Mesoplodon

About Mesoplodon

Mesoplodon means "armed with a tooth in the middle of the jaw", and that is very nearly the entire diagnostic basis of the genus. Females and juveniles of most species are close to indistinguishable from one another at sea; adult males erupt a single pair of mandibular teeth whose size, shape and position along the jaw differ enough between species to identify them, and in some cases grow over the upper jaw and physically limit how far the mouth can open.

It is the largest genus of cetaceans by a wide margin and one of the most poorly known groups of large animals anywhere. Several of its species are represented by a few dozen specimens or fewer, most of them strandings; the spade-toothed whale is known from a handful, and was not seen intact until well into this century. New members continue to be added — one resurrected from synonymy in 2014, another split from a familiar species in 2021 — which makes any count of the genus provisional.

What the species share is a life spent hunting squid in deep water far offshore, surfacing briefly and inconspicuously, and consequently going unrecorded. Nearly everything known about their diving and acoustic behaviour comes from tags deployed on a small number of animals in a few well-studied canyons.