LAMNIFORM SHARK TOOTH MORPHOMETRICS SHOW A SHIFT IN COMMUNITY STRUCTURE OVER THE K/PG MASS EXTINCTION EVENT

Extinct lamniform sharks have left an abundance of disarticulated teeth in the fossil record, but the significance of these to the study of the broader ecosystem is overlooked in the literature. In this study, shark tooth morphology, which in modern taxa corresponds to feeding behaviour and prey choice, is used as a proxy in fossil assemblages to suggest the feeding guilds and community structure present. Tooth morphology was quantified from two lamniform (mackerel shark) assemblages from Morocco, one from each side of the K/Pg boundary, as well as for a selection of morphologically diverse extant taxa. 13 measurements from each tooth were used in Principle Component Analysis (PCA), with results showing a dramatic shift in morphospace. The pre-extinction (Maastrichtian) morphospace has a range smaller than but comparable to that of the extant taxa, while the post-extinction (Danian) morphospace is much reduced, with a considerably smaller range. Teeth tend to be larger and more robust in the Maastrichtian assemblage, overlapping with the Danian assemblage in smaller forms only. Taxonomically there is no overlap, with turnover of all species and all but one genus. These data suggest that this marine ecosystem was highly impacted at apex-predator level by the K/Pg extinction event. A loss of large, robust teeth suggest both a decrease in shark size, and the loss of the prey items (large fish and reptiles) these lamniform morphologies are associated with, though speculations remain tentative until more data are available.