Mammals

Mammal, common name applied to any warm-blooded animal belonging to the class that includes humans and all other animals that nourish their young with milk, that are covered with varying amounts of hair, and that possess a muscular diaphragm. Mammals have the most highly developed nervous systems of all animals. Most members of the group have four appendages, usually legs. These may be adapted for use as swimming appendages, as in seals, or as wings, …

…One order was made up of small, rodent tike mammals, having gnawing front teeth and grinding teeth with several cusps. A second order consisted of small, carnivorous mammals, having molar teeth equipped with three simple, cone like cusps, that became extinct before the end of the Eocene epoch. A third group of small insectivorous mammals are the probable ancestors of present-day mammals. Of the mammalian subclasses that still exist, themonotremes are unrepresented by fossil remains.