At the beginning of the Tertiary period, about 66.4 million years ago, the world's supercontinent began to break up and the continents began to drift creating areas of isolation for the world's plants and animals. Present-day mammals may be divided into three main groups. These are the monotremes, the placentals, and the marsupials. The mammals that were isolated on the Australian continent were almost entirely marsupials and monotremes. Isolated on this island continent, marsupials radiated to take advantage of the opportunities of their environment, as placental mammals were doing elsewhere in the world. The diversity of Australian marsupials includes kangaroos and wallabies, wombats and koala, marsupial mice and marsupial moles, bandicoots and the Tasmanian wolf -- animals with a wide variety of size and shape, diet, and behavior.
Parallel evolution in different geographic locations has resulted in similar mammalian life forms between placentals and marsupials. This is shown in the chart below:
|BODY TYPE AND LIVING HABITS||PLACENTAL||
|arboreal glider||flying squirrel||
|fossorial herbivore||ground hog||
|digging ant feeder||Myrmecophaga||
(Information credit to Vertebrate Life by F. H. Pough and to the 3/4/91 and 4/1/91 lectures of C. Janis, Brown University.)
Last modified: 23 April 2004