GEOMETRIC MORPHOMETRIC ANALYSIS OF SHARK TEETH OF THE GENUS RHIZOPRIONODON. MODERN TOOTH SHAPE ANALYSIS AND TEST OF ANCESTRAL PREDICTION METHODS BY COMPARISON TO FOSSIL SHAPES

Sharks teeth are extremely common fossil record. Different kinds of sharks have different shaped teeth. These two factors give sharks teeth the potential to provide insight into the evolutionary history of sharks. Unfortunately the variation in tooth shape within an individual shark, between the upper and lower jaw and the various positions around the jaw, frequently confounds the among-species differences.

Fortunately, tooth shape is quantifiable using geometric morphometrics, which measures shape and its covariation with other variables. I used Geometric morphometric techniques to quantify modern patterns of tooth shape variation in teeth of five Rhizoprionodon species and representatives of three closely related genera (Loxodon, Eusphyra, and Sphyrna). Quantification of modern shape variation could then be applied to fossil teeth.

I estimated ancestral tooth shapes by interpolation based on a phylogeny created using molecular data and a Brownian motion model of Evolutionary change. These “estimated ancestral shapes” were then compared to fossil teeth from Rhizoprionodon sp. and Sphyrna spp. to evaluate the accuracy of the estimated “ancestors”.

In general, teeth from each genus could be readily distinguished, but species within Rhizoprionodon could not. Fossil tooth shapes most closely resembled those of modern teeth rather than the estimated ancestral shapes, indicating that the Brownian motion model of shape change provided a poor fit to the actual pattern of evolutionary shape change.