Monotypic Species - The Musky Rat-Kangaroo
The musky rat kangaroo (Hypsiprymnodon moschatus) is a marsupial. This recent classification into the genus Hypsiprymnodon means it is now the only extant species. It is an example of a monotypic genus along with such examples as the bison, numbat, pronghorn and African painted dog.
The young of the marsupial is born in a very underdeveloped state and continues to grow and develop in a pouch. Generally the size of a jellybean (in this case a very small jellybean!), the baby claws its way to the pouch, clambers inside and attaches itself to a nipple. It is naked and blind at birth but continues its development in the pouch.
The musky rat kangaroo is the smallest of all kangaroos and one of only two that are strictly diurnal (active during the day). It is the smallest macropod that is quadrupedal and diurnal.
It differs from other kangaroo species by:
- having a bounding rather than a hopping gait
- having a tail that curls round to carry nesting material
- usually having two offspring at a time.
They belong to the same family as the potoroos and bettongs. Kangaroos and possums were related way back in the beginnings of evolution but have lost most of their similarities. However, like the possum, the musky rat kangaroo retains a great toe or hallux on the hind feet, giving it five toes on the hind feet. This mobile toe enables it to climb along fallen branches and logs. The musky rat kangaroo also shares with possums a series of grooves on the foot pads which help with gripping.
The musky rat kangaroo is restricted to the tropical rain-forests of north-eastern Australia. It is found in the lowlands and highlands to about 1200 metres.
Its native habitat is the floor of tropical rain-forests. It prefers the damper areas near creeks and rivers.
The musky rat kangaroo is about the size of a bandicoot or a large guinea pig. The head and body combined are about 230mm long. It weighs around 500 grams which is a bit more than half the next largest-in-size macropod. The tail is completely bare and scaly, with the appearance of polished leather. The female is slightly smaller than the male.
The pelage is a chocolate brown with a grey brown head. Unlike kangaroos it does not use the tail for support but carries the tail stretched out clear of the ground when it travels.
It is generally a solitary animal, terrestrial and frugivorous, active during most of the day but resting through the night, often under the roots of trees. It may form a nest from dried leaves and fern which it may site in the midst of a vine.
Although the hind legs are longer than the front legs, it does not hop like the kangaroo. Rather it moves in a slow bunny-hop movement by bringing the hind legs forward together. When travelling at speed the hind legs are moved forward outside the forelegs.
The musky rat kangaroo has a simple digestive system and cannot digest structural carbohydrates in plants as well as some other macropod species. It feeds mainly on fruits and seeds, some types of fungi and small invertebrates. At least 44 species of plants are ingested. Fleshy flowers from vines, twigs, leaves, lichen and soft inner bark from trees all form part of its diet. It turns over leaf litter to find invertebrates, fungi and seeds.
The actual kernel of the seed is eaten as well as the fleshy part. It even picks out fruit kernels from the droppings of the cassowary. It picks up food in the mouth, sits back on its rump in a hunched position then holds the food in its paws while it eats.
Breeding depends to some degree on availability of food. While this is a common practice among fruit-eaters it is not seen in any other potoroid. Delayed gestation (embryonic diapause) takes place during lactation. This species is sexually mature at 18 to 21 months and they breed for about 2 to 3 years. After a few days of courtship, two young are born with both usually surviving.
The testes of the male swell dramatically between September and October, contracting again between March and May. When in breeding condition, the male is more nervous and aggressive.
The young are born from February to April. Gestation lasts 7 months and the young are in the pouch until October. Although this is a time of limited food resources, there is also little demand by the tiny babies. By the time the young are ousted from the pouch, there is plenty of fruit available. The young stay at the nest gradually exploring further afield and by the time they are weaned in January they are completely self-sufficient. The lifespan is at least four years.
The musky rat kangaroo is listed as 'of least concern'. The species is an important dispersal agent for plants in the rainforest.