The word mammal is derived from the milk-producing mammary
glands that are unique to the class Mammalia. Mammals, including
humans, are generally regarded as the most evolved or advanced
of the vertebrates (animals with a backbone and spinal cord).
Some of the typical diagnostic features of mammals may be shared
with other vertebrates or be absent in some groups, as defined
in the following list of characteristics:  1) mammary glands
which produce milk for nourishing the young;  2) all give birth
to living young, except the order Monotremata (eg, duck-billed
platypus), which is egg laying;  3) endothermic (warm blooded,
shared with birds) - the ability to maintain a constant body
temperature;  4) a body covering of hair (unique to mammals, but
reduced in some forms) or a subcutaneous layer of blubber (in
whales where hair is extremely reduced or absent in adults);  5)
sweat glands in the skin aid in heat loss;  6) lower jaws of
only one bone on each side which articulates directly with the
cranium;  7) 3 pai