Mammals, Biodiversity of Guinea and with no known fossil record, both species have long stiff hairs on either side of their tails, from which they derive their name The gliders, which weigh a mere 10–15 g, have membranes between the elbows and knees, further aiding gliding flight The membrane is lacking in the possum, which weighs up to 50 g Gliding as a strategy appears to have evolved twice in the diprodonts Six species of lesser glider, three species of triok, and the striped and Leadbetter’s possum make up the family Petauridae Found from Tasmania to New Guinea, the petaurids resemble small squirrels Weighing from 100 to 700 g, they have long bushy tails and stripes down their backs The striped possum has black and white dorsoventral stripes along the back, resembling a North American skunk in coloration The six gliders bear a remarkable resemblance to flying squirrels of the genus Glaucomys in the Rodentia order A membrane that stretches between their wrists and ankles provides an almost rectangular, kitelike gliding surface that these animals use to move from tree to tree Whereas the striped possum is an insectivore, all other members of the family specialize on eating plant exudate (sap and gum) as well as insects The sugar glider (Petaurus breviceps) is particularly specialized, concentrating its efforts on the exudate from a single species of Eucalyptus Resembling fossorial rodents, the three extant species of wombat have short, muscular limbs, stocky bodies, and broad long claws They are large animals, weighing up to 40 kg Prodigious diggers, they live in complex burrow systems, which caused them to be called marsupial badgers on their first discovery Unique among marsupials, their teeth are evergrowing like those of rodents and lagomorphs Wombats are herbivores, concentrating their diet on tussock grasses Wombats are found only in southern Australia and Tasmania, with the northern hairy-nosed wombat (Lasiorhinus krefftii) found in one isolated population of 70 individuals living on km2 in central Queensland Wombats have a long fossil history in Australia, with two much larger species occurring throughout the Pleistocene and going extinct about 10,000 years ago, coincident with the arrival of humans and dogs The best known family of diprodonts, and probably the most widely recognized family of marsupials, are the 11 genera and 65 recent species of macropods, the kangaroos and wallabies Ranging in size from to 90 kg, all species share the same basic body plan Forelimbs are reduced and have five toes, all bearing small claws The hind limbs are elongated, and, as in the bandicoots, on the hind leg all but the fourth digit has been reduced or lost The large hind foot allows macropods to take a bipedal stance The limbs are highly adapted for ricochetal or hopping locomotion that, because of the limb structure, is highly energy efficient Each time the kangaroo bounces down, the large elastic tendons in the foot are stretched taut like a rubber band, storing energy from the previous bounce As the foot is released, the tendons snap back and push the foot off the ground, throwing the kangaroo into the air On landing, the tendons are stretched taut again, completing the cycle In addition to the remarkable limb adaptations, macropods have a digestive system remarkably similar to that of the eutherian ruminant herbivores they ecologically replace Both groups have evolved segmented stomachs, with a true 689 chambered stomach in the ruminants and a divided, three-part stomach in macropods This segmentation allows for the acquisition of foregut fermentation, in which symbiotic bacteria digest the tough outer cell walls of the plant materials that the animal eats, thus releasing nutrients from within the cell, providing a digestible form of cellulose (which is broken down by the bacteria), and nutrients from the bacteria themselves as they are absorbed when they pass through the gut Macropods have a wide geographic range and habits Whereas macropods are usually thought of as long-distance, open-plains grazers, in New Guinea tree kangaroos in the genus Dendrolagus have adopted an arboreal habit Although these animals still spend much of their time on the ground foraging for fallen fruits, they are agile climbers and use their large hind feet to propel them from tree to tree Many of the smaller wallabies are also habitat specialists, such as the 16 species of rock wallabies (Petrogale sp.) Placentals Placentals dominate both the fossil and recent history of the Mammalia With three times number of orders of marsupials (21 vs 7), placentals have shown remarkable diversification at all lower levels Recent species are grouped into 21 orders with 130 families, 1134 genera, and approximately 4480 species (Table 2) As in the marsupials, some lineages contain disproportionately more families, genera, and species than others With a fossil record stretching back into the Cretaceous, eutherian mammals have a long evolutionary history derived from marsupials and monotremes Found on all continents, the placentals show remarkable niche diversification, occupying a wide variety of terrestrial, aerial, and aquatic habitats and subsisting on diets ranging from the true omnivorous habits required to live on the varied detritus of human populations to a single group of grasses (pandas and bamboo) or termites Pilosa The superorder Xenarthra, which includes orders Pilosa (anteaters and sloths) and Cingulata (armadillos), encompasses a group found in recent times only in the New World Thought to have occurred in Europe, the fossil record is, at best, fragmentary To appreciate the diversity of the Xenarthra, take a journey back into Miocene South America The modern-day sloths of Pilosa have quite the ancestral past; giant sloths, commonly called ground sloths or sloth bears, were as huge as their name would indicate Whereas Tertiary radiations included a variety of species exploiting numerous habitats and niches, the members of the extant families of Pilosa are relatively or highly specialized: all four species of anteaters (Mymecophagidae and Cyclopedidae) are obligate ant and termite eaters, using their long, sticky tongues to collect their food The sloths (six species in two families) have acquired an odd but apparently effective strategy, shifting along tree branches upside down, their spines hanging in a catenary curve Sloths are the only green mammals; however, their color is not intrinsic to their fur but is derived from algae and cyanobacteria that grow in grooves in their hair Sloths come down to the ground only to defecate