Popular Science Monthly/Volume 8/February 1876/Natural History of the Kangaroo
By ST. GEORGE MIVART, F. R. S.
THE kangaroos have now become familiar objects to all who visit our Zoölogical Gardens, or who are familiar with any considerable zoölogical museum.
Their general external form, when seen in the attitude they habitually assume when grazing (with their front limbs touching the ground), may have recalled to mind, more or less, the appearance presented by-some hornless deer. Their chief mode of locomotion (that jumping action necessitated by the great length of the hind-limbs) must be familiar to all who have observed them living, and also, very probably, the singular mode in which the young are carried in a pouch of skin in the front of the belly of the mother.
But "What is a kangaroo?" The question will raise in the minds of those who are not naturalists the image of some familiar circumstances
Fig. 1.—Kangaroo (Macropus).
like those just referred to. But such image will afford no real answer to the question. To arrive at such an answer it is necessary to estimate correctly in what relation the kangaroo stands to other animals—its place in the scale of animated beings—as also its relations to space and time; that is, its distribution over the earth's surface to-day, in connection with that of other animals more or less like it, and its relation to the past life of this planet, in connection with similar relations of animals also more or less like it. In other words, to understand what a kangaroo is, we must understand its zoölogical, geographical, and geological conditions. And my task in this paper is to make these conditions as clear as I can, and so to enable the reader to really answer the question, "What is a kangaroo?"
But before proceeding to these matters, let us look at our kangaroo a little closer, and learn something of its structure, habits, and history, so as to have some clear conceptions of the kangaroo considered by itself, before considering its relations with the universe (animate and inanimate) about it.
The kangaroo (Fig. 1) is a quadruped, with very long hind-limbs and a long and rather thick tail. Its head possesses rather a long muzzle, somewhat like that of a deer, with a pair of rather long ears. Each fore-paw has five toes, urnished with claws. Each hind-limb has but two large and conspicuous toes, the inner one of which is much the larger, and bears a very long and strong claw (Fig. 2). On the inner
Fig. 2.—Foot of Kangaroo.
side of this is what appears to be a very minute toe, furnished with two small claws. An examination of the bones of the foot shows us, however, that it really consists of two very slender toes united together in a common fold of skin. These toes answer to the second and third toes of our own foot, and there is no representative of our great-toe—not even that part of it which is inclosed in the substance of our foot, called the inner metatarsal bone. Two other points are specially noteworthy in the skeleton. The first of these is that the pelvis (or bony girdle to which the hind-limbs are articulated, and by which they are connected with the back-bone) has two elongated bones extending upward from its superior margin in front (Fig. 4, a). These are called marsupial bones, and lie within the flesh of the front of the animal's belly. The other point is that the lower, hinder portion of each side of the lower jaw (which portion is technically called the "angle") is bent inward, or "inflected," and not continued directly backward in the same plane as the rest of the lower jaw.
A certain muscle, called the cremaster muscle, is attached to each marsupial bone, and thence stretches itself over the inner or deep surface of the adjacent mammary gland or "breast," which is situated low down, and not in the breast at all.
The kangaroo's teeth consist of three on each side in the front of the mouth, and one on each side below. These eight teeth are what are called incisors. At the back of the mouth there are live grinding-teeth on each side above and five below, and between the upper grinders and incisors another pointed tooth, called a canine, may or may not be interposed. Such a set of teeth is indicated by the following formula, where I stands for incisors, C for canines, and M for grinding-teeth or "molars." The number above each line indicates the teeth of each denomination which exist on one side of the upper jaw, and the lower number those of the lower jaw:
The total number of incisor teeth of both sides of each jaw may therefore be expressed thus: I 6⁄2.
Such is the general structure of an adult kangaroo. At birth it is strangely different from what it ultimately becomes.
It is customary to speak of the human infant as exceptionally helpless at birth and after it, but it is at once capable of vigorous sucking, and very early learns to seek the nipple. The great kangaroo, standing some six feet high, is at birth scarcely more than an inch long, with delicate naked skin, and looking like part of an earthworm. But, in such feeble and imperfectly developed condition, the young-kangaroo cannot actively suck. The mother therefore places it upon one of her long and slender nipples (the end of which is somewhat swollen), this nipple entering its mouth, and the little creature remaining attached to it. The mother then, by means of the cremaster muscle (before spoken of), squeezes her own milk gland, and so injects milk into the young, which would thus be infallibly choked but for a noticeable peculiarity of its structure, admirably adapted to the circumstances of the case.
In almost all beasts, and in man also, the air-passage or windpipe (which admits air to and from the lungs) opens into the floor of the mouth, behind the tongue and in front of the opening of the gullet. Each particle of food, then, as it passes to the gullet, passes over the entrance to the windpipe, but is prevented from falling into it (and so causing death by choking) by the action of a small cartilaginous shield (the epiglottis). This shield, which ordinarily stands up in front of the opening into the windpipe, bends back and comes over that opening just when food is passing, and so, at the right moment, almost always prevents food from "going the wrong way." But, in the young kangaroo, the milk being introduced, not by any voluntary act of the young kangaroo itself, but by the injecting action of its mother, it is evident that, did such a state of things obtain in it as has been just described, the result would be speedily fatal. Did no special provision exist, the young one must infallibly be choked by the intrusion of milk into the windpipe. But there is a special provision for the young kangaroo; the upper part of the windpipe (or larynx), instead of lying as in us, and as in most beasts, widely separated from the hinder opening of the nostrils, is much raised (Fig. 3, a). It is in fact so elongated in the young kangaroo that it rises right up into the hinder end of the nasal passage, which embraces it. In this way there is free entrance for air from the nostrils into the windpipe by a
Fig. 3.—1. Dissected Head of Young Kangaroo.—a Elongated Larynx; b, Cavity of Mouth. 2. Nipple of Mother.
passage shut off from the cavity of the mouth. All the time the milk can freely pass to the back of the mouth and gullet along each side of this elongated larynx, and thus breathing and milk-injection can go on simultaneously, without risk or inconvenience.
The kangaroo browses on the herbage and bushes of more or less open country, and, when feeding, commonly applies its front-limbs to the ground. It readily, however, raises itself on its hind-limbs and strong tail (as on a tripod) when any sound, sight, or smell, alarms its natural timidity (Fig. 1).
Mr. Gould tells us that the natives (where it is found) sometimes hunt these animals by forming a great circle around them, gradually converging upon them, and so frightening them by yells that they become an easy prey to their clubs.
As to its civilized hunters, the same author tells us that kangaroos are hunted by dogs which run entirely by sight, and partake of the nature of the greyhound and deerhound, and, from their great strength and fleetness, are so well adapted for the duties to which they are trained, that the escape of the kangaroo, when it occurs, is owing to peculiar and favorable circumstances; as, for example, the oppressive heat of the day, or the nature of the ground; the former incapacitating the dogs for a severe chase, and the hard ridges, which the kangaroo invariably endeavors to gain, giving him great advantage over his pursuers. On such ground the females in particular will frequently outstrip the fleetest greyhound; while, on the contrary, heavy old males, on soft ground, are easily taken. Many of these fine kangaroo-dogs are kept at the stock-stations of the interior, for the sole purpose of running the kangaroo and the emu, the latter being killed solely for the supply of oil which it yields, and the former for mere sport or for food for the dogs. Although I have killed the largest males with a single dog, it is not generally advisable to attempt this, as they possess great power, and frequently rip up the dogs, and sometimes even cut
Fig. 4.—Skeleton of the Kangaroo.—a, Marsupial Bones.
them to the heart with a single stroke of the hind-leg. Three or four dogs are more generally laid on; one of superior fleetness to "pull" the kangaroo, while the others rush in upon it and kill it. It sometimes adopts a singular mode of defending itself, by clasping its short, powerful fore-limbs around its antagonist, then hopping away with it to the nearest water-hole, and there keeping it beneath the water until drowned.
The kangaroo is said to be able to clear even more than fifteen feet at one bound.
Rapidity of locomotion is especially necessary for a large animal inhabiting a country subject to such severe and widely-extending droughts as in Australia. The herbivorous animals which people the plains of Southern Africa—the antelopes—are also capable of very rapid locomotion. In the antelopes, however, as in all hoofed beasts, all the four limbs (front as well as hind) are exclusively used for locomotion. But in kangaroos we have animals requiring to use their front pair of limbs for the purposes of more or less delicate manipulation with respect to the economy of the "pouch." Accordingly, for such creatures to be able to inhabit such a country, the hind pair of limbs must by themselves be fitted alone to answer the purpose of both the front and hind limbs of deer and antelopes. It would seem, then, that the peculiar structure of the kangaroo's limbs is of the greatest utility to it; the front pair serving as prehensile manipulating organs, while the hind pair are, by themselves alone, able to carry the animal great distances with rapidity, and so to traverse wide arid plains in pursuit of rare and distant water. The harmony between structure, habit, and climate, was long ago pointed out by Prof. Owen.
Fig. 5.—Teeth of Kangaroo.
The kangaroo breeds freely in this country, producing one at a birth. We have young ones every year in our Zoölogical Gardens. A large number of them are reared to maturity, and altogether our kangaroos thrive and do well. One born in our gardens was lately in the habit of still entering the pouch of its mother, although itself bearing a very young one within its own pouch. These animals have been already more or less acclimatized in England. I have myself seen them in grounds at Glastonbury Abbey. Some were so kept in the open by Lord Hill, and some by the Duke of Marlborough. A very fine herd is now at liberty in a park near Tours, in France.
It is a little more than one hundred and five years since the kangaroo was first distinctly seen by English observers. At the recommendation and request of the Royal Society, Captain (then Lieutenant) Cook set sail in May, 1768, in the ship Endeavor, on a voyage of exploration, and for the observation of the transit of Venus of the year 1769, which transit the travelers observed, from the Society Islands, on June 3d of that year. In the spring of the following year the ship started from New Zealand to the eastern coast of New Holland, visiting, among other places, a spot which, on account of the number of plants found there by Mr. (afterward Sir Joseph) Banks, received the name of Botany Bay. Afterward, when detained in Endeavor River (about 15° south latitude) by the need of repairing a hole made in the vessel by a rock (part of which, fortunately, itself stuck in the hole it made). Captain Cook tells us that on Friday, June 22, 1770, "some of the people were sent on the other side of the water, to shoot pigeons for the sick, who at their return reported that they had seen an animal, as large as a greyhound, of a slender make, a mouse-color, and extremely swift." On the next day, he tells us: "This day almost everybody had seen the animal which the pigeon-shooters had brought an account of the day before; and one of the seamen, who had been rambling in the woods, told us on his return that he verily believed he had seen the devil. We naturally inquired in what form he had appeared, and his answer was, says John, 'As large as a one-gallon keg, and very like it; he had horns and wings, yet he crept so slowly through the grass that, if I had not been afeared, I might have touched him.' This formidable apparition we afterward, however, discovered to have been a bat (a Flying Fox).... Early the next day," Captain Cook continues, "as I was walking in the morning, at a little distance from the ship, I saw myself one of the animals which had been described; it was of a light mouse-color, and in size and shape very much resembling a greyhound; it had a long tail also, which it carried like a greyhound; and I should have taken it for a wild-dog if, instead of running, it had not leaped like a hare or deer." Mr. Banks also had an imperfect view of this animal, and was of opinion that its species was hitherto unknown. The work exhibits an excellent figure of the animal. Again, on Sunday, July 8th, being still in Endeavor River, Captain Cook tells us that some of the crew "set out, with the first dawn, in search of game, and in a walk of many miles they saw four animals of the same kind, two of which Mr. Banks's greyhound fairly chased; but they threw him out at a great distance, by leaping over the long, thick grass, which prevented his running. This animal was observed not to run upon four legs, but to bound or leap forward upon two, like the jerboa." Finally, on Saturday, July 14th, "Mr. Gore, who went out with his gun, had the good fortune to kill one of these animals which had been so much the subject of our speculation;" adding, "This animal is called by the natives kanguroo. The next day (Sunday, July 15th) our kanguroo was dressed for dinner, and proved most excellent meat."
Such is the earliest notice of this creature's observation by Englishmen; but Cornelius de Bruins, a Dutch traveler, saw, as early as 1711, specimens of a species (now named after him, Macropus Brunii), which he called Filander, and which were kept in captivity in a garden at Batavia. A very fair representation of the animal is given—one showing the aperture of the pouch. This species was, moreover, described both by Pallas and by Schreber.
It is not improbable, however, that kangaroos were seen by the earlier explorers of the western coast of Australia; and it may be that it is one of these animals which was referred to by Dampier, when he tells us that on August 12, 1699, "two or three of my seamen saw creatures not unlike wolves, but so lean that they looked like mere skeletons."
Having now learned something of the structure, habits, and history of the kangaroo, we may proceed to consider its zoölogical, geographical, and geological relations, in order to arrive at the best answer we may to our initial question, "What is a kangaroo?"
First, as to its zoölogical relations: and here it is necessary to recall to mind certain leading facts of zoölogical classification, in order that we may be better able to see with what creatures the kangaroo is, in various degrees, allied.
The whole animal population of the globe is spoken of under the fanciful term, the "animal kingdom," in contrast with the world of plants, or "vegetable kingdom."
The animal kingdom is divided into certain great groups, each of which is called a sub-kingdom; and one, the highest of these subkingdoms (that to which we ourselves belong), bears the name vertebrata, and it includes all beasts, birds, reptiles, and fishes; and the name refers to the series of bone called vertebræ, of which the backbone or spinal column (and all vertebrata have a spinal column) is generally made up.
Each sub-kingdom is made up of subordinate groups, termed classes; and thus the vertebrate sub-kingdom is made up of the class of beasts or Mammalia (so called because they suckle their young), the class of birds, and other classes.
Each class is made up of subordinate groups, termed orders; each order is further subdivided into families; each family is made up of genera; while every genus comprises one, few, or many species.
In considering the zoölogical relations of the kangaroo, we have then to consider the relations borne by its genera to the other genera of its family, the relations borne by its family to the other families of its order, and finally the relations borne by its order to the other orders of its class (the Mammalia)—that class which includes within it all other beasts whatever, and also man.
In the first place, it may be observed, there are many species of kangaroos, arranged in some four genera; but the true kangaroos form a genus, Macropus, which is very nearly allied to the three other genera. 2. Dorcopysis, with a very large first back tooth. 3. The tree kangaroos (Dendrolagus), which frequent the more horizontal branches of trees, have the fore-limbs but little shorter than the hind-limbs, and inhabit New Guinea; 4. The rat-kangaroos (Hypsiprymnus) which have the first upper grinding-tooth large, compressed, and with vertical grooves.
Fig. 6.—Skull of a Rat-Kangaroo (Hypsiprymnus).
These four genera together constitute the kangaroo's family, the Macropodidæ, the species of which all inhabit Australia and the islands adjacent, but are found nowhere else in the world.
The species agree in having—
1. The second and third toes slender and united in a common fold of skin.
These five characters are common to the group, and do not co-exist in any other animals. They form, therefore, the distinguishing characters of the kangaroo's family. This family, Macropodidæ is one of the six other families which, together with it, make up that much larger group, the kangaroo's order. As was just said, to understand what a kangaroo is, we must know "what are the relations borne by his family to the other families of its order;" and accordingly it is needful for our purpose to take at least a cursory view of those other families.
There is a small animal, called a bandicoot (Fig. 7), which, in external appearance, differs very plainly from the kangaroo, but resembles it in having the hind-limbs longer than the fore-limbs, and also in the form of its hind-feet, which present a kangaroo structure, but not carried out to such an extreme degree as in the kangaroo, and therefore approximating more to the normal type of foot, there being a rudimentary inner toe and a less preponderant fourth toe; the second and third toes, however, are still very small, and bound together by skin down to the nails. In the fore-foot, on the contrary, there is a deficiency, the outer toes being nailless or wanting. The cutting-teeth are more numerous, these being I 10
This little creature is an example of others, forming the family Peramelidæ—a family made up of creatures none of which much exceed the hare in size, and which, instead of feeding on vegetable substances (as do the kangaroos), eat insects, for which food they are well adapted by the sharp points and ridges which may be seen on their back teeth.
Fig. 7.—Long-nosed Bandicoot (Perameles).
One member of this family, Chæropus (Fig. 8), is very exceptional in the structure of its hind-feet, which out-kangaroo the kangaroo in the
minuteness of all the toes but the fourth, upon which alone the creature walks, while its front-feet are each reduced to two functional digits.
No other known beast besides walks upon a single toe in each hind-foot, save the horse family (horses, asses, and zebras), and they walk upon a different one, namely, that which answers to our middle-toe, while Chæropus walks on the next outer one or fourth. No known beast besides Chæropus walks upon two toes in each foot, save hoofed creatures, such as the ruminants and their allies; but in them it is the third and fourth toes that are used, while in Chæropus it is the second and third toes.
Another animal, called a phalanger (of the genus Phalangista) is a type of a third family of the kangaroo's order, the Phalangistidæ, a family made up of creatures which live in trees and are nocturnal in their habits, feeding upon fruits and leaves. Here we find the limbs of nearly equal length. Once more we have I 6⁄2, and we still have the second and third toes united in a common fold of skin; but the inner-most toe (that answering to our great-toe) is not only largely developed, but is like that of the apes, directed outward, and capable of being opposed to the other toes, as our thumb can be opposed to our fingers.
Fig. 9.—The Koala (Phascolarctus).
Some of these creatures have prehensile tails. Others have the skin of the flanks enlarged so as to serve them as a parachute in their leaps, whence they are called "flying opossums," just as squirrels, similarly provided, are called "flying" squirrels.
There are two very aberrant members of this family. One, the koala. Fig. 9. (Phascolarctus), called the native bear or native sloth, is devoid of any tail.
The other, Tarsipes, but little bigger than a mouse, has a long and pointed muzzle, and its teeth are reduced to minute pointed processes, few in number, 6—6/5—5, situated far apart in each jaw.
Fig. 10.—Cuscus Orientalis.
The genus Cuscus, closely allied to Phalangista, is found in New Guinea and the adjacent islands to Timor (Fig. 10).
Fig. 11.—The Wombat (Phascolomys).
Another animal, the wombat, Fig. 11 (Phascolomys), forms by itself a distinct family, Phascolomyidæ. It is a burrowing nocturnal animal, about the size of a badger, with rudimentary tail and peculiar feet and teeth.
We still find the second and third toes bound together, limbs of equal length, and all the five toes of the fore-foot with claws (as in the last family), but the great-toe is represented by a small tubercle, while the cutting teeth are 2/2, growing from persistent pulp through life, as in rats, squirrels, and Guinea-pigs (Fig. 12).
Fig. 12.—Teeth of the Wombat.
We may now pass to a very different family of animals belonging to the kangaroo's order. We pass, namely, to the Dasyuridæ, or family of the native cat, wolf, and devil, so named from their predatory or fierce nature. They have well-developed eye-teeth (or canines), and back teeth with sharp cutting blades, or bristling with prickly points. The second and third toes are no longer bound together; and while there are five toes with claws to each fore-foot, the great-toe is either absent altogether or small. The cutting teeth. Fig. 13, are 8/6
Fig. 13.—Teeth of Dasyurus.
and the tail is long and clothed with hair throughout. Some of these animals are elegantly colored and marked, and all live on animal food. This form (belonging to the typical genus Dasyurus, which gives its name to the family) may be taken as a type; but two others merit notice.
The first of these is Myrmecobius Fig. 14, from Western Australia, remarkable for its number of back teeth, 8—8/9—9' and for certain geographical and zoölogical relations, to be shortly referred to. With respect to this creature, Mr. Gilbert has told us: "I have seen a good deal of this beautiful little animal. It appears very much like a squirrel when running on the ground, which it does in successive leaps, with its tail a little elevated, every now and then raising its body, and resting on its hind-feet. When alarmed, it generally takes to a dead tree lying on the ground, and before entering
the hollow invariably raises itself on its hind-feet, to ascertain the reality of approaching danger. In this kind of retreat it is easily captured, and when caught is so harmless and tame as scarcely to make any resistance, and never attempts to bite. When it has no chance of escaping from its place of refuge, it utters a sort of half-smothered grunt, apparently produced by a succession of hard breathings."
Fig. 15.—Skull of Myrmecobius.
The other member of the family Dasyuridæ, to which I call the reader's attention, is a very different animal from the Myrmecobius. I refer to the largest of the predatory members of the kangaroo's order; namely, to the Tasmanian wolf. It is about the size of the animal after which it is named, and it is marked across the loins with tiger-like, black bands (Fig. 16). It is only found in the island of Tasmania, and will probably very soon become altogether extinct, on account of its destructiveness to the sheep of the colonists. Its teeth have considerable resemblance to those of the dog, and it differs from all other members of the kangaroo's order, in that mere cartilages represent those marsupial bones which every other member of the order unquestionably possesses.
Fig. 16.—Tasmanian Wolf (Thalacinus Cynocephalus).
The last family of the kangaroo's order consists of the true opossum, which (unlike all the animals we have as yet passed in review) inhabits not the Australian region, but America only.
These creatures vary in size from that of the cat to that of the rat.
They are called Dldelphidæ, and agree with the Dasyuridæ in having well-developed canine teeth and cutting back teeth (Fig. 17); in
Fig. 17.—Teeth of Opossum (Didelphys).
having the second and third toes free, and five toes to the fore-foot. But they differ in that
Cutting-teeth 10/8 (more than in any other animal).
One of them is aquatic in its habits and web-footed. Such are the very varied forms which compose the six families which together make up the kangaroo's order, and such are the relations borne by the kangaroo's family to the other families of the kangaroo's order.
But, to obtain a clear conception of the kangaroo, we must not rest content with a knowledge of its order considered by itself. But we must endeavor to learn the relation of its order to the other orders of that highest class of animals to which the kangaroo and we ourselves both belong, namely, the class Mammalia which class, with the other classes, birds, reptiles, and fishes together, makes up the back-boned or vertebrate primary division of the whole animal kingdom,
What, then, is the relation of the kangaroo's order—the Marsupialia—to the other orders of the class Mammalia?
Now, these orders are:
1. The order which contains man and apes.
Besides three orders of aquatic beasts (seals, whales, and the manatee order), with which we need not be now further concerned.
Fig. 18.—The Yapock (Chironectes).
Now, in the first place, very noticeable is the much greater diversity of structure found in the kangaroo's order than in any other order of mammals. While each of the latter is of one predominate type of structure and habit, we have found in the marsupials the greatest diversity in both.
Some marsupials are, we have seen, arboreal, some are burrowing, some flit through the air, while others range over and graze upon grassy plains. Some feed on vegetable food only, others are as exclusively insectivorous or carnivorous, and their teeth vary much in number and structure. Certain of my readers may wonder that such diverse forms should be thus grouped together, apart from the other mammals. At first sight it might seem more natural to place together flying opossums with flying squirrels;' the native sloth with the true sloth; the dog and cat-like opossums with the true dogs and cats; and, lastly, the insectivorous marsupials with the other insectivora.
As to the kangaroos themselves, they might be considered as approximating in one respect to the Ruminants, in another to the Rodents.
We have seen that even in Captain Cook's time its resemblance to the jerboa forced itself into notice. And, indeed, in this jerboa (and its first cousin, the alactaga) we have the same or even a relatively greater length of hind-limb and tail, and we have the same jumping mode of progression.
Again, in the little jumping insectivorous mammal, the shrew (Macroscelides), we meet with excessively long hind-limbs and a jumping habit. More than this: if we examine its teeth, we find both in the upper cutting teeth and in the back teeth great resemblance to those of the kangaroo. And yet there is no real affinity between the kangaroo and such creatures, any more than there is between a non-marsupial truly carnivorous beast and a marsupial carnivore. Indeed, both myself and ray readers are far more like the jerboa or weasel than either of the latter is like to any marsupial animal.
The fact is, that all these so varied marsupial forms of life possess in common certain highly-important characters, by which they differ from all other mammals. These characters, however, mainly relate to the structure of their reproductive organs, and could not be here detailed without a long preliminary anatomical explanation; but, as to the great importance of these characters, naturalists are agreed.
Among the characters which serve to distinguish the marsupials, there are two to which I have already called attention in describing the kangaroo; namely, the marsupial bones and the inflected angle of the lower jaw.
Every mammal which has marsupial bones has the angle of its jaw inflected, or else has no angle to its jaw at all; while every animal which has both marsupial bones and an inflected jaw-angle possesses also those special characters of the reproductive system which distinguish the marsupials from all other mammals.
Thus it is clear we have at least two great groups of mammals. One of them—the non-marsupials—contains man; the apes; bats; hedgehog-like beasts (shrews, moles, etc.); cats, dogs, bears, etc.; hoofed beasts; edentates; rodents, and also the aquatic mammals. And this great group, containing so many orders, is named Monodelphia. The other great groups consist of all the marsupials, and no others. It consists, therefore, of the single order, Marsupialia, and is called Didelphia.
Another group of mammals is made up of two genera only—the duck-billed platypus, or Ornithorhynchus, and the Echidna, two most interesting forms, but which cannot be further noticed here. They form, by themselves, a theme amply sufficient for an article, or even half a dozen articles.
As to its zoölogical relations, then, we may say that the kangaroo is a peculiarly modified form of a most varied order of mammals (the Marsupials), which differ from, all ordinary beasts (and at the same time differ from man) by very important anatomical and physiological characters, the sign of the presence of which is the coexistence of marsupial bones with an infected angle of the lower jaw.
We may now proceed to the next subject of inquiry, and consider the space relations (that is, the geographical distribution) of the kangaroo, its family, and order. I have already incidentally mentioned some countries where marsupials are found, but all of those were more or less remote. To find living, in a state of nature, any member of the kangaroo's order, we must at least cross the Atlantic.
When America was discovered by the Spaniards, among the animals found there, and afterward brought over to Europe, were opossums, properly so called—marsupials, of the family Didelphidæ, which extend over the American Continent, from the United States to the far South. These creatures were the first to make known to Europeans that habit of sheltering the young in a pouch which exists in the kangaroo, and which habit has given the name Marsupialia to the whole order. But, though this habit was duly noted, it is not strange that (being the only pouched forms then known) the value of the peculiarity should have been under-estimated. It is not strange that they should have been regarded as merely a new kind of ordinary flesh-eating beasts, since in the more obvious characters of teeth and general form they largely resembled such beasts. Accordingly even the gi-eat Cuvier, in the first edition of his "Règne Animal," made them a mere subdivision of his great order of flesh-eating mammals.
But, to find any other member of the kangaroo's order (besides the Didelphidæ), in a state of nature, we must go much farther than merely across the Atlantic; namely, to Australia or the islands adjacent to it, including that enormous and unexplored island, New Guinea, which has recently attracted public attention through the published travels of a modern Baron Munchausen.
To return, however, to our subject. To find marsupials at all, we have, as we have seen, to go to the New World. To find nearer allies of the kangaroo, we must go to the newest world, Australia; newest because, if America merited the title of new from its new natural productions as well as its new discovery, Australia may well claim the superlative epithet on both accounts. We have found an indication, in the name Botany Bay, of the interest excited in the mind of Sir Joseph Banks by the new plants as well as by the new animals of Australia. And, indeed, its plants and animals do differ far more from those of the New World (America) than do those of America from those of the Old World.
Marsupials, in fact, are separated off from the rest of their class—from the great bulk of mammals—the Monodelphia—no less by their geographical limits than by their peculiarities of anatomical structure.
And these geographical limits are at the same time the limits of many groups of animals and plants, so that we have an animal population (or fauna) and a vegetable population (or flora) which are characteristic of what is called the Australian region—the Australian region, because the Australian forms of life are spread not only over Australia and Tasmania, but over New Guinea and the Moluccas, extending as far northwest as the island of Lombok, while marsupials themselves extend to Timor.
In India, the Malay Peninsula, and the great islands of the Indian Archipelago, we have another and a very different fauna and flora—those, namely, of the Indian region, and Indian forms of life extend downward southeast as far as the island of Bali. Now, Bali is separated from Lombok by a strait of but fifteen miles in width. But that little channel is the boundary-line between these two great regions—the Australian and the Indian. The great Indian fauna advances to its western margin, while the Australian fauna stops short at its eastern margin.
The zoölogical line ofwhich passes through these straits is called "Wallace's line," because its discovery is due to the labors of that illustrious naturalist, that courageous, persevering explorer, and most trustworthy observer, Alfred Wallace, a perusal of whose works I cordially recommend to my readers, since the charm of their style is as remarkable as is the sterling value of their contents. Mr. Wallace pointed out that not only as regards beasts (with which we are concerned to-day), but that also as regards birds, these regions are sharply limited. "Australia has," he says, "no woodpeckers, no pheasants—families which exist in every other part of the world; but instead of them it has the mound-making brush-turkeys, the honey-suckers, the cockatoos, and the brush-tongued lories, which are found nowhere else upon the globe."
All these striking peculiarities are found also in those islands which form the Australian division of the archipelago, while in those islands which belong to its Indian division these Australian birds have no place.
On passing from the island of Bali to that of Lombok, we cross the division between the two. "In Bali," he tells us, "we have barbets, fruit-thrushes, and woodpeckers, while in Lombok these are seen no more; but we have abundance of cockatoos, honey-suckers, and brush-turkeys, which are equally unknown in Bali, or any island farther west."
As to our second point, then—the geographical relations of the kangaroo—we may say that the kangaroo is one of an order of animals confined to the Australian region and America, the great bulk of which order, including the kangaroo's own family, Macropodidæ, is strictly confined to the Australian region. We may further add that in the Australian region ordinary beasts (Monodelphia) are entirely absent, save some bats and a rat or two, and the wild-dog or dingo, which was probably introduced there by man himself.
There only remains, then, for us to inquire, lastly, what relations with past time may be found to exist on the part of the kangaroo's order or of the kangaroo itself. Now, in fact, these relations are of considerable interest. I have spoken of Australia as, what in one sense it certainly is, the newest world, and yet the oldest world would, in truth, be an apter title for the Australian region.
In these days we hear much of "survivals," as the two buttons behind our frock-coats are "survivals" of the extinct sword-belt they once supported, and the "Oh, yes! oh, yes! oh, yes!" of the town-crier is a "survival" of the former legal and courtly predominance of the French language among us. "Well, in Australia we have to-day a magnificent case of zoölogical survival on the largest scale. There, as has already been said, we find living the little Myrmecobius, which represents before our eyes a creature living in the flesh to-day, which is like other creatures which once lived here in England, and which have left their relics in the Stonesfield oolite, the deposition of which is separated from our own age by an abyss of past time not to be expressed by thousands of years, but only to be indicated in geological language as the Mesozoic period—the middle of the secondary rocks.
But Australia presents us with a yet more interesting case of "survival." Certain fish-teeth had from time to time been found in deposits of oolitic and triassic date, and the unknown creature to which they once belonged had received the name of Ceratodus. Only five years ago this animal, supposed to have been extinct for untold ages, was found still living in Queensland, where it goes by the name of "flat-head." It is a fish of somewhat amphibious habits, as at night it leaves the brackish streams it inhabits, and wanders among the reeds and rushes of the adjacent flats. The anatomy of this animal has been carefully described for us by Dr. Günther.
We have, then, in Australia what may be termed a triassic land, still showing us in life to-day the more or less modified representations of forms which elsewhere have long since passed away from among us, leaving but rare and scattered fragments—relics "sealed within the iron hills."
No member of the Australian families of the kangaroo's order has left its relics in European strata more recent than the secondary rocks. But the American family, Didelphidæ, is represented in the earliest Tertiary period by the remains of an American form (a true opossum) having been found by Cuvier in the quarries of Montmartre. He first discovered a lower jaw, and, from its inflected angle, concluded that it belonged to a marsupial animal, and that therefore marsupial bones were hidden in the matrix. Accordingly he predicted that such bones would be found; and, proceeding to remove the enveloping deposit with the greatest care, he laid bare before the admiring eyes of the bystanders the proof of the correctness of his prediction. It is noteworthy, however, that, had this fossil been that of an animal like the Tasmanian wolf, he would have been disappointed, as, though marsupial, it has, as has been already said, not marsupial bones, but cartilages.
But relics of creatures more closely allied to the kangaroo existed in times ancient historically, though, geologically speaking, very recent. Just as in the recent deposits of South America we find the bones of huge beasts, first cousins to the sloths andwhich live there now, so in Australia there lived beasts having the more essential structural characters of the kangaroo, yet of the bulk of the rhinoceros. Their bones and teeth have been found in the tertiary deposits of Australia, They have been described by Prof. Owen, and are now to be seen preserved in the British Museum and that of the Royal College of Surgeons. It may be that other fossil forms of the middle mesozoic or even of triassic times may, so some believe, have belonged to creatures of the kangaroo's family; but at least there is no doubt that such existed in times of post-tertiary date.
As to our third point—the geological relations of the kangaroo—we may say, then, that "the kangaroo is one of an order of animals which ranged over the Northern Hemisphere in triassic and oolitic times, one exceptional family lingering in Europe to the Eocene period, and in America to the present day. That the kangaroo itself is a form certainly become fossil in its own region, where, in times geologically recent, creatures allied to it, but of vastly greater bulk, frequented the Australian plains."
We may now, then, proceed to answer finally the question, "What is a kangaroo?" We may do so because the meaning of the technical terms in which the answer must necessarily be expressed (if not of undue length) has been now explained, as far as space has allowed.
We may say, then, that "the kangaroo is a didelphous (or marsupial) mammal, of the family Macropodidæ; an inhabitant of the Australian region and connected as respects its order with triassic times, and possibly even as regards its family also, though certainly (as regards the latter) with the time of the post-tertiary geological deposits.
We have seen what are didelphous and what are monadelphous mammals; what are the respective values of the terms "order," "family," and "genus," and also in what respect the kangaroo differs from the other families of the marsupial order. We have also become acquainted with the distribution of organic life now and with the interrelations of different geological strata, as far as those phenomena of space and of time concern our immediate subject.
By becoming acquainted with these matters, and by no other way, is it possible to give an intelligent answer to the question, "What is a kangaroo?"—Popular Science Review.