04/28/2021
By Joseph Bechara

The Kennedy College of Sciences, Department of Biological Sciences, invites you to attend a master’s thesis defense by Joseph Bechara on “Relationships between craniofacial muscle morphology and dietary specializations across mammal phylogeny."

Candidate Name: Joseph Bechara
Defense Date: Friday, May 14, 2021
Time: 4 to 5 p.m.
Location: Via Zoom
Thesis/Dissertation Title: Relationships between craniofacial muscle morphology and dietary specializations across mammal phylogeny
Advisor: Nicolai Konow, Biological Sciences, University of Massachusetts Lowell
Committee Members:

  • Alison Hamilton, Biological Sciences, University of Massachusetts Lowell
  • David Grossnickle, University of Washington

Abstract:

Mammals form a speciose class with a complex evolutionary history of diversification involving ecological radiations with associated changes in diet and corresponding craniofacial functional morphologies that support food processing. Here, we explore jaw adductor muscle morphological variation among and across North American mammalian dietary groups through physiological cross-sectional area (PCSA)—a predictor of force potential. Carnivores and generalists require jaw force for crushing or subduing prey, whereas herbivore jaws must do work to grind seeds and shear leaves. Accordingly, we hypothesize that carnivores will have greater PCSA of temporalis, and that herbivores will have greater PCSA of masseteric and pterygoid complexes. Additionally, we investigate how the superficial masseter may shift in orientation for varying mechanical needs and hypothesize that as a vertically oriented superficial masseter would increase force production, carnivores will have an increasing superficial masseter line of action angle with respect to the occlusal plane. In support of our hypothesis, we find that carnivores, compared to generalists and herbivores, have a more developed temporalis by about 20% (p < 0.05), while herbivores have more developed pterygoids than generalists and carnivores by about 12% (p < 0.05). In support of our second hypothesis, we observe that carnivores have an increasing superficial masseter line of action angle by an average of about 18 radians (p < 0.05). These data provide evidence for changes across mammals that may have dictated changes in diet based on mechanical requirements of mastication, and thus more broadly highlight how morphology can shape as well as constrain evolutionary ecology.