Appearance and Anatomy of the Neotropical Otter

Summary

This is an average sized, robustly built otter, very similar in appearance to the other American river otters. The tail can be notably long, forming more than a third of the body length.

Size

The species shows sexual dimorphism - the male is generally 20-25% larger than the female. Larivière seems to have examined smaller animals - he gives weight as less than 12kg, head and body length 36-66cm, tail 37-84cm, but agrees on the dimorphism ratio.

Head and Teeth

The black, hairless rhinarium, or nose pad, the traditional way to distinguish species of New World Otters, is very variable in this species. There seems to be regionalisation of different forms, and the three currently recognised subspecies are characterised as having specific forms, but there is a great deal of variation - all that can be said is that in this species, the rhinarium is smaller than in the North American River Otter to the north and the Southern River Otter to the south of the Neotropical Otter's range.

Van Zyll de Jong considers that the crowns of the teeth in Lontra species is wider than in Lutra species, corresponding to the greater proportion of invertebrates with hard shells in the diet; Aonyx, even more of an invertebrate specialist has even wider molars with reduced cusps.The dental formula is the usual one for otters other than Aonyx cinereus and Enhydra lutris:

I 3/3 C 1/1 P 4/3 M 1/2 = 36

Body

The Neotropical Otter has the classical otter shape. It is robustly built. The females have four nipples low on the abdomen. The male baculum is well-developed, with a small ventral groove shallow proximally, deepening distally, around 72mm long. Like other otters, the animals have a pair of anal scent glands, which produce a liquid which is added to spraint, and is almost certainly conveys information about sex, sexual state and receptivity, and maybe identity.

Tail

The tail of this species is notable for its length in proportion to the body.  The relative length varies but may form a third of the total body length.  It is cylindrical and tapers evenly to the tip.

Legs and Paws

The legs are short, stocky and strong, with the hind legs being longer than the forelegs. The paws are small, wide and strong, with five toes on each, fully webbed to the ends of the digits, hairless underneath and bearing strong claws.

Fur

The fur is short, dense and sleek, with coarse, shiny guard hairs overlaying a soft, woolly undercoat which traps air to keep the animal warm and insulated (otters have no insulating subcutaneous fat layer for insulation). The guard hairs are 12 -14mm long, and the underfur 7 - 9mm long. The colouration is lustrous dark greyish brown dorsally,  becoming paler along the sides of the body, turning paler brown to cream ventrally. The throat and lip area is much
paler, being cream or white in some animals, who may also show individual dark, pale, yellow, cream or white colouration and spotting on the chin and throat; the upper lip, mandible and tip of the muzzle are silvery white to yellowish.

Neotropical Otter