Marsupials adapted to a variety of environments

Palorchestes, an extict marsupial

    The extinct giant marsupials are just one example of many animals that began their evolution as well-adapted organisms but became nonadapted in altered circumstances and so died out. Other marsupials of Australasia, however, were more successful than their giant relatives and have survived to modern times. They exploited the opportunities at hand and so spread out into a variety of habitats. The force in evolution whereby evolving animals enter new environments and become quite different from one another is called adaptive radiation. Some marsupials became predators and developed teeth for their flesh-eating habits; others took to the trees and developed organs for climbing; still others became burrowing animals. The marsu­pials of a particular way of life came to resemble the placentals of other lands who had the same kind of habits. This phenomenon in evolution, in which basically different animals with similar habits take on similar characteristics, is termed convergence.

    In modern times the marsupials of Aus­tralasia have seriously decreased in numbers; some species have become extinct. The primary causes seem to be man and his introduced animals. The marsupials have been hunted by man for food and fur and wantonly killed for "sport." Man's agricultural and stock-raising activities have drastically taken away good grazing land from the herbivorous kangaroos and wallabies. The introduced animals, especially the dingo, the fox and the domestic cat, have destroyed thousands of marsupi­als. Since they reproduce slowly, usually having but one or two young a year, they cannot quickly replace their lost numbers. During a period of drought, many herbiv­orous marsupials and the introduced rabbits will starve. When favorable conditions return, the prolific rabbits soon reestablish themselves and consume much vegetation, whereas the marsupial population seldom recovers itself completely and must constantly compete against the voracious rabbit population for food.