadrupedalism called knuckle-walking. They also share with humans a recent evolutionary heritage to the exclusion of Asian apes, and two competing hypotheses have been proposed to explain the origin of human bipedalism. One hypothesis views knuckle-walking as a synapomorphy of chimps and gorillas, having evolved after the divergence of humans from the last common ancestor with African apes. An alternate hypothesis proposes that knuckle-walking was present in the last common ancestor in the lineage leading to African apes and humans, implying that humans evolved from a knuckle-walker. This project has two main objectives. The first is to analyze extant catarrhine forelimb skeletal elements in order to quantify characters that may be functionally linked to knuckle-walking in African apes. The second objective is to determine the presence or absence of these knuckle-walking traits in selected fossil taxa so that inferences regarding their locomotion can be made. Two-dimensional video image analysis is employed to gather data on joint surface areas, angular measures, and joint surface curvatures in three anatomical. The study demonstrates that extant knuckle-walkers are characterized by emphasis on loading across the radial aspect of the wrist, as indicated by larger scaphoid relative to lunate radial surfaces, differences in the pattern of scaling across the proximal carpal row compared to other taxa, and enlarged area of contact at the scaphoid-capitate joint. Profile analysis across metacarpal heads two through five shows that knuckle-walkers are distinguished in the degree of change in curvature from ventral to dorsal aspect of the head, indicating weight-bearing across these joints. In addition, significant weight-bearing is indicated only for metacarpals three and four, despite observed differences between Gorilla and Pan in preferential digit use during knuckle-walking. Finally, the proximal articular surface of the proximal phalanx is medio-laterally expanded in gorillas and chimps. Comparison of a select number of Miocene and Pliocene fossil taxa does not reveal the presence of characters typically found in practicing extant knuckle-walkers.
Other link(s)
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tspace.library.utoronto.ca