About Chaetophractus villosus (Desmarest, 1804)
Chaetophractus villosus, commonly known as the big hairy armadillo, is the most abundant armadillo species in Argentina. Its head and body are covered in protective bony plates, with the head plate being the most prominent. Flexible bands that encircle the torso along its back give flexibility to its otherwise stiff armor. The underside of the big hairy armadillo is densely covered in hair, which is how it earned its common name. Long, coarse hairs also grow out from the bony plates, making this species much hairier than other related armadillo species. When mature, the average body length of an individual is 26 to 34 cm (10 to 13 in), with extreme cases ranging from 22 to 40 cm (8.7 to 15.7 in). Mature individuals average 2 kg (4.4 lb) in weight, with a total weight range of 1 to 3 kg (2.2 to 6.6 lb). The tail measures 9 to 17 cm (3.5 to 6.7 in) long. Powerful front claws are used both for foraging and escaping predators. This armadillo has specially evolved nasal membranes that let it obtain oxygen from surrounding soil particles without inhaling soil itself. The genus Chaetophractus contains two or three species: C. vellerosus (the screaming hairy armadillo), C. nationi (the Andean hairy armadillo, which may actually be a population of C. vellerosus), and C. villosus. All species in this genus are recognized by the large amount of hair covering their bodies, especially their undersides. Their skulls follow the same general pattern as other dasypodids, but females have longer bones in the rostrocaudal plane, which is a key characteristic showing the sexual dimorphism of these species. Little is known about the cranial morphology of these Chaetophractus species, particularly when it comes to bone descriptions. More research is ongoing to better describe these species and the skeletal differences between them; for now, body size, habitat, and behaviors are the most reliable ways to tell the species apart. The natural home range of C. villosus covers a continuous area across large parts of Argentina, Bolivia, and Paraguay. In Argentina, its natural range extends beyond the Pampas, reaching as far south as Santa Cruz Province in southern Patagonia. The species was introduced to Tierra del Fuego Island in 1982, spreading from a property northeast of Río Grande. The introduced individuals originally came from Buenos Aires Province, and have adapted well even though Río Grande has a mean annual temperature 2 to 3 °C lower than Río Gallegos, which sits near the southern limit of C. villosus' natural distribution. C. villosus is a member of the family Chlamyphoridae, and its members, including C. villosus, have evolved distinct specialized traits to support survival. The most well-known of these are the bony plates covering the head and back, which provide a substantial level of protection from natural predators. This species also has a remarkable respiratory adaptation for when its nostrils are fully covered in soil: it can maintain sufficient respiration using a mechanism that lets it use air trapped between soil particles, without inhaling the soil particles themselves. Along with its powerful digging claws and high surface-area-to-mass ratio, this adaptation supports its fossorial, or subterranean, lifestyle. Even with the added challenges of burrowing, this armadillo maintains similar surface-area-to-mass ratios as non-fossorial species. This suggests it adapted to a burrowing lifestyle to avoid extreme temperatures and predators, rather than to support foraging. Little is known about hemostasis in this species. Platelet counts are similar between sexes, and remain similar even when individuals are held in captivity. Counts are comparable to most other mammals, and the species reacts the same way to proven hemostatic agonists. More research in this area could lead to new biomedical advances, but little additional information is currently available. Studies of C. villosus penis muscles have found the species' very long penis has variable traits and behaviors. During waking hours, the penis stays hidden inside a skin receptacle, only projecting outward in a rostral direction when it becomes erect. During the slow wave sleep phase, the penis makes complex movements while protruding. In this sleep phase, the penis is not erect, but remains outside of its receptacle. During paradoxical sleep, no erections occur, and the penile muscles share the same characteristics as the rest of the body's muscles.
