Bonnethead began with a taxon that had a highly pronounced cephalofoil (most likely that similar to the winghead shark, "Eusphyra blochii"), and was later modified through selective pressures. Thus, judging by their smaller cephalofoils, bonnethead sharks are the more recent developments of a 25-million-year evolutionary process. This species occurs off the American coast, in regions where the water is usually warmer than . It ranges from New England, where it is rare, to the Gulf of Mexico and Brazil, and from southern California to Ecuador. During the summer, it is common in the inshore waters of the Carolinas and Georgia; in
Scalloped bonnethead mallet-shaped head, called a cephalofoil, is moderately wide (24-29% of total length) and elongated lengthwise. The front margin is broadly arched, with shallow lateral and medial indentations, and no prenarial grooves. The mouth is small and strongly arched. The anal fin is long and has a nearly straight rear margin. Its coloration is gray above and white below, with no prominent fin markings. The similar scoophead ("Sphyrna media") can be distinguished by a shorter snout, a broader mouth, and a deeply concave anal fin margin. Like other hammerheads, the scalloped bonnethead is viviparous, with presumably two pups per litter. The