Australian Placental Animals Native & Introduced Placental Mammals in Australia

Photo: Dingoes Australian placental mammals

Placental mammals develop their offspring inside their body in a uterus to which is attached an organ called a placenta (hence the name placental). They give birth to babies that are far more advanced in their development than marsupial and monotreme mammals.

Because of Australia's isolation, there are few native placental mammals. The first of these to arrive in Australia were bats and rodents that flew or floated across the oceans to Australia from neighbouring islands between 5-15 million years ago. Marine mammals such as the Dugong and Australian seal also swam their way to Australia sometime in the very distant past. The next to arrive were the Aborigines who came to Australia around 50,000 years ago (yes humans are placental mammals too). Ancient seafarers from Asia introduced the dingo about 5,000 years ago. It was only with the arrival of European settlers in 1778 that a substantial number of other placental mammals such as cattle and sheep were introduced to Australia.

• Characteristics of Placental Mammals


 

 

Goat

Goats escaped into the wild and now cause significant damage to the environment by overgrazing and depriving other animals of food.

 

Rakali (Water Rat)

The Rakali is a semi-aquatic native placental mammal. It lives in burrows on the banks of rivers. It eats insects, fish, crustaceans, snails, and frogs.

 

Rat

Black and brown rats arrived on board the first European ships to come Australia . They carry diseases and eat farm crops.

 

Pig (Feral)

Feral Pigs are the descendants of pigs brought to Australia by European settlers. Many were allowed to roam and soon became wild.

 

Sea Lion

Australian sea lions stocky bodies, a large head, and short narrow flippers. The male is twice as large as the female. They hunt fish and squid.

 

Whale

Humpback whales travel up from the Antarctic to give birth and feed their young. They can grow to 12 – 16 metres and weight 36,000 kgs.

 

Benteng

The Banteng was introduced by the British army in 1849 at a remote outpost in Northern Australia which was later abandoned.

 

Dolphin

Dolphins are very vocal, playful, intelligent, social animals that live in groups of up to 15 animals. They feed on invertebrates, fish, and squid.

 

Farm Animals

Introduced farm animals such as sheep and cattle are vital to the Australian livestock industry. They contribute significantly to the economy.

 

Characteristics of Placental Mammals What Makes Placental Mammals Different

rakali rat

Photo: Rakali Water Rat - Native Placental Mammal

Photo: Diagram of human placenta

Birth

The key characteristic of a placental mammal is that it gives birth to babies that are far more advanced in their development than monotremes and marsupials. They do this by developing their offspring inside their bodies 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.

Photo: Cow - An introduced placental mammal

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.

• Differences Between Placental, Marsupial and Monotreme Mammals