Patterns of Serrations on the Teeth of Fossil Great White and Megatoothed Sharks

The evolutionary relationship between the great white shark Carcharodon carcharias and the giant megatoothed shark Carcharocles megalodon is unclear. According to one hypothesis, C. carcharias evolved from C. megalodon in the Pliocene. An alternative hypothesis holds that C. carcharias evolved from the extinct mako shark Isurus hastalis and is distantly related to C. megalodon. To test these hypotheses, we used scanning electron microscopy to examine variations in tooth serrations of C. carcharias and the megatoothed sharks C. angustidens, C. auriculatus and C. megalodon.

The serrations of the Eocene to Pliocene megatoothed sharks display an evolutionary trend. The serration widths decrease and the serrations become more rounded from the Eocene to the Pliocene. Eocene C. auriculatus have serrations with highly variable sizes and shapes (e.g., rounded to angular). Distances between the serration blades of C. auriculatus range from 0.39 mm to 1.64 mm. Oligocene C. angustidens have somewhat rounded and irregular serrations ranging from 0.26 to 1.13 mm. Pliocene C. megalodon have serrations that are highly regular and very rounded and range from 0.50 to 1.12 mm. Carcharocles megalodon have the narrowest range between the maximum and minimum serration blades at 0.62 mm. Other species ranges between serration blades are 0.79 mm (C. carcharias), 0.87 mm (C. angustidens) and 1.25 mm (C. auriculatus), respectively. Carcharodon carcharias serrations do not follow the evolutionary trend of the megatoothed lineage. Their serrations are like those of C. auriculatus (i.e., highly irregular, angular, with widths of 0.49 to 1.25 mm). Because serrations in the Carcharocles lineage first appeared in the Eocene and then evolved to become more rounded and regular, the similarities between the serrations of Pliocene Carcharodon and Eocene Carcharocles indicate that serrations in Carcharodon developed in the Miocene or Pliocene. It is, therefore, unlikely that C. carcharias evolved from C. megalodon.