All mammals are endothermic (warm-blooded), have some fur
or hair on their body, and feed their young milk. They have a bony skeleton
with a backbone, and their lower jaw, made of one bone, hinges directly onto
the skull. Mammals breathe using lungs. A few mammals lay eggs, and some carry
their young in pouches, but most have a placenta and give birth to live young.
Mammals are found all over the world, on land, in the air, and in water.
There are about 4,500 species of mammal in a total of 21 orders, of
which the following are a selection.
(duck-billed
platypus, echidna)
Features: lay eggs, short legs, small
head, tiny eyes
(pouched
mammals)
Features: young born at early stage and
cared for in pouch
(odd-toed, hoofed
mammals)
Features: leg’s weight on central
toe
(flesh-eating
mammals)
Features: carnassial (sharp, cheek)
teeth for cutting flesh
(whales, dolphins,
porpoises)
Features: move tail up and down to
swim
(lemurs, apes, monkeys,
humans)
Features: large brain, forward-facing
eyes
(rodents)
Features: incisor teeth grow
continuously, most have good sense of smell and hearing
The duck-billed platypus closes its eyes, ears, and nose when diving
and finds its way using sense receptors around its bill. The platypus lays
eggs. It does not have nipples, so when the young hatch, they suck milk from
the fur around the openings of the milk glands. It lives by rivers in Australia
and Tasmania.
Dolphins, like whales, spend their entire life in the water, but
must still surface to breathe air through their lungs. Their fat reserves,
called blubber, keep them warm in cold seas.
