Functional myology of the primate head and neck with implications for hominin evolution
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[EMBARGOED UNTIL 5/1/2026] The primate nuchal region has been widely cited as reflecting postural and locomotor behaviors. Postural and locomotor reconstructions of fossil primates, particularly fossil hominins, have relied upon untested hypotheses linking nuchal muscle form and function to bony morphologies. This thesis addresses the gap in knowledge of variation in the primate nuchal musculature and its relationship to positional behaviors through the use of gross cadaveric dissections and in silico visualization and quantification of muscle variables. Nuchal muscle mass is best predicted by body size alone across primates. Additionally, in situ attachment sites of the nuchal musculature are similar among closely related taxa rather than among species with similar positional behaviors. Semisuspensory taxa have more dorsoventrally oriented trapezius muscles when compared to closely related but nonsuspensory taxa. Orthograde primates have less powerful longissimus capitis muscles than pronograde primates do. Further, primates that engage in extreme neck rotation demonstrate differentially oriented and more powerful sternocleidomastoid muscles. These combined results, however, do not translate to overall differences in the moment-generating capacity of the nuchal musculature. The main exception is that primates that engage in extreme neck rotation have larger estimates for moments of lateral flexion of the neck when compared to all other taxa. Overall, this study does not support the idea that nuchal muscle function is driven by positional behaviors alone. It further demonstrates the need to consider muscle morphology and function when using a biomechanical framework to interpret the primate fossil record.
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Ph. D.