DISSERTATION RESEARCH: The Evolution of Mammalian Dentition: Insights from fossil synapsid histology

University Of Washington, Seattle WA

Investigators

Abstract

The origin of mammals has long been of interest to scientists because mammals are one of the most diverse groups of animals on the planet. This research investigates how certain complex dental characteristics evolved in the ancestors of modern mammals (therapsids), and thus informs our understanding of the selective forces driving mammalian evolution from their "reptile-like" ancestors. Mammal teeth are considered more complex and specialized than reptiles; however, these assumptions have not fully considered extinct species. As such, the evolution of complex dental traits is not entirely understood, which leaves our understanding of the ecology and evolution of ancient mammals incomplete. Histological data and analyses from this work will be made available to the scientific community, and the data will be useful for systematists interested in the evolution of vertebrates. Public outreach through displays and programs at natural history museums will also occur. The dentition of mammals is unique among living vertebrates, and therapsid fossils have shed light on the evolution of mammalian innovations like a regionalized dentition (heterodonty), multiple tooth roots, and tooth-to-tooth occlusion. While it is relatively straightforward to assess these characters using gross morphology, the evolution of other significant features can only be examined through histological thin sections, and thus remain unknown for many fossil taxa. This research fills this void by using paleohistology and micro-computed tomorgraphy data to determine character states for important dental traits in therapsids. Preliminary data suggest that dental traits once thought exclusive to mammals evolved multiple times in their therapsid forebears. This project also tests for correlative evolution between dental and life history traits along the mammal line as well as in reptilian taxa that have independently evolved these complex traits. The work will provide insight into the selective pressures on the acquisition of mammal innovations.