Mammalia

Mammalia

Mammalia (Mammalia) is a class of vertebrate animals characterized by the presence of mammary glands, which in females produce milk for feeding pups (or offspring), hair or hair, with the exception of dolphins and Of some whales, which only in the embryonic phase have hairs. They are endothermic (with the exception of mole-peeled mice), that is, of constant temperature, also known as "warm-blooded animals".

The brain controls body temperature and the circulatory system, including the heart (with four chambers). Mammals include 5 416 species (including humans), distributed in approximately 1,200 genera, 152 families and up to 46 orders, according to the compendium published by Wilson and Reeder (2005). However new species are discovered every year, increasing that number; And by the end of 2007, the number reached 5 558 species of mammals.

It is believed that the first mammals arose in the Jurassic period, between 176 and 161 million years ago, during the reign of the Dinosaurs. New scientific evidence, however, suggests that mammalian precursors may have arisen at least 208 million years ago during the Upper Triassic period.