Australian Placental Mammals Placental Mammals in Australia
Placental Animals What is a Placental Animal?
Placental mammals constitute over 5,000 difference species of mammals in the world. These include animals such as humans, aardvarks, cats and horses. 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 was the bat which flew to Australia from the neighbouring islands. The next were humans, known as the Aboriginals, 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 by these immigrants.
Placental (pla-cen-tal) pronunciation.
Characteristics of Placental Mammals
Placental mammals constitute over 5000 difference species of mammals and include animals as varied as humans, aardvarks, cats, horses and even whales.
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.
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.
In general placental mammals have a body temperature of 38°C. This is about 3°C higher than most marsupial.
The basal metabolic rates (BMRs) of placental mammals is about 30% higher than marsupials.
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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