54.4 Thursday, Jan. 5 The Developmental Basis of 200 Million Year Old Mammal Teeth SMITH, A*; CORFE, I; JERNVALL, J; HAKKINEN, T; GILL, P; Umass, Amherst; Uni of Helsinki, Finland; Uni of Helsinki, Finland; Uni of Helsinki, Finland; Uni of Bristol, UK email@example.com
One difficulty of applying insights from developmental genetics to extinct animals is the limited number of ontogenies preserved in the fossil record. However, fossils do provide information about population variation, which can be investigated using developmental biology. To bridge the gap between development and genetics, we analyzed morphological population variation in a large dental sample of the early triconodont-like mammal Morganucodon from 200 Ma fissure deposits in Glamorgan, Wales. We compared these results with a dentally similar population of the extant ringed seal (Phoca hispida ladogensis) and a virtual population of Morganucodon-shaped teeth generated by a gene-network based computer model of tooth development. Using geometric morphometrics, we found that variation within Phoca and Morganucodon dentitions are generally quite similar. Furthermore, small changes in two of the tooth development model parameters were able to transform a seal tooth into a Morganucodon tooth. Comparison with variation generated by systematically manipulating computer parameters of the developmental model indicates that the same parameters can explain much of the variation in seals and Morganucodon. Finally, Morganucodon teeth show incipient decoupling of the anterior and posterior molar cusps, with less decoupling toward the posterior end of the tooth row. This is a prerequisite for the evolution of tribospheny, which arose 34 Ma before fully tribosphenic teeth first evolved. We infer that the same core genetic pathways present in living seal teeth were already established in the teeth of the earliest mammals, some 200 million years ago, and that this developmental course has required only minor changes in genetic architecture.