A large hammerhead shark with broad, narrow-blade lateral extensions on the head; width of hammer 26-29% of TL; front margin of head broadly convex, with prominent side indentations, but no central indentation; front teeth blade-like, with 1 point, lower teeth straight, upper teeth oblique, deeply notched on rear side, weakly serrate in adults; rear teeth like front teeth; nostrils short, before eyes on head plane; 5 gill slits, last one over front of pectoral fin; 2 dorsal fins, first moderately large and erect, its rear margin concave; second dorsal and pelvic fins low, rear edge of pelvic ~ straight; anal fin base ~ equal to base of second dorsal fin, its rear margin prominently notched; origin of second dorsal fin slightly behind origin of anal fin; transverse pit above tail base crescent shaped, a pit below tail base; tail fin strongly asymmetrical, notched under tip of top lobe, large lower lobe.
Dark olive to dark grey-brown on back and sides, white below; undersides of pectoral fin tips dusky.
Grows to 500 cm and 400kg; size at birth 50-61cm.
A coastal-pelagic and semi-oceanic hammerhead often sighted near the surface.
Depth: 0-200 m.
Circumglobal in tropical and temperate seas; in the eastern Pacific from California to Chile and the Galapagos and Malpelo. Most common in cooler temperate waters.