Burramyidae

Class Mammalia Order Diprotodontia Family Burramyidae

Thumbnail description

Small omnivores/insectivores, characterized by low-crowned molars with rounded cusps, reduced premolars, and reduced digital pads

Size

Head and body length 2.7-5 in (7-13 cm), tail 1.5-6.3 in (4-16 cm); weight 0.2-1.4 oz (6-40 g)

Number of genera, species

2 genera; 5 species

Habitat

Forests, woodlands, and subalpine meadows

Conservation status

Endangered: 1 species

Distribution

Australia and New Guinea

Distribution

Australia and New Guinea

Evolution and systematics

Fossils of pygmy possums have been found in central Australia, northern Queensland, and western Victoria, since the beginning of the Miocene (i.e., approximately 20-25 million years ago). They were mostly associated with rainforest habitats. The genus Burramys seems to have remained mostly unchanged since these early forms, thus forming a true living fossil. The family is most closely related to Acrobatidae. The burramyid family contains two genera, Burramys with only one species (B. parvus) and possibly two living subspecies, and Cercartetus with four species, three of which have two subspecies each. Burramys parvus, the mountain pygmy possum, certainly is one of the most exciting discovery stories of all mammals. It was first described in 1895, based on several fragments of skulls and jaws from a cave in New South Wales. Its long, blade-like (sectorial) premolar immediately caught the zoologists' attention, as similar teeth had also been described for several rat-kangaroos (not to mention a truly fossil order, Multituberculata). For several decades, it was undecided whether this mysterious fossil belonged to the rat-kangaroos or to the possum group. In 1956, Dr. David Ride firmly stated that Burramys was supposed to

A long-tailed pygmy possum's tail (Cercartetus caudatus) can be more than 6 in (15.1 cm) long. (Photo by Pavel German. Reproduced by permission.)

found, in fossil records, in several parts of eastern and central Australia.

Habitat

Pygmy possums generally occur in wet sclerophyll or eu-calypt forests. Cercartetus caudatus, the long-tailed pygmy possum, the only tropical species, lives in the mountain rainforests of New Guinea's Central Cordillera above 4,900 ft (1,500 m), in a small area near Townsville in tropical Queensland, and also in mountainous areas above 985 ft (300 m). In New Guinea, specimens are often trapped on the ground in subalpine grasslands above the tree line. Extended torpor (up to six days duration in C. lepidus) has been described in all species, either during winter or as daily torpor.

Behavior

All species are nocturnal, and all routinely construct nests of leaves, bark, and other plant material, in tree hollows or as independent structures. Burramys parvus is terrestrial, living in alpine meadows and boulder fields. All the other species are arboreal, using their long prehensile tails as a support or for balance when climbing small branches. It is appropriate to distinguish between the two genera, as they differ in many aspects. In fact, they are only united in one family based on anatomical and morphological characteristics. Mountain

The eastern pygmy possum (Cercartetus nanus) feeds on nectar and pollen with its brush-tipped tongue. (Photo by Pavel German/Nature Focus, Australian Museum. Reproduced by permission.)

The eastern pygmy possum (Cercartetus nanus) feeds on nectar and pollen with its brush-tipped tongue. (Photo by Pavel German/Nature Focus, Australian Museum. Reproduced by permission.)

be an extinct possum. However, 11 years later, a live specimen was caught in a skiing hut on Mount Hotham in Victoria, far above the snow line.

Physical characteristics

The pygmy possums closely resemble small dormice of the Northern Hemisphere, such as the hazel mouse (Muscardinus avellanarius). Species range in size from 2.3-2.7 in (6-7 cm) and 0.2 oz (7 g) in the smallest species, Cercartetus lepidus, to the largest Burramys parvus with 4.3 in (11 cm) and 1.4 oz (40 g). Coat colors are mostly brownish on the upper, cream-colored to grayish on the underside. Some species store fat in the tails.

Distribution

The range of the family as a whole covers parts of Australia (the southeast, including Tasmania, the southern west, and a small part of the Queensland wet tropics) and the central mountain range of New Guinea. Burramys has been

A long-tailed pygmy possum (Cercartetus caudatus) showing the dark rings around its eyes. (Photo by Pavel German/Nature Focus, Australian Museum. Reproduced by permission.)
The western pygmy possum (Cercartetus concinnus) is mostly arboreal. (Photo by Robert Valentic/Nature Focus, Australian Museum. Reproduced by permission.)

pygmy possums are only found in two small areas between 4,265 and 7,300 ft (1,300 and 2,230 m) on the peak of Mt. Kosciusko, the highest mountain in Australia. Its habitat mostly is subalpine, shrubland, and meadows. Burramys has to cope with at least three months of snow cover, during which time it tends to live under the snow, climbing within and between rock crevices, or climbing into bushes to collect seeds and berries. Burramys also stores fat under its skin, and develops a thick fur in autumn. The heaviest animal ever found in autumn weighed 3 oz (82 g). Adults tend to enter hibernation earlier than juveniles, and can remain torpid for periods of up to 20 days. Another means of energy conservation is communal nesting. These nests are normally of either all males or all females, and can be found throughout the year, except when females breed. The social organization of Bur-ramys is more complex than expected in such a small mammal. Up to 10 females (probably related kin such as mother with daughters, granddaughters, etc.) occupy communal, overlapping home ranges. Female ranges are higher up in the mountains, in more productive areas. Males visit these female ranges only briefly for mating, and emigrate again after breeding season, returning to their own ranges in lower less productive areas of their habitat. Males are quite tolerant of each other, both in captivity and even during breeding times. It is not clear whether females evict males, or whether they emigrate on their own, but the resulting social/mating system is one of female communal resource defense and male polygamy. Data on population structure and longevity are in accordance to trapping data, which is highly female-biased, and show that females live for up to 11 years, while males live only up to four years.

Feeding ecology and diet

Cercartetus caudatus is primarily insectivorous, but also can be found eating flowers and possibly plant exudates. Some species, particularly C. nanus, regularly visit flowering plants and feed on nectar and pollen predominantly. Others are more insectivorous or even kill small lizards. Mountain pygmy possums feed on seeds, fruit, insects, and other small invertebrates. In summer, the Bogong moth (Agrotis infusa) is of particular dietary importance. Burramys stores only hard seeds, nuts, etc., in the fall, while soft berries and fruits are eaten at once. All species are prey for owls, carnivorous marsupials, snakes, and feral cats.

Reproductive biology

Females have four teats. The mountain pygmy possum mother rears four young on her own, once per year. Most

The long-tailed pygmy possum (Cercartetus caudatus) eats nectar and insects. (Photo by Dick Whitford/Nature Focus, Australian Museum. Reproduced by permission.)
An eastern pygmy possum (Cercartetus nanus) holds on to a plant with its hand-like paws. (Photo by Pavel German. Reproduced by permission.)

possums are found in communal nests of up to five individuals. Females carry one to three young, and these remain in the pouch until they are 0.2 oz (7 g), which is remarkable considering the fact that the mothers themselves weigh only 0.5-0.8 oz (15-24 g). The young appear to become independent at a weight of above 0.35 oz (10 g). Breeding in this polygamous species occurs twice per year in Australia (January-February and August-November), indicated not only by the distribution of pouch-gravid females but also by a regression in size of testes in males.

Conservation status

Due to its very limited range, the mountain pygmy possum is classified as Endangered. Habitat fragmentation and disturbance are the most imminent dangers for its survival. However, two long-term threats must also be considered: Global warming could easily change its alpine habitat into less productive ones, and the population of Bogong moths depends on both the amount of rainfall as well as the preservation of their own habitats, which could be compromised by agricultural activities.

All the other species belonging to the genus Cercartetus are currently not threatened in status with regard to IUCN listings. However, C. lepidus is considered to be Vulnerable due to its contracted range.

Significance to humans

None known.

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