The Amazonian manatee (Trichechus inunguis) is a species of manatee of the order Sirenia, which is shares with the marine dugong. It is found living in the freshwater habitats of the Amazon Basin in Brazil, Peru, Colombia, Ecuador, Guyana, and Venezuela. Its colour is grey, but sometimes appears to be a brownish grey. It has thick, wrinkled skin, and is almost hairless, but has "whiskers" around its mouths. It lacks significant predation, other than being occasionally hunted by humans.
An almost unique feature (amongst mammals) of the manatee is the constant replacement of molar teeth; new teeth enter at the back of the jaw and replace old and worn teeth at the front. The order's closest relatives, the elephants, also have teeth that get replaced, but have only a limited set of these replacement teeth.
The Amazonian manatee is the second-smallest species of manatee after the dwarf manatee. It may reach a length of 2.8 m (9.2 ft). Females are typically larger than males, and can weigh 360 to 540 kg (790 to 1,200 lb). Unlike the West Indian manatee, it lacks nails on the end of most flippers.
Recently, a closely related, but far smaller species, the dwarf manatee (Trichechus pygmaeus), has been described from Brazil by Dr. Marc van Roosmalen. Called the peixe-boi anão in Brazilian Portuguese, it is about 130 cm (4.3 ft) long and lives in fast-flowing streams. Its validity has later been questioned, with some believing it to be an immature Amazonian manatee.