 Almost no sexual dimorphism occurs in this species, although males have more curved dorsal fins with broader bases and greater surface areas.The back of the dolphin is dark grey or black, and the dorsal fin is distinctively two-toned; the leading edge matches the back in colour, but the trailing edge is a much lighter greyish white.The dusky dolphin has a long, light-grey patch on its fore side leading to a short, dark-grey beak.