MORPHOLOGICAL VARIANCE IN THE BIOGEOGRAPHICAL DISTRIBUTION OF LAMNIDAE SPECIES C. MEGALODON AND C. CARCHARIAS

The extinct and modern Lamniform species, C. megalodon and C. carcharias, are some of the largest and most geographically widespread apex predators in the fossil record. However, little is known regarding the mechanism which undergirds this cosmopolitan distribution. The objective of this study was to assess whether variation in tooth morphology coincides with geography. Detecting this relationship could provide a potential mechanism that links populations to functional relationships inherent in tooth morphology. This would offer a plausible explanation invoking population level dietary plasticity or selection as potential mechanisms that facilitated their widespread occurrences. Conversely, not detecting this difference could have both large scale population or selection implications. In this study, we used specimens housed in museum collections to assess morphological variation in upper teeth (lingual view) from anterior positions from several locations around the globe spanning modern day continents of North and South America. We used geometric morphometric techniques to describe tooth morphology and specifically tested for geographic differences in each species tooth shape by extracting morphometric axes from relative warp analyses and subjecting these axes to ANOVA tests using continent of collection as the grouping variable. Teeth from C. megalodon were not found to significantly covary by geographic region, with specimens from South America tending to overlap in shape with those from North America. Similarly, C. carcharias specimens were not found to covary with region, with specimens from South America tending to exhibit similar shapes compared with those from North America. This overlap in geographic variation of tooth shape suggests a lack of selection contingent on space as well as a potential larger population that could dilute any geographic signal as a result of their distribution. These results suggest the need for additional studies dealing specifically with ecomorphological relationships as well as testing this hypothesis on multiple other spatial scales as well as with other tooth positions.