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The family Dasypodidae, the armadillos, includes 21 species placed in 8 genera, all found only in the New World (the 21st armadillo species to be recognized, Dasypus yepesi, was described only in 1995 from the Gran Chaco of Paraguay and northern Argentina). Armadillos occur from the southern United States to the Straits of Magellan. Only the Nine-banded Armadillo (D. novemcinctus) reaches as far north as the United States.
The dorsal surface of an armadillo's body is covered with bony plates that protect the head, back, and sides and sometimes the legs and tail. Around the center of the body this armor is arranged into bands of plates separated by soft skin, allowing the animal to bend its body (the number of bands is often a useful character in distinguishing armadillo species). The back is smoothly rounded and the legs are short and powerful, with strong claws on the toes. There are three to five toes on the forefeet and five on the hindfeet. The belly is soft and naked. Most species have little or no hair, but one montane species has dense hair covering the armor.
Armadillos are generally termite and ant specialists (although other animal and even plant food is consumed as well). All species apparently sleep and raise their young in burrows they dig themselves, each species building a burrow with a characteristic size and shape. An armadillo burrow can be recognized by its smooth dome-shaped roof. The litter size is 1 to 12 young.
Head and body length among armadillo species ranges from around 125 to 1000 mm and tail length from 25 to 500 mm. The Giant Armadillo (Priodontes maximus) may weigh as much as 60 kg, whereas the little known Pink Fairy Armadillo (Chlamyphorus truncatus) and Chacoan fairy armadillo (Calyptophractus retusus), which are both thoroughly adapted to a subterranean lifestyle, weigh only around 100 g (Delsuc et al. 2012 and references therein). Armadillos have small ears. The snout, which encloses a long protrusible tongue, varies considerably in length and all species have very reduced peglike dentition, with no incisors or canines.
Armadillos generally inhabit open areas such as savannahs and pampas, but they also occur in forests (four genera and eight species are found in lowland rainforest). They travel singly, in pairs, or occasionally in small groups and may be diurnal or nocturnal. Armadillos can run surprisingly rapidly. Armadillos in a few species may roll themselves into a ball when threatened.
(Emmons 1990; Nowak 1991)
The Nine-banded Armadillo has been the focus of much research on polyembryony. Polyembryony, the production of two or more embryos from a single zygote (fertilized egg), occurs sporadically in diverse animal taxa (including humans). Among the vertebrates, only armadillos of the genus Dasypus are known to utilize polyembrony as their standard reproductive mode. Each litter is typically a set of four identical quadruplets derived from a single fertilized egg. (Prodohl et al. 1996; Loughry 1998)
In the 1970s it was discovered that Nine-banded Armadillos could contract leprosy and since then armadillos have been the primary animal model in leprosy research. Genetic and other studies have revealed that, although leprosy was absent from the New World prior to European colonization, leprosy now occurs naturally in New World armadillo populations (with a prevalence exceeding 20% in some populations). Infected armadillos have been reported in Alabama, Arkansas, Louisiana, Mississippi, Texas, and Mexico. Although the United States sees only around 150 new cases of human leprosy each year, and two thirds of these are in people who have traveled to regions with endemic leprosy, around 50 cases a year appear to have been contracted within the U.S., often in Texas or Louisiana. Truman et al. (2011) found that a high percentage of unrelated leprosy cases in the southern United States involve infection with the same unique strain of the responsible bacterium, Mycobacterium leprae, that occurs naturally among wild armadillos in the region. These armadillos thus appear to represent a large natural reservoir for M. leprae. However, high prevalence rates among armadillos have been observed in only parts of the southern United States, mainly in the western Gulf Coast states. (Truman et al. 2011 and references therein)
Nine-banded Armadillos apparently crossed the Rio Grande into southeastern Texas some time in the 1820s. In contrast, the eastern population apparently originated from a separate introduction of armadillos into south-central Florida in the 1920s, which subsequently expanded and has only relatively recently merged with the main U.S. population. The extent to which leprosy will become established in eastern armadillo populations remains to be seen. In humans, susceptibility to leprosy appears to depend on multiple genes and the majority of people appear to be naturally immune to M. leprae infection, somewhat moderating the risk to the general human population, although extensive contact with or consumption of armadillos is not recommended. (Loughry et al. 2009 and references therein; Truman et al. 2011 and references therein)