Physical data is scant for almost all species on account of the fact that mesoplodons all live far out to sea. For instance it is not known whether females are larger than males. From beached individuals we know that the whales are small, ranged from 4-6m in length and are typically about one 1000-1500kg in weight.

Species typically have a small triangular dorsal fin A dorsal fin is a fin located on the backs of fishes, whales, dolphins and porpoises. Its main purpose is to stabilise the animal against rolling and assist in suddent turns. Some animals have developed dorsal fins with protective functions, such as spines or venom. Many catfish can lock the leading ray of the dorsal fin in an extended position to discourage predation or to wedge themselves into a crevice.

Virtually nothing is known about mesoplodon behaviour as so few have been seen alive. Further their range of behaviours at the surface appears limited to slow swimming. There is usually no surface blow and there have been no reports of a mesoplodon fluking (raising their tail fluke clear of the water on diving).

Longeveity, lactation and gestation data is non-existent.