In tropical forests of Neocene epoch rodents represent one of the most typical groups of mammals. These animals have great range of habitats – from underbrush up to forest canopy – and occupy various ecological niches. Due to ecological plasticity rodents had successfully gone through the time of anthropogenous pressure and had reached blossoming in Neocene epoch. Their adaptations for survival are very diverse, and some Neocene species have developed adaptations unknown in human epoch. The massive sluggish rodents similar a little to badgers with long hairless nonflexible tails live in forests of Southeast Asia. They are large descendants of any from numerous species of rats (Rattus); the body length of adult individual reaches 50 – 60 cm (and tail is about 40 cm long), and weight is up to 7 – 8 kg. They live in family couples and constantly search for food together. The body of these rodents is covered with rigid wool of rusty-brown color, lighter on stomach. Head is colored very brightly and sharply contrasts with body colouring: on white background longitudinal black strips stretch – some narrow strips on forehead and one wide stroke on each cheek. Such colouring is very well perceived by predators lack of color vision, and is remembered by them for a long time after acquaintance to protective adaptations of these rodents. The bite of these rodents is poisonous. Poisonous mammals are known in human epoch – they are monotremes and some insectivores. They secreted their own poison from special glands: duck-bill from spurs on legs, and shrews from modified salivary glands. Poisonous shrew lives in Neocene in forests of Europe. Poison-toothed giant rat differs from them in origin of poison: in modified salivary glands of this rodent the poisons received from plants are accumulated. At an attack of predator poison-toothed giant rat first of all displays to the enemy readiness to protect itself, widely opening mouth and bristling wool on head. If the enemy continues attempts of attack, the rodent counterattacks it and bites strongly. On top incisors of poison-toothed giant rat from external edge there is a groove which gradually goes deeper when animal is older and turns to closed channel. The duct of specialized salivary gland opens in it. Obviously, at ancestors of these rats salivary glands began initially to filter and to excrete a part of alcaloids received with food, which has allowed rodents to eat poisonous plants, avoiding a competition to other herbivores. Then additional function gradually turned to basic one, and salivary glands had turned to stores of poison. The diet of these rodents includes a significant part of poisonous plants of various families, usually spurges and sumach. When poison-toothed giant rat chews poisonous plants, poison from their sap is intensively absorbing by mucous membranes of mouth and is immediately filtered in salivary glands. This species has very expressed immunity to plant poisons, and also to poisons of snakes and numerous invertebrates. Due to such diet poison-toothed giant rat avoids food competition to other species of animals. Voice of this rodent represents silent sounds similar to pig grunting and puffing. Alarm call of poison-toothed giant rats is shrill whistle heard from very long distance. Using it, these rodents warn each other of occurrence of predator. Protecting itself from the enemy, poison-toothed giant rat displays to it contrast colouring of head and utters loud squeal. If the predator does not stop an attack, poison-toothed giant rat puts to it deep snaps and injects poison in wounds at these moments. These animals live in pairs in large holes arranged under roots of big trees. The pair at poison-toothed giant rats is kept during very long time – partners may raise posterity in common within several years in succession. Within one year this rat gives birth to two litters numbering 2 – 4 cubs. They are born blind, but covered with rare wool. Female looks after them within one month while cubs will develop enough to search for food independently and to follow parents. The first months of life poison-toothed giant rat lacks characteristic poisonous bite, because it has weak immunity to poisons, and eats nonpoisonous parts of plants. At this time only protection of this animal is its own care. Young animal gradually includes poisonous plants in diet, and later becomes capable to accumulate poison in salivary glands.