EDENTATE

Nine-banded armadillo (Dasypus novemcinctus). a member of the mammalian order Edentata, which includes all the armadillos (see photograph), true anteaters, and tree sloths. All these animals are members of the suborder Xenarthra, which also contains the extinct ground sloths and glyptodonts (turtle armadillos). The other suborder, Palaeanodonta, consists of two families of extinct armadillo-like forms. The edentates have been restricted to the Western Hemisphere during their entire evolutionary history; 31 living species are known, most of them in South America. Although the name Edentata means without teeth, only the true anteaters (Myrmecophagidae) are totally toothless. Armadillos (Dasypodidae) and tree sloths (Bradypodidae) possess peglike teeth that lack enamel; some armadillos have as many as 100 of these teeth. The tree sloths have continuously growing teeth covered with a hard cement that protects them against excessive wear from their highly abrasive herbivorous diet. Tree sloths have a shaggy yellow-to-brown fur, which in the wild has a greenish tint from the algae that inhabit it. Their long limbs and long, curved claws are adapted to support the animals while hanging upside down from branches; on the ground they are virtually helpless, but they are excellent swimmers. Anteaters range in size from the 37-centimetre (15-inch), 325-gram (12-ounce) silky anteater (Cyclopes didactylus) to the 2-metre (6-foot), 25-kilogram (55-pound) giant anteater (Myrmecophaga tridactyla). The two arboreal anteaters, the silky and the tamandua (Tamandua tetradactyla), have prehensile tails. All three anteaters have elongated heads and sharp, sturdy claws. Enlarged salivary glands secrete a sticky saliva that coats the long, extrusible tongue. Silky anteaters are usually a soft golden colour; tamanduas are tan to brown, with black markings on the chest. The giant anteater is gray with a white-edged black stripe along each side. The shaggy hair is especially long and straight on the large, plumed tail. Armadillos range in size from the tiny pink fairy armadillo (Chlamyphorus truncatus), which is only 16 cm long and weighs about 100 g, to the giant armadillo (Priodontes giganteus), a 25-kg animal that can reach 1.5 m in length. The major characteristic of armadillos is their dorsal carapace, a shield composed of several bony plates separated by movable bands. Contrary to popular belief, most species cannot roll up into a completely shielded ball; only the three-plated armadillo (Tolypeutes tricinctus) can do this. Some species, such as the nine-banded armadillo (Dasypus novemcinctus), can close up quite well, but others merely lower themselves to the ground and use the carapace as a protective shield. The tree sloths are the only living herbivorous edentates; the two-toed sloth (Choloepus didactylus) eats fruits, stems, and leaves from a variety of plants, but the three-toed sloth (Bradypus tridactylus) has a diet restricted to the leaves of the cecropia tree. Tree sloths are found from southeastern Honduras to northern Brazil. They are solitary creatures and depend mostly on their camouflaged coloration and lack of motion for protection from predators. A cornered sloth, however, can bite savagely and use its long claws to good advantage. Anteaters find their prey by the sense of smell. The long, sharp claws are used to rip apart ant nests and termite mounds, and the sticky tongue is highly effective in lapping up the insects. All three species can use their daggerlike foreclaws for self-defense. Myrmecophagids are found from Argentina northward into Mexico. Armadillos are the most omnivorous members of the order, eating small reptiles and amphibians, insects and other invertebrates, carrion, and some vegetation. They have an acute sense of smell, and some can locate insects that are hidden as deep as 12 cm underground. In addition to rolling up for protection, many armadillos dive into their burrows when threatened; some species can wedge themselves firmly into the burrow, flexing the bony carapace and digging in with the claws. Armadillos are exceptionally good diggers and occasionally will try to burrow speedily into the ground when in danger. The nine-banded armadillo is the only living edentate found north of Mexico; it ranges north into Kansas, and introduced populations have established strong footholds in Florida and other southeastern states. Other armadillo species are found throughout most Central and South American habitats as far south as Argentina. Edentate reproduction is varied. The shortest gestation period, 65 days, occurs in the hairy armadillo (Chaetophractus villosus) and the longest, 263 days, in the two-toed sloth. Dasypus exhibits both of the distinctive reproductive phenomena found in various representatives of this order: polyembryony, with 212 identical embryos developing from one fertilized ovum (Dasypus almost always bears quadruplets), and delayed implantation, with the early embryo floating freely in the uterus for as long as several months before implanting in the uterine wall and continuing its development. Dasypus breeds between June and September, but implantation does not occur until November, and the young are always born in early spring. Young armadillos have a leathery carapace that hardens with age, and they are able to walk shortly after birth. Young tree sloths are born with their eyes and ears open. They cling to the mother and suckle until five months of age and are on their own at nine months. Young anteaters also ride on the mother. The North American paleanodont edentates lived from the late Paleocene into the Oligocene (about 57.8 million to 36.6 million years ago). In the Southern Hemisphere the first Xenarthra also appeared during the Paleocene. This suborder underwent a large adaptive radiation. Several families of sloths appeared and died out, as did two lines of armadillo-like creatures, including the glyptodonts (Glyptodontidae). Two of the largest edentates lived in South America during the Pleistocene Era (some 500,000 years ago). These were the ground sloth Megatherium americanum, which was 6 m long, and the glyptodont Doedicurus clavicaudatus, which reached 4 m long and stood 1.5 m high. Nine-banded armadillo (Dasypus novemcinctus). any member of the mammalian order Edentata, which includes 31 living species distributed among the armadillos (see photograph), true anteaters, and tree sloths, as well as eight extinct families of ground sloths and armadillo-like animals. The living families and six of the extinct families constitute the suborder Xenarthra. A second suborder, Palaeanodonta, consists of two extinct families. The entire evolutionary history of the edentates is restricted to the Western Hemisphere, and the majority of the living species occur today in South America. Additional reading The following works, although broad in scope, are particularly rich in information on the edentates: J.C. Barlow, Edentates and Pholidotes, in S. Anderson and J.K. Jones, Jr. (eds.), Recent Mammals of the World (1967), a discussion of the taxonomy of this order and its families; J. Dorst, South America and Central America: A Natural History (1967), many fine photographs of edentates; E.R. Hall and K.R. Kelson, The Mammals of North America, 2nd ed., 2 vol. (1981), descriptions and distributional information on North and Central American members of this order; R. Hoffsteter, Xenarthra, and R. Saban, Palaeanodonta, in J. Piveteau (ed.), L'Origine des Mammifres evolution, 2 vol., pt. 6 of Trait de palontologie (1958), detailed accounts of early edentates; and E.P. Walker, Mammals of the World, 2nd ed., vol. 1 (1968), an account of the natural history and distribution of every genus in the order. Jon Charles Barlow