| Armadillo | |
|---|---|
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| From top to bottom:nine-banded armadillo (Dasypus novemcinctus),pink fairy armadillo (Chlamyphorus truncatus) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Superorder: | Xenarthra |
| Order: | Cingulata |
| Families | |
Armadillos (Spanish for 'little armored ones') areplacental mammals in the orderCingulata. They form part of the superorderXenarthra, along with theanteaters andsloths. Twenty-one extantspecies of armadillo have been described, some of which are distinguished by the number of bands on their armor. All species are native to theAmericas, where they inhabit a variety of environments.
Living armadillos are characterized by a leatheryarmor shell and long, sharp claws for digging. They have short legs, but can move quite quickly. The average length of an armadillo is about 75 cm (30 in), including its tail. Thegiant armadillo grows up to 150 cm (59 in) and weighs up to 54 kg (119 lb), while thepink fairy armadillo has a length of only 13–15 cm (5–6 in). When threatened by a predator,Tolypeutes species frequently roll up into a ball; they are the only species of armadillo capable of this.
Recent genetic research has shown that themegafaunalglyptodonts (up to 1.5 metres (4.9 ft) tall with maximum body masses of around 2 tonnes), which became extinct around 12,000 years ago are true armadillos more closely related to all other living armadillos than toDasypus (the long-nosed or naked-tailed armadillos). Armadillos are currently classified into two families,Dasypodidae, withDasypus as the only living genus, andChlamyphoridae, which contains all other living armadillos as well as the glyptodonts.[1]
The wordarmadillo means'little armored one' in Spanish;[2][3] it is derived fromarmadura'armor', with the diminutive suffix-illo attached. TheAztecs called themāyōtōchtli[aːjoːˈtoːt͡ʃt͡ɬi],Nahuatl for'turtle-rabbit':āyōtl[ˈaːjoːt͡ɬ]'turtle' andtōchtli[ˈtoːt͡ʃt͡ɬi]'rabbit'.[4] ThePortuguese word for'armadillo' istatu which is derived from theTupi language[5]ta''bark, armor' andtu'dense';[6] and used in Argentina, Bolivia, Brazil, Paraguay and Uruguay; similar names are also found in other, especially European, languages.
Other various vernacular names given are:
FamilyDasypodidae
FamilyChlamyphoridae
† indicates extinct taxon
The earliest armadillos appeared in South America during the earlyEocene epoch, around 52–55 million years ago.[9] The modern groups of armadillos are thought to have diverged from each other in the Eocene.[10][11] Recent morphological[12] and genetic[1][11] evidence indicates that the largeglyptodonts andpampatheres, both of which went extinct as part of theend-Pleistocene extinction event around 12,000 years ago, are nested within the diversity of living armadillos. Below is a recent simplified phylogeny of theCingulata based on genetics and analysis of the inner ear.[12] The dagger symbol, "†", denotes extinct groups.
Like all of the Xenarthra lineages, armadillos originated inSouth America. Due to the continent's former isolation, they were confined there for most of theCenozoic. The recent formation of theIsthmus of Panama allowed a few members of the family to migrate northward into southernNorth America by the earlyPleistocene, as part of theGreat American Interchange.[13] (Some of their much largercingulate relatives, thepampatheres and chlamyphoridglyptodonts, made the same journey.)[13]
Today, all extant armadillo species are still present in South America. They are particularly diverse inParaguay (where 11 species exist) and surrounding areas. Many species are endangered. Some, including four species ofDasypus, are widely distributed over the Americas, whereas others, such asYepes's mulita, are restricted to small ranges. Two species, thenorthern naked-tailed armadillo andnine-banded armadillo, are found in Central America; the latter has also reached the United States, primarily in the south-central states (notably Texas), but with a range that extends as far east asNorth Carolina andFlorida, and as far north as southernNebraska and southernIndiana.[14] Their range has consistently expanded in North America over the last century due to a lack of natural predators. Armadillos are increasingly documented in southernIllinois and are tracking northwards due toclimate change.[15]
The smallest species of armadillo, thepink fairy armadillo, weighs around 85 g (3.0 oz) and is 13–15 cm (5.1–5.9 in) in total length. The largest species, thegiant armadillo, can weigh up to 54 kg (119 lb), and can be 150 cm (59 in) long.[16]
In common with other xenarthrans, armadillos, in general, have lowbody temperatures of 33–36 °C (91–97 °F) and lowbasal metabolic rates (40–60% of that expected in placental mammals of their mass). This is particularly true of types that specialize in using termites as their primary food source (for example,Priodontes andTolypeutes).[17]
The armor is formed byplates ofdermal bone covered in relatively small overlapping epidermal scales called "scutes" which are composed of keratin.[18] The scutes are held together by collagen fibres that can contract to curve following the armadillo's body shape.[19]: 713–715 The skin of an armadillo can glow under ultraviolet light.[20]Most species have rigid shields over the shoulders and hips, with a number of bands separated by flexible skin covering the back and flanks. Additional armor covers the top of the head, the upper parts of the limbs, and the tail. The underside of the animal is never armored and is simply covered with soft skin and fur.[21] This armor-like skin appears to be an important defense for many armadillos, although most escape predators by fleeing (often into thorny patches, from which their armor protects them) or digging to safety. Only the South American three-banded armadillos (Tolypeutes) rely heavily on their armor for protection.
The diets of different armadillo species vary, but consist mainly ofinsects, grubs, and otherinvertebrates. Some species, however, feed almost entirely on ants and termites.
They are prolific diggers. Many species use their sharp claws to dig for food, such asgrubs, and to dig dens. Thenine-banded armadillo prefers to build burrows in moist soil near the creeks, streams, andarroyos around which it lives and feeds.
Armadillos have very poor eyesight, and use their keen sense of smell to hunt for food.[16] They use their claws not only for digging and finding food but also for digging burrows for their dwellings, each of which is a single corridor the width of the animal's body. They have five clawed toes on their hind feet, and three to five toes with heavy digging claws on their fore feet. Armadillos have numerous cheek teeth which are not divided intopremolars andmolars, but usually have noincisors orcanines. Thedentition of the nine-banded armadillo is P 7/7, M 1/1 = 32.[22]
When threatened by apredator,Tolypeutes species frequently roll up into a ball. Other armadillo species cannot roll up because they have too many plates. When surprised, the North American nine-banded armadillo tends to jump straight in the air, which can lead to a fatal collision with the undercarriage or fenders of passing vehicles.[23]
Armadillos have short legs, but can move quite quickly. The nine-banded armadillo is noted for its movement through water,[24] which is accomplished via two different methods: it can walk underwater for short distances, holding its breath for as long as six minutes; or, to cross larger bodies of water, it can increase its buoyancy by swallowing air to inflate its stomach and intestines.[25]
Gestation lasts from 60 to 120 days, depending on species, although the nine-banded armadillo also exhibitsdelayed implantation, so the young are not typically born for eight months after mating. Most members of the genusDasypus give birth to fourmonozygotic young (that is, identical quadruplets),[26] but other species may have typical litter sizes that range from one to eight. The young are born with soft, leathery skin which hardens within a few weeks. They reach sexual maturity in three to twelve months, depending on the species. Armadillos are solitary animals that do not share their burrows with other adults.[21]
Armadillos are often used in the study ofleprosy, since they, along withmangabey monkeys, rabbits, and mice (on their footpads), are among the few known species that can contract the disease systemically. They are particularly susceptible due to their unusually low body temperature, which is hospitable to the leprosy bacterium,Mycobacterium leprae. (The leprosy bacterium is difficult to culture and armadillos have a body temperature of 34 °C (93 °F), similar to human skin.)[27] Humans can acquire a leprosy infection from armadillos by handling them or consuming armadillo meat.[28][29] Armadillos are a presumedvector andnatural reservoir for the disease in Texas, Louisiana and Florida.[30][31] Prior to thearrival of Europeans in the late 15th century, leprosy was unknown in the New World. Given that armadillos are native to the New World, at some point they must have acquired the disease from old-world humans.[28][31]
The armadillo is also anatural reservoir forChagas disease.[32]
The nine-banded armadillo also serves science through its unusual reproductive system, in which four genetically identical offspring are born, the result of one original egg.[33][34][35] Because they are always genetically identical, the group of four young provides a good subject for scientific, behavioral, or medical tests that need consistent biological and genetic makeup in the test subjects. This is the only reliable manifestation ofpolyembryony in the classMammalia, and exists only within the genusDasypus and not in all armadillos, as is commonly believed. Other species that display this trait include parasitoid wasps, certain flatworms, and various aquatic invertebrates.[34]
Even though they have a leathery, tough shell, armadillos (mainlyDasypus) are commonroadkill due to their habit of jumping 3–4 ft vertically when startled, which puts them into collision with the underside of vehicles.[36] Wildlife enthusiasts are using the northward march of the armadillo as an opportunity to educate others about the animals, which can be a burrowing nuisance to property owners and managers.[33]
Armadillo shells have traditionally been used to make the back of thecharango, anAndeanlute instrument.
In certain parts ofCentral andSouth America, armadillo meat is eaten; it is a popular ingredient inOaxaca, Mexico. During theGreat Depression, Americans were known to eat armadillo, known begrudgingly as "Hoover hogs", a nod to the belief that PresidentHerbert Hoover was responsible for the economic despair facing the nation at that time.[37][38]
A whimsical account ofThe Beginning of the Armadillos is one of the chapters ofRudyard Kipling'sJust So Stories 1902 children's book.[39] The vocal and piano duoFlanders and Swann recorded a humorous song called "The Armadillo".[40]
Shel Silverstein wrote a two-line poem called "Instructions" on how to bathe an armadillo in his collectionA Light in the Attic. The reference was "use one bar of soap, a whole lot of hope, and 72 pads ofBrillo."[41]
The plates of bone are covered in small overlapping epidermal scales called scutes, which are composed of keratin.
