What is a mammal?

Mammals are vertebrates, which means that they have a backbone. They have hair/fur someone on their body and feed their young milk. They produce the milk from glands called mammary glands which are modified sweat glands. The name ‘mammals’ comes from these glands.

Mammals are endothermic which means that they are warm-blooded and able to maintain their own body temperature. Their body temperature remains the same all the time even though the temperature of their environment might change.

They produce the milk from glands called mammary glands which are modified sweat glands. The name ‘mammals’ comes from these glands.


Types of Mammals

Mammals belong to the class mammalia. Within this class there are three subclasses monotremes, marsupials and placental mammals. Details of what makes each group different are below.


There are only three species of mammals that are monotremes, the platypus and two species of echidnas.

These types of mammals produce milk and have hair but they lay eggs. Their eggs are similar to reptile eggs which are leathery and they hatch young who are not well developed. They produce milk for the young which comes from pores in the skin not from a nipple. They young are carried by clinging to the fur on their mothers stomach.

Learn more about monotremes with our focus fact file.

The echidna is a Monotreme


Marsupials are animals in which the female of the species has a pouch. Young are born undeveloped and upon birth climb down the mother's stomach and in to the pouch.

They will latch onto a nipple inside the pouch and nurse just about constantly until they have grown enough to survive outside of the pouch.

Learn more about marsupials with our focus fact file

Kangaroo Island Kangaroo 3

Placental Mammal

This group accounts for most of the mammals and their young develop inside the mother while being attached to a placenta. Due to the placenta they are able to get the oxygen and nutrients that they need to develop to an advanced stage before they are born.

Humans are an example of placental mammals. Other examples are household pets such as dogs and cats, farm animals such as cows, horses, sheep and wild animals such as lions, bears, rodents and bats.

Learn more about placental mammals with our focus fact file

black and white ruffed lemur

A study from 2018 published in the journal of mammalogy suggests there are currently around 6,500 species of mammals on Earth.


Mammal Fact Files