Slowing metabolism while resting “is tremendously efficient,” says Hugh Tyndale-Biscoe, a comparative physiologist with the Commonwealth Scientific and Industrial Research Organization in Canberra. “When conditions are bad, you just shut your metabolism down and you don’t have to eat so much, but when conditions are good, you can wind it up to six times the rate. There’s no placental mammal that can do that.”
MARSUPIALS The kangaroo, quoll, wombat, and cuscus are marsupials that inhabit ecological niches in Australia equivalent to those of the deer, rat, marmot, and flying squirrel of North America. Nursing young in a pouch reduces the need for extensive maternal investment—a good strategy in an uncertain environment. One disadvantage: Marsupials grow more slowly and thus have smaller brains than placental mammals. Marsupials do not show the spectacular diversity of placental mammals. Australia has around 140 species of marsupials, many extinct or endangered. The only placental mammals native to Australia are rats and bats. South America has three types of marsupials, including 72 species of opossum. North America has only one marsupial species: the Virginia opossum. |
