Why is an possum a mammal

In the beginning there was the possum

The cradle of the marsupials is in North America. It was here and not in Australia that they first appeared over 100 million years ago. These primeval captors belonged to the opossum family, whose most important representatives today are the possums in North America. While many fossil finds are documented from North America, none have been found in Africa or Asia. From America, the marsupials migrated to the Australian continent via a land connection that still existed at the time and were the first mammals to colonize Australia.

Triumphant advance of the mammals

At the beginning of the Tertiary the Australian continent was isolated from the rest of the land masses, so that from this point on no more mammals could immigrate. At the same time, the dinosaurs, the prevailing group of animals and the greatest competition of the mammals of that time, began to die out worldwide and the now unrivaled mammals began their triumphal march across all continents.

Opossum © Sean F. Werle, Possum Page

In America and Europe, where marsupials are also said to have occurred, it soon turned out, however, that they were not up to the competition of the higher mammals. On the one hand, the higher mammals were characterized by a more advanced reproductive strategy, on the other hand, the marsupials were fatally due to their relatively low intelligence. Compared to their body size, their brains are much smaller than that of the higher mammals. This of course has some disadvantages, for example dogs are more successful than marsupials in acquiring prey due to their more complex hunting structure. Also in the marsupials there are no known social structures as we know them from other mammals. So it came about that today, outside of Australia, there are only marsupials on the American continent.

Isolated Australia

In Australia, however, the situation was completely different. Here the marsupials were the first mammals, and before other mammals could follow and develop freely, the land connection to Australia was severed. At the time of James Cook's (1770-1779) voyages of discovery, apart from the dingo, which was brought to Australia by the indigenous peoples, a few smaller rodents that were probably stranded with driftwood islands in Australia, and some representatives of the bats, there were no higher mammals in Australia. This allowed the marsupials to develop undisturbed to their present diversity.

Such a process, known as adaptive radiation, always occurs when founding individuals conquer a relatively unpopulated living space and find many ecological niches that are still unoccupied. Since this process can take place within a relatively short period of time, more than 175 different species of marsupials have emerged here since Australia was separated from the rest of the land.

Status: 10/6/2006

October 6, 2006