USING QUANTITATIVE MORPHOMETRICS AND OUTLINE ANALYSIS TO DELINEATE ONTOGENETIC HETERODONTY IN RECENT AND FOSSIL TAXA OF WHITE SHARKS (FAMILY LAMNIDAE)

Many sharks exhibit ontogenetic heterodonty, expressing various dental morphologies at different life stages. Accurately identifying these ontogenetic patterns would allow for life stage to be estimated from isolated fossil or Recent teeth, and potentially aid in re-evaluating dubiously erected fossil shark taxa. We use quantitative techniques to investigate these patterns in lamnid sharks, in which developmental stages are often demarcated by such dental characters as the size and number of serrations, broadness of the main cusp, and the presence or absence of lateral cusplets.

Complications can arise when attempting to identify these qualitative characters in fossil specimens – serrations and cusplets may not be present due to wear or damage, and the shape and overall condition of isolated teeth may lead to incorrect identifications. In addition, many sharks, including lamnids, exhibit multiple forms of heterodonty, such as anterior-lateral heterodonty, that must be accounted for in studying tooth variation. To more rigorously address heterodonty in sharks, we use landmark-based geometric morphometrics and outline analysis via Elliptical Fourier Analysis (EFA), which allows us to capture the range of tooth shapes expressed by white sharks at various ontogenetic life stages, quantify the differences between those tooth shapes, and control for the effect that anterior-lateral heterodonty has on tooth shape.

We have applied these techniques to a lamnid dental material dataset. We digitized and analyzed a series of complete jaw sets from the Great White Shark, Carcharodon carcharias, a member of the family Lamnidae, comparing jaw sets collected from sharks of various developmental stages (neonate, juvenile, and adult). We divided the teeth into datasets based on position in the jaw (anterior, lateral, posterior) to account for the effect of anterior-lateral heterodonty. We applied these same techniques to a sample of isolated fossil white shark teeth and found that the fossil sample set largely reflected the same degree of ontogenetic shape variation as the series of Recent jaws. We then compared the C. carcharias dataset to digitized teeth from other recent and fossil lamnids, including Isurus and Lamna, to determine overall quantifiable patterns in ontogenetic heterodonty across the family Lamnidae.