The strap-toothed whale (Mesoplodon layardii), also known as the Layard's beaked whale or the long-toothed whaleis a large mesoplodont with some of the most bizarre teeth of any mammal. The common and scientific name was given in honor of Edgar Leopold Layard, the curator of the South African Museum who prepared drawings of a skull and sent them to the British taxonomist John Edward Gray, who described the species in 1865.
The overall body shape of the strap-toothed whale is fairly typical for a mesoplodont, except for the large size. Male specimens have large and peculiar teeth even for the genus; the teeth emerge from the lower jaw and grow upward and back at a 45 degree angle to encircle the upper jaw and nearly close it. These teeth can sometimes grow to over 30 centimetres (0.98 ft) in length. The teeth have dorsally projecting denticles, and are apparently used for fighting. Barnacles are frequently found on the teeth, as well. Why the species would grow teeth that severely cut back on the size of prey it can consume is uncertain. The melon is somewhat bulbous, and blends into the beak shortly before the strap teeth. The beak itself is fairly long, with a relatively straight mouthline. The coloration of this species is also unusual for a mesoplodont, since it is rather bold; most of the body is black except for a white areas on the front of the beak, the throat, an area behind the head in a shape reminiscent of a cape, and near the genitals. Juveniles do not have this coloration and are typically countershaded, dark above and light below.