Australian Placental Mammals Native & Introduced Placental Mammals in Australia


Placental Animals What is a Placental Animal?

Mammals are divided into three groups based on how their babies develop. These are placental, marsupial and monotreme mammals. The key characteristic of a placental mammal is that gives birth to babies that are far more advanced in their development than monotremes and marsupials. They do this by developing the baby inside their body in a uterus.


Placental Animals in Australia When did Placental Mammals Arrive in Australia?

Placental mammals constitute over 5,000 difference species of mammals in the world. But because of Australia’s long isolation from the rest of the world non of these lived in Australia until relative recent times. The first to arrive on the mainland of Australia were bats and rodents that flew or floated across to Australia from the neighbouring islands. Marine mammals such as the Dugong and Australian seal also swam their way to Australia sometime in the distant past. The next group to arrive were humans, known as the Aborigines, who arrived in Australia around 50,000 years ago. Ancient seafarers from Asia introduced the dingo about 5,000 years ago. It was only with the arrival of European settlers in 1778 that large varieties of placental mammals such as cattle and sheep were introduced to Australia.



Characteristics of Placental Mammals What Makes Placental Mammals Different

The key difference between placental mammals and other sorts of mammals such as monotremes and marsupials is the way in which they develop their embryos.

Birth

The key characteristic of a placental mammal is that gives birth to babies that are far more advanced in their development than monotremes and marsupials. They do this by developing the baby inside their body in a uterus. The baby is attached to the uterus by an organ called a placenta which in turn is connected to the mother's blood supply. In this way the baby gets all the nutrients it needs to grow. The term "placental" is somewhat misleading because marsupial mammals also have a rudimentary placenta. The key difference is that in a placental mammal the baby remains attached to the placenta inside the mother's uterus for a relatively longer period of time compared to a marsupial. Placental mammals are sometimes called eutherian mammals to try to clear up this confusion. Because they have a uterus, placental mammals do not have a pouch.

Lactation

Placental mammals provide nourishment for their young by providing them with milk through a teat or nipple. Because the baby is already relatively well developed before it is born the period of lactation is much shorter than for equivalent marsupials.

Body Temperature

In general placental mammals have a body temperature of 38°C. This is about 3°C higher than most marsupial.

Metabolism

The basal metabolic rates (BMRs) of placental mammals is about 30% higher than marsupials.

Other

In general placental mammals have less teeth than marsupials. They also grow two pairs of teeth, namely milk teeth and adult teeth.

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