Bonnethead sharks are well known small coastal sphyrnids that demonstrate the least amount of lateral expansion of their cephalofoil. Bonnetheads from the Pacific were previously described as a separate species or subspecies from Atlantic specimens based upon their different head shapes. Current research on comparative head morphology demonstrates that this difference is strongly supported and that there is an additional sexual dimorphism in head shape at least among specimens from the Atlantic.

Male and female bonnethead sharks do not differ in head morphology between the sexes as embryos and juveniles. As adults, female bonnethead sharks are characterized by a broadly rounded head morphology whereas males possess a distinct bulge along the anterior margin of the cephalofoil. This bulge is formed by the elongation of the rostral cartilages of the males at the onset of sexual maturity and corresponds temporally with the elongation of the clasper cartilages.