List the specific characteristics of mammals.

Mammals have a number of specific traits that distinguish them from all other animals. First of all, this concerns the fact that the overwhelming majority of mammals are viviparous and do not lay eggs or eggs. Also, if in other animals the young are fed either immediately with adult food or with a semi-digested version of it, then mammals have mammary glands and feed the young with milk. Even in mammals, the limbs are usually located perpendicular to the spine.