TRACING THE ANCESTRY OF THE GREAT WHITE SHARK USING MORPHOMETRIC ANALYSES OF FOSSIL TEETH
The second hypothesis, based mostly on cladistic evidence, claims that C. carcharias originated from the same lineage as the giant mega-toothed sharks, sharing a close evolutionary ancestor with the extinct Carcharodon megalodon. Proponents of this hypothesis argue that similarity in tooth shape between C. carcharias and I. hastalis results from convergent evolution.
To empirically distinguish between the two hypotheses we performed the following morphometric analyses. In the first analysis, correlating tooth size with age, we analyzed teeth from four key positions in the mouth; upper anterior, upper lateral, lower anterior, and lower lateral. For each tooth position we show that the growth rate of C. carcharias is more congruent with the growth rate of I. hastalis than that of C. megalodon. In the second analysis, we use Procrustes method and principal components analysis (PCA) in order to quantitatively determine the amount of variation between C. carcharias, I. hastalis, and C. megalodon. Again, we analyzed teeth from the same four key positions. Here, the resulting analysis indicates that variation between C. carcharias and I. hastalis is not significant.
In both analyses, tooth shape of I. hastalis correlated strongly with tooth shape of C. carcharias in all four key positions, while tooth shape of C. megalodon showed little similarity to that of C. carcharias. This strong correlation among teeth in all four positions leads us to reject the convergent evolution hypothesis and support I. hastalis as a predecessor to C. carcharias.