Family Alopidae – No other sharks in the area have the caudal fin about half the total length.
Unique Characters: Head nearly flat between eyes. Back humped. A deep horizontal groove on nape of each side above gills. Eyes very large, with orbits expanded onto dorsal surface of head. Labial furrows rudimentary. Teeth larger, less than 25 rows in each jaw. First dorsal-fin base closer to pelvic-fin bases than pectoral-fin bases. Pectoral fins broad-tipped; sides above pectoral bases dark, without an extension of the white abdominal area.
Similar Species: Common Thresher Shark Alopias vulpinus. Head strongly arched between eyes. No horizontal groove or an inconspicuous one on nape of each side. Eyes smaller, with orbits not expanded onto dorsal surface of head. Lower labial furrows well developed. Teeth smaller, usually more than 29 rows in each jaw. First dorsal-fin base about equidistant between pectoral- and pelvic-fin bases or closer to pectoral-fin bases. Pectoral fins falcate and narrow-tipped; sides above pectoral bases marked with a white patch extending forward from the abdominal area.