Mammals are vertebrates with hair, mammary glands used to suckle young with milk, a diaphragm, three bones in the middle ear, and a lower jaw made up of a single pair of bones that articulates in a unique way with the skull.
Mammals are divided into three groups - monotremes, marsupials and placentals, all of which have fur, produce milk and are warm-blooded.
Monotremes are the platypus and echidnas and the females lay soft-shelled eggs.
Marsupials give birth to small, poorly developed young and most female marsupials, such as kangaroos, wallabies and the Koala, have pouches.
Placental mammals, like humans, whales, rodents and bats, differ from monotremes and marsupials in that they generally give birth to well-developed young.
Mammals are a diverse group, but all mammals-
- produce milk to feed their young
- have hair or fur
- have a unique jaw structure
- are warm-blooded
Evidence that mammals evolved from reptiles is provided by fossils 250-180 million years old. These fossils include a large number of species that share so many reptilian and mammalian features that they cannot be assigned to either group.
There are 17 orders of terrestrial (land) mammals in Australia.; made up of 4 groups- monotremes, marsupials, rodents and bat. This includes endemic species native to Australia.
All 3 groups of marine mammals, cetaceans, seals and dugongs occur in Australian coastal waters.