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Morphological Integration in the Mandibles of Living Reptiles and Fossil Synapsids

Living mammals have a unique mandible (lower jaw) morphology compared to other tetrapods. In mammals, each side of the mandible is formed by a single bone, the dentary, whereas all other tetrapods possess a series of postdentary bones in addition to the dentary. The reason for this difference is the fact that the postdentary bones of the ancestors of mammals have been reduced in size, detached from the jaw, and incorporated in to the hearing system of mammals. However, mammals are a subgroup of a larger group called Synapsida, and many nonmammalian synapsids possess large postdentary bones that resemble those of other tetrapods.

Research Methods and Techniques: The REU participant will collect geometric morphometric data on the jaws of a wide range of living reptiles, all of which have post dentary bones, and will examine whether all of the bones of the mandible form a single integrated unit or if subgroups of bones form distinct modules. We will then apply similar methods to the jaws of nonmammalian synapsids with postdentary bones to determine whether they show similar patterns of modularity/integration or if there are differences that may help to explain why the ancestors of synapsids were able to co-opt their postdentary bones for hearing.

Advisor: Dr. Kenneth D. Angielczyk (Curator, Geology)