Heritage Cases

My dissertation focuses on how mammal dentition arose deep in our evolutionary history from a novel perspective. I am looking at dental traits that are only discernable in fossil animals by looking at the microstructure of their hard tissues. One of the traits I am interested in mapping throughout synapsid evolution is mode of tooth attachment. Mammals are thought to have acquired a unique soft tissue ligament to anchor their teeth, however there is a growing body of evidence that this tissue and tooth attachment strategy has appeared multiple independent times in evolutionary history in an array of tetrapods (e.g. Jasinoski and Chinsamy, 2012; LeBlanc et al., 2016). Since we now recognize this trait is not unique to mammals, the selective pressures resulting in the acquisition of this trait is not unique to mammals. My dissertation focuses on examining macroevolutionary trends of tooth attachment in fossil synapsids to test hypotheses about possible reasons why so many animals have independently acquired this tooth attachment strategy. Of particular interest among synapsids are dinocephalians. Boonstra (1962) initially hypothesized that the derived group of dinocephalians, tapinocephalids, had a soft tissue tooth attachment because their fossil jaws were often recovered without teeth. I am testing this original hypothesis and examining whether or not this character state was ancestral for the larger dinocephalian group. Thus, I am collecting histological data on tapinocephalids and their more basal dinocephalians relatives, anteosaurs and titanosuchians to 1) establish character states each clade and then 2) determine whether this soft tissue attachment was independently acquired in tapinocephalids, meaning that this trait appeared nearly 100 million years earlier in synapsid history than previously thought. I have preliminary evidence from tapinocephalids collected by my advisor from Tanzania and Zambia that suggest tapinocephalids did have a soft tissue tooth attachment. However, the specimens I have thin sectioned did not have teeth in the jaws. Boonstra has previously cut up several tapinocephalid, titanosuchian, and anteosaurus specimens jaws with teeth in situ. I am requesting to finish these sections into true thin sections that will allow me and future researchers to access much more data in the microstructural details of these jaws.