Class Mammalia Order Diprotodontia Family Potoroidae
Small- to medium-sized marsupials that generally hop like kangaroos; they have an elongated tail; females have a pouch with four teats and usually have one young
Number of genera, species
4 genera; 8 species
Extinct: 2 species; Critically Endangered: 1 species; Endangered: 2 species; Vulnerable: 1 species; Lower Risk/Conservation Dependent: 1 species; Lower Risk/Near Threatened: 1 species
Mainly coastal Australia; absent from northern coast
Mainly coastal Australia; absent from northern coast
Rat-kangaroos have been traditionally classified as a subfamily of their nearest relatives, the kangaroo and wallaby family (Macropodidae). However, most taxonomists now accept the separation of two groups into families with the Potoroidae being separated from the Macropodidae on the basis of their urogenital anatomy. The two groups are often associated into a single superfamily, the Macropodoidea. These families have been separate for at least 50 million years. Within the Potoroidae there is one group: the Po-toroinae, which contains the extant genera of Potorous, Bettongia, and Aepyprymnus. Within the Potoroinae, Bettongia and Aepyprymnus are more closely related to each other than to Potorous.
These animals are all smaller than a medium-sized cat. The upper fur is variously gray-brown with the belly usually much lighter. The ears are short and rounded. The face is short though the nasal region is somewhat elongated. The fore-limbs are considerably shorter than the hind limbs, which are
elongated in a similar manner to that of the larger kangaroos. The tail is usually furred, and in the brush-tailed bettong (B. penicillata), there is a crest on the distal dorsal surface. In P. tridactlus and B. gaimardi, the tail tip is white; the significance of this is not known. Some bettongs have a prehensile tail that is used to transport nest material (leaves and grass) for nest building. There are three pairs of upper incisors but only one pair of lower, and young potoroids have two premolars, though near maturity these are replaced by a single sectorial molar. The molar teeth erupt gradually and the fourth molar may not erupt for three to four years. There is a lack of sexual dimorphism in the bettongs.
The family is confined to coastal Australia in mainly the southern half, though B. tropica is found in northeastern Queensland. Bettongia gaimardi is found only on the island of Tasmania where it is still locally common. Potorous tridactlus is distributed from southern Queensland through New South Wales into most of Victoria as well as Tasmania. Potorous
Bettongs have prehensile tails with which they may carry nest materials. (Illustration by Jarrod Erdody)
longipes is only found in a very restricted area of Victoria while P. gilberti occurs only in Two People's Bay Nature Reserve, Western Australia. Bettongia lesueur is found on a few islands off the west coast of Western Australia and B. penicillata is found in pockets in southwest Western Australia and has been translocated to a number of islands off South Australia. Bet-tongia lesueur is restricted to only three islands of the west coast of Western Australia. Aepyprymnus is found only in New South Wales and Queensland.
Most potoroids live in forest or woodland areas dominated by eucalyptus species. However, in the recent past, B. lesueur and B. pencillata lived over much of arid Australia. Bettongia lesueur, the burrowing bettong, lives in warrens that can be in sandy dunes. Potoroos tend to live in wetter forest areas than the bettongs, which prefer the more open forest that is better suited to their high hopping gait.
Not a great deal of behavioral studies have been carried out on this nocturnal group. They are generally solitary, though some bettong males and females may cohabitate for short periods after mating. Males regularly check up on females living in their home range by inspecting their pouch and/or urogenital regions. This allows males to be aware of the reproductive status of the female and the imminence of estrus. Males can be aggressive towards other males, which generally takes the form of lashing out with their hind feet. Animals that are anxious often display a sinuous movement of the tail. Female bettongs not in estrous can also be aggressive towards unwelcome males, lashing out with their hind feet while lying on their side. Mating takes place usually only on the night of estrus and involves rear-entry while the male holds the female with his forelimbs around her flank. He may also hold on to her neck with his teeth. Intromission is usually of a few seconds duration but may occur several times in a night. This group makes few vocalizations, though females make a clucking-like sound to attract their young to the pouch. Anxious animals make a vocalization with an explosive expelling of air.
The bettongs and potoroos are mainly fungivores, eating a large proportion of the fruiting bodies of underground (hy-pogeous) fungi. In order to accomplish this, it is necessary that they have a well-developed sense of olfaction; a large proportion of their cortex is devoted to this. Animals dig with their forefeet to access their diet. The well-developed fore-stomach of potoroids allows them to have sufficient time to digest the fungi and the gut flora/fauna assist in providing essential amino acids that may be absent from the diet. Animals can exist almost exclusively on fungi, which provide a nourishing diet high in both protein and lipid. The fungi grow on the roots of eucalyptus and other native trees and their spores are activated during passage through the bettong's gut, thereby allowing germination at the site of defecation.
Rat-kangaroos are probably polygynous and have a reproductive biology quite similar to that of their larger relatives, the kangaroos and wallabies. After a short gestation, usually about three weeks, the neonate crawls unaided to the pouch where it attaches to one of the four teats. On that night the mother comes into estrous, termed a postpartum estrus, and mates again. The resultant fertilized egg develops only to the blastocyst stage of about 100 cells before becoming dormant, termed embryonic diapause. It remains in the uterus until it is reactivated near the end of pouch development of the previous young. Then, usually on the same night that the large offspring finally vacates the pouch, the new offspring is born. Again, the mother will come into postpartum estrus and mate again. Thus, the rat-kangaroo can have three different generations at the same time: one young out of the pouch still suckling from her teat, one newborn young in the pouch, and one dormant embryonic stage in her uterus. All species give birth to one young at a time. The pouch contracts after the large offspring leaves the pouch, preventing its return and thereby protecting the newborn smaller young. The milk suckled by the young in the pouch is constantly changing its composition from a dilute milk low in protein and lipid but high in carbohydrate to one that becomes more concentrated and high in lipid and low in carbohydrate.
Bettongia tropica, Gilbert's potoroo, and the long-footed potoroo are listed as Endangered in the Environment Pro-
tection and Biodiversity Conservation Act 1999 of the Commonwealth of Australia. Bettongia lesueur and the long-nosed potoroo in southeast Australia are listed as Vulnerable. The IUCN lists Gilbert's potoroo as Critically Endangered, the long-footed potoroo and northern bettong as Endangered, boodie as Vulnerable, brush-tailed bettong as Lower Risk/ Conservation Dependent, and the Tasmanian bettong as Lower Risk/Near Threatened.
Significance to humans
Although rat-kangaroos are attractive animals, they have little significance in either a cultural or agricultural context.
1. Northern bettong (Bettongia tropica); 2. Rufous bettong (Aepyprymnus rufescens); 3. Long-footed potoroo (Potorous longipes); 4. Boodie (Bet-tongia lesueur); 5. Long-nosed potoroo (Potorous tridactylus); 6. Gilbert's potoroo (Potorous gilbertii); 7. Tasmanian bettong (Bettongia gaimardi); 8. Brush-tailed bettong (Bettongia penicillata). (Illustration by Bruce Worden)
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