Humans are mammals  Humans are members of a large group of
animals known as mammals (Class Mammalia).  Australian Fur Seal
colony  Australian Fur Seal colony A. McGregor/Nature Focus
© Australian Museum  Mammal diversity  The first mammals evolved
about 190 million years ago. These early mammals were small,
insect-eating creatures that lived at the same time as the
dinosaurs. When the dinosaurs disappeared about 65 million years
ago, mammals began to diversify into many forms. There are now
about 4500 different species of mammals living in almost every
environment on earth including the oceans, fresh water, on and
below the ground, in the treetops and even in the sky.  Mammal
features  All mammals (including humans) have the same
distinctive features. These include:    • fur or hair growing
from the skin   • mammary glands that, in females, produce milk
for feeding the young   • three bones (the malleus, incus and
stapes) in the middle ear for transmitting sound to the inner
ear   • a single bone (the dentary