In some species, however, this pouch may be poorly formed or even absent. Common marsupials include the kangaroos and koalas of Australia and New Guinea, the Tasmanian devil of Tasmania, and the opossums of North and South America. Modern marsupials do not grow as large as some placental mammals, though fossils indicate that some ancient Australian marsupials were as large as elephants. The largest living marsupials are the red and gray kangaroos of Australia. Females, however, are smaller.
Most marsupials range in size between a small cat and an average-sized dog.
All have hair, and all nurse their young with milk from the mother's mammary, or milk-producing, glands. Despite such similarities, however, certain aspects of marsupial skeletal structure are distinctly different from other mammals. For example, the skull and brain are smaller than those of comparably sized placental mammals. In addition, most marsupial species have 40 to 50 teeth, more than most placental mammals. Marsupials possess a pair of small bones in the pelvic region, called epipubic bones, that may have served to help support the reproductive pouch in ancestral marsupial forms.