In historical time in Brazil large fish-eating mammal - the huge otter (Pteronura brasiliensis) lived: its length was up to 2 m and more including tail. At approach of ecological cataclysms and extinction of a plenty of water animals this species had become extinct. Besides its number was undermined by unlimited hunting of people. Standing empty ecological niche was occupied with uniquitous rodents, and the ancestral species with all inclinations for this changing was the contemporary of otters. The otterodent is the rodent, the descendant of small South-American aquatic rats Ichthyomys. This animal had considerably increased in size in comparison with ancestors: the otterodent is up to 1,5 m in length. Hairless tail (it makes 1/3 length of a body) is flat and serves for swimming - the animal moves, bending backbone in vertical plane. Hinder legs are oar-like, with long fingers and advanced swimming membranes; forepaws have well advanced fingers, with their help the animal holds large catch. wool is dark brown, water-proof, greased with fat from special glands in axillary area. At an adult animal a chest and throat are white. Head is flat, front department of skull and jaws are short, jaw muscles are very strong. Incisors have lemon-yellow coloring of enamel. Bottom incisors are very long, jaws are capable to be opened very widely. It is connected to a way of killing of large catch: the otterodent sticks bottom incisors in a backbone of prey, and then puts bite by top incisors, gnawing through the backbone of catch. Otterodent feeds by fishes and water animals catching in thickness of water, pursuing it actively. Molluscs and crustaceans are digging by animal out of sand by sharp-clawed forepaws. This is the solitary animal, only female and her cubs live together any time. Adult animals keep together only during time necessary for pairing, for some hours. This time the male can look after the female, feeding her with fish. Pregnancy lasts about 4 months, there are 3 - 5 cubs in pack. Females with cubs can be met at any time of year, but it is more often at the end of rain season when rivers are especially rich in fishes. Lair is wide hole in river bank, at the female with cubs the hole is deeper, than at the male, but the entrance is smaller, that preserves cubs against the males inclined to cannibalism.