(Pseudocheiridae)
Class: Mammalia
Order: Diprotodontia
Family: Pseudocheiridae
Thumbnail description
Medium-sized possums, most species rather slow-moving, with short limbs; their teeth, particularly molars, have selenodent (i.e., half-moon shaped) crests, ideal for cutting and grinding leaves; ears are small and furred, fur color is mostly brown or gray with the last part of the (prehensile) tail more or less hairless
Size
12.6–37.4 in (320–950 mm), 4.1–79.4 (115–2250 g)
Number of genera, species
6 genera; 16 species
Habitat
Forests and woodlands, suburban areas
Conservation status
Vulnerable: 3 species; Lower Risk/Near Threatened: 4 species; Data Deficient: 3 species
Distribution
New Guinea, Australia including Tasmania
Evolution and systematics
Pseudocheiridae are most closely related to Petauridae, and together they form a superfamily Petauroidea. Even though this superfamily is named after petaurids, the pseudocheirids are obviously the more primitive and generalized family. This is evident both from morphology and from paleontological data. Pseudocheirids have been found in very old Tertiary deposits. The oldest undoubtedly pseudocheirid known so far comes from the late Oligocene-middle Miocene, and those genera are already rather distinct from each other. Oligocene as well as Quaternary species have been found in several central Australian and Queensland records, which points to a wide-ranging distribution already there. These paleontological data, together with the fact that today only two genera (nine species) live in New Guinea, but six genera (seven species) live in Australia, suggest that the family had its origin in Australia and immigrated into New Guinea quite recently. Dental morphology of pseudocheirids is also considered rather primitive: The W-shaped molars are considered (Archer) as more primitive than the rounded cusps of petaurids. Even though koalas also have similar molar crowns, this is being regarded as a convergence due to leaf-eating. Both cytogenetic studies and albumin microcomplement fixation techniques have yielded quite clear-cut results recently concerning taxonomy within the family. No subfamily has been erected, but Hemibelideus and Petauroides are closely related to each other, and only distantly related to the rest. Petropseudes and Pseudochirops similarly are separate from the rest, but also with a certain distance between the two genera. Pseudochirulus, which now contains several species previously assigned to Pseudocheirus, also is an isolated genus. Some of the species (e.g., P. peregrinus, Pseudochirulus canescens) are subdivided into up to six subspecies, which is further evidence for both long isolation and old radiations.
Physical characteristics
The greater glider Petauroides volans is quite distinct from the rest of the family. It possesses a gliding membrane from elbows to lower legs similar but convergent to Petaurus spp., and a bushy tail. Its ears are large, the fur is long and woolly, and varies from white or gray to dark brown, sometimes with tail and body being in different colors. Its size puts it apart, with up to 37.4 in (95 cm) head-to-tailtip, and a weight of 32.8–42.3 oz (930–1,200 g). The rest of the family, in external appearance is rather similar. All have short, stocky limbs, short round ears, and tails that are bare at the lower side at least about the final third of their lengths. Many species have dorsal stripes, though these are not always clearly seen when the fur itself is rather dark. Fur colors differ from light gray/cream, to orange, to dark brown. One species is greenish due to a mix of yellow, black, and white hairs. Internally, all species (including Petauroides) have a large cecum for fermenting their leaf-based diet, and their cheek-teeth are formed in the shape of cutting edges, scissorlike, to both cut and grind xerophytic leaves (e.g., Eucalyptus, which at least some species can detoxify).
Distribution
Pseudocheirids obviously already were part of the Australian fauna in times when the Australian continent still rested in wetter climatic zones. Species existing then, similar to other families, were larger than today's representatives, reaching up to 33 lb (15 kg). With increasing aridification of the Australian continent, pseudocheirids withdrew to the still wetter areas, and today are restricted to coastal, or coast-near areas in the east, northeast, southwest and northwest of the continent, as well as Tasmania. New Guinea seems to have been invaded rather late, and the species there are mostly restricted to mountainous, i.e., central areas.
Habitat
Nearly all of the New Guinean species, except for two rather poorly known and obviously rare species (Pseudochirulus canescens, Pseudocheirus caroli), inhabit mountain forests, where they are rather abundant. All of them prefer primary forests except Pseudocheirus forbesi, who seem to be more adapted to secondary, i.e. disturbed forest areas. There are up to four sympatric species in certain New Guinean places, and in those communities there are clear niche-separations in size, ranging from 5.3 to 70.5 oz (150 to 2,000 g) and nesting habits (from tree-hollows to dreys to sleeping exposed on branches). In Australia, one species (Petropseudes dahli) is semi-terrestrial, preferring rocky areas in Northern Australia, two species are found in sclerophyll forests (P. volans and Pseudocheirus peregrinus), and the rest are living in higher altitude rainforests of the Atherton Tableland. Contrary to New Guinea, these sympatric species (which also are in part sympatric to some phalangerid species) are all in the same size class, namely, in the 31.7–42.3 oz (900–1,200 g) range, and all except one, rest in tree-hollows. Supposedly, niche-differentiation must be along some other axes, one of them possibly activity—each species has characteristic times of emerging and returning from and to nests, the aspect of the nesting-tree, or size of the hollows. Among the sclereophyll forest-dwellers, Pseudocheirus peregrinus has been able to adapt to suburban habitats, feeding on rosebuds and rose leaves in front- and backyards, and daynesting under roofs.
Behavior
Pseudocheirids are among the most diverse of all possums in term of social organization. The rock ringtail (Petropseudes dahli) seems to live in long-term pairs with overlapping young, as they have been observed as pairs with a young-at-heel, and another smaller one riding on back. Lemuroid ringtails are long-term monogamous, perhaps with a potential to an expansion similar to P. dahli, P. peregrinus is reported as either pair- or family-living, with paternal care such as carrying grooming and defending young. Sleeping groups of adults of varying sexual composition have also been recorded. Most of the rainforest species and P. volans are solitary both while foraging and resting.
Deposit of feces on specific sites has been found in P. dahli, and a sternal gland is used by sternal rubbing in several species of Pseudocheirus. Acoustic communication seems to be of medium importance, with distress calls uttered by young in trouble, soft contact calls by family members of P. peregrinus, loud contact calls, possibly for spacing, as a "dusk" chorus of P. forbesi, and vocal recall of young from dangerous situations in P. peregrinus. There is no evidence of territorial defense in any species, even the solitary ones, except a certain spatial distribution pattern of P. volans that is more evenly distributed than statistically expected from randomness. This suggests at least active avoidance, or perhaps some sort of defense. All species are mostly nocturnual. Pseudochirops archeri sometimes can be seen active during the day.
Feeding ecology and diet
Petauroides volans is a highly specialized folivore, who feeds about 90% of its diet on eucalyptus leaves. It relies on high nutrient species or growth stages, and seems to be able to actively select these high-quality leaves based on tree species and leaf age. All the remaining species, so-called ringtails, also are folivores, and at least some species, such as Pseudocheirus peregrinus, are also capable of eating high amounts of eucalyptus leaves. However, they mostly do not rely so heavily on eucalypts alone, eating buds, flowers and fruits of other plants, in the understory of eucalypt forests as well. All leaf-eating pseudocheirids are hindgut-fermenters, which means that in their large colon and cecum, a specialized community of bacteria and other microorganisms is kept to digest cellulose (plant cell walls cannot be digested by any animal). They are all capable, in their hindgut, to separate the contents into large particles, which are defecated rather quickly, and small particles, solubles and bacteria themselves. This mechanism serves to retain the more digestible parts and nitrogen-carrying bacteria. Ringtail possums also are caecotrophic; the colon contents are defecated separately, and ingested again to gain proteins and amino acids by foregut digestion. Eucalypt-feeding ringtails often show strong preferences for certain trees, and dislike for other trees of the same species. Subsequent chemical analysis revealed a higher proportion of toxic or unpalatable substances in the rejected individuals. They are, however, when not given a choice, capable of detoxifying the toxic plant secondary metabolites, though at a cost of higher energy and nitrogen requirements.
Reproductive biology
Mating systems of pseudocheirids, as already suggested by their diverse social organization, are rather variable. Several species are long-term monogamous, which may also include paternal care. Others, the solitary ones included, are polygamous, with evidence for shifts from monogamy to polygyny between years for the greater glider, depending on the food supply. Breeding in Petauroides is seasonal, one young per year being born in autumn to winter. The young stays in the pouch for 90–120 days, and is carried on the mother's back for another 90 days. Young become independent around 10 months of age, and sexually mature during their second year. The tropical ringtails, particularly those from New Guinea, seem to have no reproductive season. Consort relationships, an accompanying by a male for an estrous female for a few days, have been described for some species, nothing else is known about mating systems of the solitary ones. Number of young per litter is one or two, depending on the species, and it seems that, as far as known, the age of 120 days for leaving the pouch characterizes them all. Weaning occurs, again known only for some species at 150–160 days (Pseudochirulus herbertensis) to 180 days (Pseudocheirus peregrinus). Females, at least in P. peregrinus, are capable of producing two litters per year. Longevity in the wild is approximately four to five years.
Conservation status
Several species of pseudocheirids are either widespread, and ecologically adaptable (e.g., P. peregrinus), or quite abundant in their current habitat, which is not under immediate threat. Others, however, are vulnerable due to a restricted area of distribution (e.g., some of New Guinean species, or the rock ringtail). Among the New Guinean species, several are unknown in status and biology. None of the potentially vulnerable species is currently protected under Indonesian or Papua law, and the system of proposed or established natural reserves may be inadequate to protect them, also because the reserves have been proposed without considering the needs of local people or animals themselves. Petauroides volans is considered vulnerable due to its dependence on old, hollow trees for nesting, and due to its patchy distribution even in prime habitat. Over 50% of the forest, even in areas where it is common, is never used, and over 60% of individuals used 9% of the available forest in one study. Logging of such areas has tremendous negative effects.
A different kind of threat is expected to arise over the next few years or decades. Due to global warming and increasing carbon dioxide (CO2) levels, eucalypts are expected to increase the level of toxins and antinutrients in their leaves (because these secondary metabolites are a common way of storing chemical waste in plants). It has been calculated that, given the current amount of increasing CO2 levels, within the next 50 years most of Australian's eucalypt forests will be uninhabitable for leaf-eating species, such as greater gliders.
Significance to humans
Some of the larger New Guinean species are hunted for meat.
Species accounts
Lemuroid ringtailGreater glider
Green ringtail
Rock ringtail
Common ringtail
Lowland ringtail
Herbert River ringtail
Pygmy ringtail
Resources
Books:Cork, Stephen J., and William J. Foley. "Digestive and
Metabolic Adaptations of Arboreal Marsupials for Dealing with Plant Antinutrients and Toxins." In Marsupial Biology—Recent Research, New Perspectives, edited by Norman Saunders and Lyn Hinds. Sydney: UNSW Press, 1997.
Flannery, Tim F. Possums of the World. Chatswood, Australia: Geo Productions, 1995.
Goldingay, Ross L. "Gliding Mammals of the World. Diversity and Ecological Requirements." In Biology of Gliding Mammals, edited by Ross L. Goldingay and John S. Scheibe. Fürth: Filander Verlag, 2000.
Kennedy, Michael, ed. Australasian Marsupials and Monotremes—An Action Plan for their Conservation. Gland, Switzerland: IUCN Publication Department, 1992.
Strahan, Ron, ed. The Australian Museum Complete Book of Australian Mammals. Sydney: Australian Mammals; Sydney: Australian Museum, 1995.
Winter, John W. "Australasian Possums and Madagascan Lemurs." In Comparison of Marsupial and Placental Behaviour, edited by David B. Croft and Udo Ganslosser. Fürth, Germany: Filander Verlag, 1996.
[Article by: Udo Gansloßer, PhD]
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