The Cambridge Natural History Part 10

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FIG. 69.--Vulpine Phalanger. _Trichosurus vulpecula._ 1/6.

SUB-FAM. 1. PHALANGERINAE.--The genus _Phalanger_ embraces five species, sometimes called by the generic name of _Cuscus_. They are largish animals with short ears; only the end of the tail is naked. Of these animals only one species is found in Australia itself, the rest inhabiting the islands lying to the north. The Spotted Cuscus, _Ph. maculatus_, is in spite of its vegetarian diet, and perhaps on account of its spots, spoken of as the "Tiger Cat." Mr. Aflalo remarks of it that though provided with a prehensile tail, it is little better as a climber than the tailless Koala.

_Trichosurus_, including the "True Phalangers," includes largish species, which can be distinguished from the last genus by a chest-gland similar to that which occurs in _Myrmecobius_ and some other Marsupials of the present group. There are but two species, which are purely Australian. The "Brush-tailed Opossum," _T. vulpecula_ (perhaps better known as _Phalangista_ {141} _vulpina_), like its American pseudo-namesake (a true Opossum, genus _Didelphys_), "plays 'possum" on occasions. The dental formula is I 3/2 C 1/0 Pm 2/3 M 4/4. The ears are shortish.

The Ring-tailed Phalangers, _Pseudochirus_, are more widely distributed than the last two genera; they range from Tasmania in the south to New Guinea in the north. They are not, however, ring-tailed, though the tip of the tail is generally white. As in the last genera, which have prehensile tails, the end of this appendage is naked. The mammae are four. The tooth formula is I 3/2 C 1/0 Pm 3/3 M 4/4. There are some ten species of the genus.

The Striped Phalanger, _Dactylopsila trivirgata_, is an animal about a foot long, whose ident.i.ty can be ascertained by its striped, black and white skin. It is an arboreal creature that lives apparently both on leaves and grubs like so many arboreal creatures of quite different groups--Squirrels, for instance, and New-World Monkeys. The tooth formula is I 3/3 C 1/6 Pm 3/2 M 4/4.

_Gymn.o.belideus leadbeateri_ is a small creature with a body 6 inches in length. It is restricted to the colony of Victoria. The general look is that of _Petaurus_; the ears are naked.

_Dromicia_ is a genus of Phalangers which although devoid of a parachute, such as is possessed by certain genera that will be considered immediately, is able to leap with great agility from branch to branch. The ears are large and thin and almost naked; the tooth formula is I 3/2 C 1/0 Pm 3/3 M 4/4. They are minute creatures, the longest measuring, with the tail, but 10 inches. Dormouse-Phalanger is a name sometimes given to them. There are four species, ranging from Tasmania to New Guinea. The name Dormouse as applied to the genus seems to be owing to the way in which they hold a nut in the paws when feeding. _D. nana_ is 4 inches long, with a tail of nearly the same length. It is thick at the base.

_Distaechurus_ is the last genus of non-flying Phalangers. Its name refers to the arrangement of the hairs on the tail, which are disposed on either side in a row like the vane of a feather. The tooth formula is I 3/2 C 1/0 Pm 3/2 M 3/3, very nearly as in _Acrobates_. The ears are as in that genus.

_Petaurus_ is the first genus of the Flying Phalangers, all of which are provided with a parachute-like expansion of the skin between the fore- and hind-limbs; the ears are large and naked; and the tooth formula is I 3/2 C 1/0 Pm 3/3 M 4/4. There are three {142} species of the genus, which extend through pretty well the entire Australian region. The term "flying"

as applied to these and the other "flying" genera is of course an exaggeration. The animals cannot fly upwards; they can only descend in a skimming fashion, the folds of skin breaking their fall. _P. breviceps_ is perhaps the best-known species. The body is 8, the tail 9 inches long.

_Petauroides_ seems to be chiefly distinguished from _Petaurus_ by the fact that, as in its ally _Dactylopsila_, the tail is partly naked terminally.

In _Petaurus_ and _Gymn.o.belideus_ the tail is bushy to the very end, including its extreme tip below.

A third genus of Flying Phalangers is the minute _Acrobates_, which has a distichous tail like that of _Distaechurus_. It is not more than 6 inches in length including the tail. As to these Flying Phalangers it is exceedingly instructive to observe that the same method of "flight" has been apparently evolved three times; for the three genera are each of them specially related to a separate type of non-flying Phalanger. The same observation can be made about the Flying Squirrels, _Anomalurus_ and _Sciuropterus_. The dental formula is I 3/2 C 1/0 Pm 3/3 M 3/3. The ears are thinly clad with hair. There are four teats.

SUB-FAM. 2. PHASCOLARCTINAE.--The Koala, or Native Bear, _Phascolarctos cinereus_, is the only representative of its sub-family. It is, like the Wombat, aberrant in the lack of an obvious tail. The absence of this appendage is curious in an arboreal creature whose near allies have a long and prehensile one. The structure of the Koala was investigated by the late Mr. W. A. Forbes.[89] There are some unexpected points of likeness to the Wombat: thus they agree in the absence of the tail, in the structure of the stomach, and in the great subdivision of the lobes of the liver. The brain, however, is smooth, and the caec.u.m is exceedingly large and complicated in structure, that of the Wombat being short. That both animals have cheek-pouches is perhaps due to similar habits of temporarily storing ma.s.ses of food. This animal has only eleven pairs of ribs. The tail has only seven or eight vertebra, and these have no chevron-bones.

A peculiarity of the skull is seen in the great size of the alisphenoid bulla, which is comparable in size and appearance with that of the Pig. As in the Kangaroos, the atlas is incomplete below. {143}

The tooth formula of the genus is I 3/1 C 1/0 Pm 1/1 M 4/(4 or 5). The additional lower molar seems to be exceptional, and has been found in one specimen only.

In the alimentary tract the most remarkable structure is the large intestine, which is very capacious for the first 28 inches or so of its course. This section of the colon is lined with rugae precisely like those which are found in the caec.u.m. These folds, which at first are some twelve in number, fuse lower down, and by the time that the colon approaches the external orifice are reduced to five. Similar folds, as already stated, occur in the caec.u.m, but do not extend as far as its blind end. The caec.u.m is proportionately and actually larger than in any other Marsupial. The gall-bladder is unusually elongated.

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FIG. 70.--Koala. _Phascolarctos cinereus._ 1/9.

The Koala is mainly crepuscular or nocturnal in its habits. It feeds so exclusively upon the leaves of the gum-tree (_Eucalyptus_) that it is impossible to keep the creature long in captivity in lands where that particular kind of food is not available.

The female, though she seems to bear but a single young one, which is carried on the back after the fashion of some Opossums, has two nipples.

The animal's slow habits seem to require a nocturnal and retired life. It is about as lethargic as the Sloth, and it is said to further resemble that animal in clinging firmly to a branch even after it is shot. {144}

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FIG. 71.--Wombat. _Phascolomys wombat._ 1/12.

SUB-FAM. 3. PHASCOLOMYINAE.--_Phascolomys_, the Wombat, is the only genus of this sub-family. This animal has the appearance of a heavily-built Marmot, like which it has a mere stump for a tail, and a pair of strong chisel-shaped and Rodent-like incisors, which, however, differ from those of Rodents in having a complete coating of cement. All the teeth of the animal are rootless, and there are no canines. The incisors have enamel on the front and lateral faces only. The dental formula is I 1/1 C 0/0 Pm 1/1 M 4/4. The affinities with other Diprotodont Marsupials are shown by the commencing syndactyly of the second and third toes. The rhinarium is naked or hairy. There is a rudimentary cheek-pouch, as in _Phascolarctos_. The Wombat has, like the Koala, and also the Beaver--which does away with some of the value of the comparison--a peculiar gland-patch in the stomach, a raised area of collected glands. In no other Marsupial is such a structure found, "whilst in the two forms under consideration its ident.i.ty is almost precise. That such a unique structure should have been independently developed in two forms unrelated to each other, appears to me to be in the highest degree improbable." This is Mr. Forbes' opinion. It might be strengthened by adding the observation that, as there are other points of likeness between the Wombat and the Koala, it seems more unlikely that a structure so nearly identical should have been twice {145} developed in two not very distant forms. As in the Kangaroos, the atlas is open below. _Ph.

ursinus_ has 15 ribs; the other species the normal (for Marsupials) 13.

Other points of likeness will be mentioned under the description of the Koala. These animals mainly feed upon roots; they live in companies in burrows. There are three species--_Ph. ursinus_, _Ph. latifrons_, and _Ph.

mitch.e.l.li_. _Ph. ursinus_ is Tasmanian in range, the other two species South Australian.

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FIG. 72.--Skull of Wombat. _Phascolomys wombat._ (Lateral view.) _ang_, Angular process; _cond_, condyle of mandible; _ex.oc_, exoccipital; _ext.aud_, opening of bony auditory meatus; _ju_, jugal; _lcr_, lachrymal; _max_, maxilla; _nas_, nasal; _p.max_, premaxilla; _sq_, squamosal; _ty_, tympanic. (From Parker and Haswell's _Zoology_.)

SUB-FAM. 4. TARSIPEDINAE.--The genus _Tarsipes_ ought perhaps to be removed from the present family. There is but a single species, which is a small creature of 7 inches in total length, of which the tail measures 4 inches.

The teeth are much dwindled, the formula being I 2/1 C 1/0 Pm 1/0 M 3/3 = 22. The lower incisors are proc.u.mbent. The lower jaw, moreover, has not the characteristic Marsupial inflection. The intestinal ca.n.a.l is without the caec.u.m present in the remaining Phalangeridae. It is a curious fact that this aberrant little Phalanger should come from Western Australia, like the even more aberrant _Myrmecobius_. Like the latter also, _Tarsipes_ has a long exsertile tongue, with which, however, it extracts honey from flowers.

Probably it also catches minute insects in the corollas of the flowers. It has been proved, in fact, that in captivity at any rate the animal is insectivorous; for it has been known to eat moths.

FAM. 3. EPANORTHIDAE.--The extinct Epanorthidae of {146} Patagonia are represented to-day by a small Marsupial which has been rediscovered within the last two or three years. This little animal, formerly called _Hyracodon_ (a pre-occupied name), is now termed _Caenolestes_, and is a native of Colombia and Ecuador. There are two species, and of these _C.

obscurus_ is called by the inhabitants "Raton runcho," which means opossum-rat. It lives apparently upon bird's eggs and small birds, though it belongs to the Diprotodont division of the Marsupials. _Caenolestes_, however, although diprotodont, has not the syndactylous character of the digits of the feet already referred to in the Kangaroos and their allies.

The pouch is small and rudimentary. The dent.i.tion is I 4/3 C 1/1 Pm 3/3 M 4/4 = 46, and the teeth are said by Mr. Thomas to be much like those of the Australian _Dromicia_.[90]

In the skull a peculiarity which does not bear upon its affinities to other Marsupials, but is still interesting, is mentioned by Mr. Thomas. The nasals are not sufficiently prolonged to meet the upper edge of the maxillae, and so a vacuity is left, as in the skulls of many Ruminants (_e.g._ the Sable Antelope). The palate is very imperfect; the foramina, which render it so, reach as far forward as the last premolar. The lower jaw has quite the appearance of that of a _Macropus_ or _Phalanger_, with long and forwardly projecting incisors.

EXTINCT DIPROTODONTS.--The great _Diprotodon_ is a creature with a skull a yard long, which must have been of the size of a large Rhinoceros. Though closely allied to _Macropus_, it seems that this great beast did not hop after the fashion of a Kangaroo, its limbs being of a more equal size than in the Kangaroo. Recently some further remains of _Diprotodon_ have been discovered in a lake known as Lake Mulligan, where they had apparently been bogged. Professor Stirling has contributed an account of these remains, which fills up a considerable gap in our knowledge. He has been able to state the structure of the fore- and hind-limbs. Both limbs are pentadactyle, the fingers of the fore-limb being approximately equal in length and general development. In the hind-limb the hallux is small, and consists of the metatarsal only. This bone is fixed in the position of "extreme abduction," and is suggestive of an arboreal limb. Digits two and three may have {147} been syndactylous, and the authors of the account[91]

of these bones think that the fourth toe may have shared in this syndactyly. The metatarsal of the fifth digit is enormously expanded at its edge, and seems to have furnished a strong support to the creature; this is also seen in the metacarpal of the fore-limb. Probably, therefore, _Diprotodon_ was quadrupedal in its mode of progression, with the emphasis laid upon the little finger and the little toe instead of, as in ourselves, the first toe. The hind-foot of the _Diprotodon_ could not be more unlike that of a Kangaroo than it actually is.

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FIG. 73.--_Diprotodon australis._ (After Owen.)

FIG. 74.--_Thylacoleo carnifex._ Side view of skull. (After Flower.)

Another giant among these Marsupials was the genus _Thylacoleo_, whose name was given to it by Sir Richard Owen on the view that it was a Marsupial Tiger. Sir W. Flower has, however, controverted this opinion, and the genus is in fact, in spite of its large size, closely allied to the Phalangers and {148} Cuscuses.[92] The dental formula is I 3/1 C 1/0 Pm 3/1 M 1/2; the last premolar is a great blade-shaped tooth like that of _Potorous_.

_Nototherium_ was a creature smaller than _Diprotodon_, but still of large size; it is believed to have been a burrowing creature, and to connect the Wombats with _Diprotodon_. More certainly allied to the existing Wombat was _Phascolonus_, a Wombat as big as a Tapir.

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FIG. 75.--_Nototherium mitch.e.l.li._ Side view of skull. 1/6. (After Owen.)

Of extinct American Diprotodonts the Epanorthidae, already referred to in connexion with the living _Caenolestes_, were the most prominent forms. The genus _Epanorthus_ occurs in the Santa Cruz formation of Patagonia, which is believed to be Miocene. The incisors are three in the upper jaw; and the single incisor of each ramus of the lower jaw is a great chisel-shaped, cutting instrument.

_Abderites_ is also typically Diprotodont by reason of the large projecting incisors of the lower jaw. It has a large cutting tooth in the lower jaw, which appears to be the last premolar, and is thus comparable to the great cutting tooth of the lower jaw and of the upper jaw of the extinct Phalanger, _Thylacoleo_. {149} It may also be comparable to the great premolar of such Mult.i.tuberculata as _Ptilodus_ and _Plagiaulax_. It is, moreover, marked with vertical grooves.

An interesting form, which is unfortunately but little known, is the Australian and Pleistocene genus _Triclis_, with one species, _T.

oscillans_. In having a minute canine tooth in the lower jaw it agrees with some Phalangeridae, and being otherwise closely allied to _Hypsiprymnodon_, it unites the Macropodidae with the Phalangeridae.

SUB-ORDER 2. POLYPROTODONTIA.

In this mainly carnivorous or insectivorous division of the Marsupials the incisors are four or five on each side of the upper jaw, and one or two fewer in the lower jaw. Figs. 76 and 77 ill.u.s.trate the Polyprotodont and Diprotodont dent.i.tions. The canines are those of flesh-eaters and so are the molars, being as a rule sharply cuspidate. As a rule, which has an exception in the Peramelidae, there is no syndactylism of toes in the hind-foot. This sub-order is at the present day Australian and American in its range.

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FIG. 76.--Front view of the skull of Tasmanian Devil (_Sarcophilus ursinus_), showing Polyprotodont and carnivorous dent.i.tion. (After Flower.)