THE MARSUPIALS
The word marsupial means "pouched," and refers to the most characteristic peculiarity of the nonplacental division (order Marsupialia), which is the possession of a more or less pocketlike fold in the skin of the abdomen of the females within which the extremely immature young are nourished.
The egg-laying mammals, also nonplacental, have the young inclosed in a protective shell that they keep warm, as do the birds, until the embryo is sufficiently matured to be safely born. In the marsupials nature meets the difficulty another way. The embryo is but little advanced when born, in fact it is utterly helpless and minute, being, even in the case of the largest kangaroos, hardly as big as a mouse. It would be fatal, of course, to turn it loose upon the world; and therefore the mother is provided with the pouch already described.
The instant an embryo is born the mother picks it up and places it within the pouch, where it crawls about until it touches and instinctively takes hold of one of the threadlike teats. As it gets stronger it leaves the pouch now and then, but returns to it for nursing, sleeping, and protection when alarmed, until finally it departs altogether.
This description applies to the most advanced families of the order. In the oldest and most generalized families of marsupials, such as the banded anteaters, there is virtually no pouch at all.
As almost the whole marsupial tribe are natives of Australasia, it is odd that the family with which we must begin a list of them—the true opossums—should be American, and quite unknown in Australia. This is explainable when it is known that this family (Didelphidæ) is the most archaic of this ancient tribe, and was well established in Cretaceous times, and then and later was widely distributed in Europe and on this continent; yet so little change has occurred in the race that teeth from the Laramie formations of Wyoming are hardly distinguishable from those in the jaws of our 'possum-up-a-gum-tree to-day. No wonder the quaint creature is hoary and wrinkled; he is a very Methuselah among mammals, and looks it! All opossums seem to have disappeared from Europe before the close of the Miocene, but continued to survive numerously in South America. They probably owe their long career, in competition with animals of so much higher grade, to their small size, forest life, nocturnal habits, ability to eat all sorts of food, and, most of all, to their great fecundity. Our common opossum is the most northern of its kind, and ranges over the whole country as far north as the latitude of Lake Erie; it appears never to have crossed the Hudson River until comparatively recent times, but is now frequently met with in New England and on Long Island. It is at home in all sorts of places, except, perhaps, on the dry plains, for it is primarily an arboreal animal, aided in climbing about trees by its naked, prehensile tail, by which it may hang to a branch while using its forefeet to rob a bird's nest or gather fruit. It will eat anything it can get hold of, and with its sharp teeth, which number fifty, will kill animals as large as itself; hence it is a destructive raider of henroosts and sitting birds as well as a seeker of mouse nests and insects.
Opossums are amazingly prolific, and have broods of a dozen or more in many cases. These often crawl on the mother's back, and cling with claws and twisted tails to her fur and tail, and so are carried about. Burdened by these kittens she hunts daily—or rather at night, for the most part—and defends them savagely and bravely against foxes and other enemies, often successfully standing off the farmer's dogs. With a family to defend, or when faced by any foe that is at all equal to its powers, the opossum does not resort to "playing 'possum," for this is a last resource when surprised and "cornered" by an overwhelming danger that it can neither avoid nor cope with.
The proverbial feigning of death by this animal (many other small animals do the same) has excited much popular interest, and has received many explanations. I have suggested that it is a survival of a practice which in past ages had been an advantageous ruse of the ancestors of the opossums.
Several other species of opossums exist in Central and South America, some much smaller than ours and one hardly bigger than a mouse. One kind, the "yapock," is aquatic, dwelling on land only during the infancy of its progeny, and until they are old enough to be taught to swim. All the marsupials inhabiting the Americas (except a rare little molelike one in Patagonia), belong in the family Didelphidæ; but this family is not known in Australia, where the so-called "opossums" belong to a different tribe. They were named after our common northern opossum, which was known to science before Australia and its pouched fauna were discovered.
One of the extraordinary things in zoölogy is that Australia, and the near-by islands that constitute with it a faunistic province, has no indigenous mammals (except a few mice and bats) other than marsupials, which have become so diversified as to represent the varied kinds of animals seen elsewhere; and no marsupials live anywhere else in the world except our single and primitive American family. This curious situation has caused much discussion. It is known that in late Mesozoic times marsupials were scattered all over the globe, but became exterminated everywhere outside of Australasia and America long before the present era. The Australian marsupials are supposed to be the survivors, flourishing in a favorable region; but why no other mammals survived there is still a puzzle. Another theory is that Australia, regarded as formerly a part of a much larger southern continent, is the original center from which the ancestors of the Marsupialia spread, but failed to maintain their race outside of their original home, with which South America was then connected.
The most archaic of these marsupials is the celebrated Tasmanian "wolf," or thylacine, which resembles in size and shape a pointer dog, but with a longer muzzle, and that long tail which seems to be a general characteristic of the Marsupialia. It is brownish gray, with a row of darker bands crossing the hinder half of the back, and is one of the most swift-footed and savage hunters in the world. It is confined to Tasmania, where it became so destructive to sheep when the island was settled that it was killed off until almost exterminated. This island was the home, also, of another smaller beast, looking somewhat like a wolverine with the head of a hyena, which was so morose, savage, and untamable that the settlers named it "Tasmanian devil," and destroyed it as rapidly as they could. It hid by day in some rock den and made its forays at night. This truly diabolic creature belonged to the family of dasyures, which is represented in Australia by several small, predatory beasts called "native cats." They fill the rôle there of our northern martens and weasels, and most of their time is passed in trees, although some are fond of hunting amid rocks and brush. They like to come about ranches and villages, where they are the pest of poultry keepers, but are rarely domesticated, even partly. Another carnivorous group (phascogales) contains the "pouched mice," which are not mouselike, except in size, but have more the nature of shrews that live in trees and hunt birds and any small creatures they can catch.
Of the phalangers a curious specimen is the wombat, named "native bear" by the early colonists—an animal about the size of our woodchuck, shaped like a miniature bear, and living mainly on roots, which it digs at night with its powerful claws; its thick fur makes its skin valuable in market. Related to it structurally, but much like our gray squirrel in shape, and having an even longer and more bushy tail, is the charming sugar squirrel, which dwells in trees, and sails in long flights from tree to tree in the twilights and on moonlight nights just as do our flying squirrels; there are also tree phalangers so small they are called "flying mice." Other tree-living phalangers are the "opossums" of Australia, whose soft gray pelts are exported in great numbers to foreign fur markets.
| A KANGAROO MOTHER |
| Showing young carried in the abdominal pouch |
The kangaroos and wallabies (Macropodidæ) represent the highest development of the marsupial type, and number some fifty species spread over all Australia and New Guinea. While the majority inhabit open grassy plains, others brushy districts and rocks, and a few dwell in trees, the kangaroos proper include half a dozen of the largest kinds, the commonest of which is the great gray "boomer" or "forester," of the colonists, often seen in menageries. It stands four to five feet tall, with a tail thirty to thirty-six inches long; but this size is considerably exceeded by that of the red or woolly kangaroo, of eastern and southern Australia. Furthermore, fossil remains show that in the Pleistocene era kangaroos far bigger than even these existed there in numerous extinct species—one, for instance, whose skull alone measured nearly a yard in length. These animals take the place in Australia of the deer of northern countries. They are very gregarious, and are always to be met with in droves. Each drove frequents a certain district and has its particular camping and feeding grounds. The animal has a dreadful weapon of defense in the powerful hind claw, which it can use like the tusk of a boar.
The smaller kangaroos are called "wallabies," or brush kangaroos, and frequent scrub jungle and rocky places. These furnish most of the skins and leather sent to European markets and, like the big species of the plains, have been greatly reduced in numbers by hunters and sheep herders. Some of them are confined to the rough deserts and mountains, where they jump about the rocks with astonishing agility. One small genus includes the swift harelike species that resemble our jack rabbits in habits; and there are also the "dorca" kangaroos, which are arboreal in habit and handsomely colored. Another group are ratlike in form, colors, and manners, running rather than leaping, and dwelling among scrub and grass, scratching the ground all day in search of the roots upon which they feed, and making havoc in the frontiersman's potato patches. Several kinds have prehensile tails, which they use apparently only to carry to their underground homes the long grass of which they make their beds. They associate in connected burrows like a rabbit warren.
In the varied forms and functions they present, as beasts of prey, as grazers or root diggers, as ground-running, tree-climbing, burrowing or cave-haunting forms, some solitary and slow, others agile and gregarious, the marsupial tribe in its isolated corner of the earth exhibits an epitome of the whole mammalian world. It shows in a conspicuous way how the necessity and habit of making a living in varied circumstances, and exposed to lively competition, restricting every species to a particular manner, brings about a suitable modification of structure.