Pygmy Possums (Burramyidae)

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Pygmy possums

(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

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 sub-species 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

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

Habitat

Pygmy possums generally occur in wet sclerophyll or eucalypt 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 (300m). 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

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 Burramys 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

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.

Species accounts

List of Species

Eastern pygmy possum
Little pygmy possum
Mountain pygmy possum

Eastern pygmy possum

Cercartetus nanus

taxonomy

Cercartetus nanus (Desmarest, 1818), Tasmania, Australia. Two subspecies.

other common names

French: Phalanger-loir de l'Est; German: Östlicher Bilchbeutler.

physical characteristics

Length 7–7.8 in (18–20 cm). Brownish fur with gray belly. Base of tail thickened with storage fat. Tongue long, brush-tipped.

distribution

East and southeast of Australia, and Tasmania.

habitat

Heathland and dry and wet sclerophyll forest.

behavior

Mostly solitary. Constructs spherical nests of leaves and bark in tree-hollows.

feeding ecology and diet

Feeds on nectar, pollen, and insects.

reproductive biology

One to three young, twice per year. May be promiscuous or polygamous.

conservation status

Not threatened.

significance to humans

None known.

Little pygmy possum

Cercartetus lepidus

taxonomy

Cercartetus lepidus (Thomas, 1888), Tasmania, Australia.

other common names

French: Phalanger-loir mineur; German: Zwergbilchbeutler.

physical characteristics

Length 5 in (13 cm); 0.2–0.3 oz (6–9 g). Grayish brown with belly almost white.

distribution

Tasmania, Kangaroo Island, and northwestern Victoria.

habitat

Dry sclerophyll forests and mallee shrubland.

behavior

Constructs nests in tree-hollows, in wall cavities, under turf, or in birds' nests.

feeding ecology and diet

Insectivorous and carnivorous; preys even on lizards.

reproductive biology

Nothing is known.

conservation status

Not threatened, but rare throughout its range.

significance to humans

None known.

Mountain pygmy possum

Burramys parvus

taxonomy

Burramys parvus Broome, 1896, New South Wales, Australia.

other common names

French: Souris-oppossum de montagne; German: Bergbilchbeutler.

physical characteristics

Length 9–11.4 in (23–29 cm); 1–2.1 oz (30–60 g), up to 2.8 oz (80 g) when fat is stored.

distribution

Two small, isolated areas in Victoria, Australia.

habitat

Alpine meadows and rocky, boulder-strewn areas with heathland vegetation.

behavior

Nocturnal, spending day in nests in crevices, under rocks, etc. Periods of torpor in winter of up to 20 days or more; female social system is gregarious, possibly kin-related; males also possibly non-solitary, but in different habitat.

feeding ecology and diet

Omnivore, with heavy reliance on one moth species and seeds.

reproductive biology

Four young born after 12–16 days of gestation, leave the pouch after about three weeks, and are adult sized in three to four months. Probably polygamous.