The evolutionary origin of the great white shark (Carcharodon carcharias) is unclear, with debate centering around two principal hypotheses. The first, based on similarity in tooth shape, claims that C. carcharias originated from a group of extinct mako sharks that includes Isurus hastalis. The second hypothesis, based mostly on cladistic evidence, claims that C. carcharias originated from the same lineage as the giant megatoothed sharks, sharing a close evolutionary ancestor with the extinct Carcharodon megalodon. To distinguish between the two hypotheses we performed several morphometric analyses. In the first analysis, we used Procrustes method and principal components analysis to quantify variation between C. carcharias, I. hastalis, and C. megalodon in four different positions within the dentition. The results indicate no significant difference in tooth shape between C. carcharias and I. hastalis. In the second analysis, correlating tooth size with age, we analyzed teeth from upper anterior and lower anterior positions. For both tooth positions, we show that the growth rate of C. carcharias is more congruent with the growth rate of I. hastalis than that of C. megalodon. Finally, we used scanning electron microscopy to show that the tooth serrations of C. carcharias are distinct from those of the megatooths and more similar in size to those of slightly serrated mako teeth. Taken together, these results indicate that C. carcharias originated from an extinct group of mako sharks and not from the megatoothed sharks.
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Vol. 26 • No. 4