Musky rat-kangaroos

(Hypsiprymnodontidae)

Class Mammalia

Order Diprotodontia

Family Hypsiprymnodontidae

Thumbnail description
The one living species is a small, quadrupedally bounding animal with a sparsely haired tail, slender head, and dark chocolate-brown fur; the hindfoot has four toes; the third premolar is long and serrated ("sectorial")

Size
Head and body length, 5.9–10.6 in (15–27 cm); tail length 4.7–6.3 in (12–16 cm); weight, 12.6–24 oz (360–680 g)

Number of genera, species
1 genus; 1 species

Habitat
Tropical rainforest

Conservation status
Not threatened

Distribution
Tropical Queensland (Australia)

Evolution and systematics

The Hypsiprimnodontidae are considered to be the most basic group of Macropodoidea, on account of their simple stomach, remaining first toe, apparent inability to hop "kangaroo-like," regular twin births, etc. In skeletal morphology they share a number of characteristics with Potoroidae, i.e., large masseteric foramina, a blade-like structure of the third premolars, the presence of upper canines, and a confluence of the masseteric and inferior dental canals on their mandibles. The Hypsiprymnodontidae are separated from Potoroidae by the fact that they possess two (instead of one) lower incisors, and the fact that their squamosal bones are in broad contact with the frontals (this is similar to Macropodidae). On serological ground, all rat-kangaroos are closer to macropodids than to phalangerids, whereas their bunodont (rounded-cusp) molars resemble phalangerids more closely.

Hypsiprymnodontidae have been known in the fossil record since the Miocene. One species, Hyspiprymnodon bartholomai, from the early Miocene (approximately 20 million years ago), is very similar in shape and size to the living

species of musky rat-kangaroo, thus making the extant species a true living fossil. However, the most dramatic members of the family are certainly the extinct Propleopinae, the so-called giant rat-kangaroos. In the Pleistocene, some of them reached the size of a true kangaroo (up to at least 132 lb [60 kg]), and they were probably at least partially carnivorous. The size, wear, and position of their molars, their long, protruding, dagger-like incisors, and the comparatively small number of their remains in fossil deposits, all point to a position near the top of the food-chain. The smallest of these species, Ekaltadeta sina, reached 33–44 lb (15–20 kg), and is one of the oldest kangaroo species of all. The largest and youngest species, Propleopus oscillans, is a Pleistocene species whose last members probably became extinct about 10,000 years ago. Some researchers speculate that propleopines may have died out as recently as 6,000 years ago (which would mean that they survived until the dingo appeared).

The taxonomy for this species is Hypsiprymnodon moschatus Ramsay, 1876, Queensland, Australia.

Physical characteristics

The one extant species, Hypsiprymnodon moschatus, is quite easy to recognize. It has a slender head, with an almost "delicate" skull, a hairless rhinarium, and no concavity on the dorsal side. Its fur is soft and rufous-brown with gray underfur on the head. Forelimbs and hindlimbs are more equal in lengths than in potoroids (or macropodids), and the hindfoot has a claw-less, but prominent first digit, which can be opposed. They have striated pads and ceratinous scales on the palms of their hands and the soles of their feet. The animal is small, and males and females are of similar sizes. Females (18 oz/511 g) weigh slightly less than males (18.7 oz/529 g).

Distribution

The musky rat-kangaroo is found only in one small area of about 199 mi by 40 mi (320 km by 65 km), in northern Queensland. As far as is known, this range has not been any larger in historical time. All the extinct species also were rain-forest-species. However, as rainforest covered more of Australia in prehistoric times, their range also was larger.

Habitat

Musky rat-kangaroos are strictly confined to tall rainforests at all altitudes. They are most regularly observed in damp areas, around lakes, or near creeks and rivers. Though basically terrestrial, they are adept climbers, and can often be found on fallen branches, trees, or logs. The striated pads and ceratinous scales on their palms and soles help them climb. In a breeding colony in Pallarenda, near Townsville, animals were observed to climb up to heights of more than 6.6 ft (2 m). Musky rat-kangaroos construct nests, similar to potoroid nests, by collecting plant material, carrying it in their tails, and forming loose piles of leaves in clumps of vines or near root-buttresses. When disturbed, the animals usually retreat into more dense, shrubby vegetation, such as near the lakeshores, returning into the tall forest after the disturbance ceases.

Behavior

Musky rat-kangaroos seem to be basically solitary in the wild, though in captivity they can be kept in pairs, or one male can be kept with two or more females. However, it has been impossible to keep two or more males together, even in enclosures of 215 ft² (200 m²). In the wild, aggregations of up to three animals are sometimes seen feeding on fallen fruit. There is no evidence of territoriality. Descriptions of social behavior are almost nonexistent, except for some descriptions of body postures (standing in front of female, pawing her head, or lateral sinuous movements of the tails in male

courtship). Musky rat-kangaroo are exclusively diurnal, spending the night and the noontime in their nests.

Feeding ecology and diet

Food is located presumably by scent and retrieved from leaf litter with the forepaws. Fruits and nuts of rainforest trees (e.g., candlenut, Aleuntes moluccana; king palm, Archontophoenix alexandrae; and kelat or watergum, Eugenia kuranda) are eaten, as well as insects, earthworms, and other invertebrates. Shells of small nuts or exoskeletons of insects are crushed by pushing them deep into the mouth between the sectorial blades of the third premolars. The flesh of fruit is scraped off with the lower incisors. Due to the simple, sacciform forestomach, and the rather small hindgut and caecum, musky rat-kangaroos are most probably unable to digest allozymatically (i.e., by means of bacteria and other symbiontic organisms), unlike all other macropodoids. This means that they need to forage on low-fiber, easy-to-digest foods.

Reproductive biology

Courtship and mating seems to follow typical rat-kangaroo patterns, which are polygynous. The male rapidly chases the female, or blocks her way by standing in front of her, slashing his tail laterally in undulating movements and pawing her head. If the female is not yet receptive, she throws herself onto her side and vigorously kicks at the male with her hind-limbs. When she is more receptive, both animals stand erect and touch each other's face and neck with their forepaws. These courtship phases may last a few days and normally occur between February and July. Two young, occasionally triplets, are born, and twins are normally raised in their mother's pouch. After about 21 weeks the young leave the pouch, and mostly stay in the nest for several weeks. Only then do they follow their mothers in typical young-at-heel fashion, similar to other kangaroos. Females become sexually mature at just over one year of age.

Conservation status

Though not listed by the IUCN, the 1996 Action Plan from the IUCN's Australian Marsupial and Monotreme Specialist Group suggests that H. moschatus be listed as Lower Risk/Least Concern due to its restricted area of distribution, and the fact that its only habitat—closed, tall rainforest—is rapidly diminishing in Australia.

Significance to humans

None known.

Resources

Books

Archer, M., S. J. Hand, and H. Godthelp. Australia's Lost World: Prehistoric Animals of Riversleigh. Bloomington, IN: Indiana University Press, 2001.

Johnson, P. M. "Musky Rat-kangaroo." In The Australian Museum Complete Book of Australian Mammals, edited by R. Strahan, 179–180. Sydney, Angus & Robertson, 1995.

Kennedy, M., ed. Australasian Marsupials and Monotremes—An Action Plan for Their Conservation. Gland, Switzerland: IUCN, 1992.

Seebeck, J. H., and R. Rose. "Potoroidae." In Fauna of Australia. IB. Mammalia, edited by D. W. Walton and B. J. Richardson, 716–739. Canberra, Australian Government Publication Service, 1989.

Vickers-Rick, P., J. M. Monaglan, R. F. Baird, T. H. Rick, eds. Vertebrate Paleontology of Australasia. Melbourne: Pioneer Design, 1991.

Periodicals

Johnson, P. M., and R. Strahan. "A Further Description of the Musky Rat-kangaroo With Notes on Its Biology." Australian Zoologist 21 (1982): 27–46.

Schürer, U. "Das Moschusrattenkänguruh, Hypsiprymnodon moschatus—Beobachtungen im Freiland und im Gehege." Der Zoologische Garten N. F. 55 (1985): 257–267.

Wroe, S. "Killer Kangaroos and Other Murderous Marsupials." Scientific American 280 (1999): 68–74.

Udo Gansloßer, PhD