TOOTH MORPHOLOGY PROVIDES EVIDENCE OF ANCESTRAL MEGALODON LINEAGE

The phenetic relationships within the mega-toothed shark evolutionary lineage that culminates in C. megalodon are unclear. Previously noted patterns by collectors between several predominant taxa have elicited numerous hypotheses, however, few analytical approaches have been applied to test the relationships therein.

Geometric morphometrics was used to describe overall tooth shape (upper anterior jaw) of the extinct mega toothed sharks and resulting axes were combined in a cluster analysis to indicate phenetic relationships among taxa. In addition, counts of serrations and variability in serration spacing / height were included to describe taxa. The primary morphological gradients retrieved included gradations between individuals based on root lobe and bourlette width as well as blade and cusplet width.

Taxa classified as C. appendiculata, O. obliquus, C. aksuaticus, C. auriculatus, C. sokolovi, C. anguistidens, C. chubatensis, and C. megalodon tended to exhibit increasingly wide blade and root widths with an increasingly reduced cusplet presence, respectively. This taxa gradation was also typified by the appearance of and gradual reduction of serration counts and variation in appearance.

Inclusion of overall shape gradients and serration measurements in neighbor-joining cluster analysis indicated closest relationships between C. chubutensis and C. megalodon taxa and C. appendiculata and O. obliquus taxa. Future research will repeat the above analysis using additional tooth datasets from lower anterior, upper lateral, and lower lateral tooth specimens.