Big Hairy Armadillo

Big Hairy Armadillo
Big Hairy Armadillo
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cingulata
Family: Dasypodidae
Genus: Chaetophractus
Species: C. villosus
Binomial name
Chaetophractus villosus
(Desmarest, 1804)
Big Hairy Armadillo range

Chaetophractus villosus, commonly called the Big Hairy Armadillo (of the family Dasypodidae) is one of the largest and most numerous armadillos in South America. It lives from sea level to altitudes of up to 1,300 meters across the southern portion of South America and can be found in grasslands, forests, savannahs, and has even started claiming agricultural areas as its home. It is an accomplished digger and spends most of its time below ground. They make both temporary and long term burrows depending on their food source.[1] The armadillo can use specially evolved membranes in its nose in order to obtain oxygen from the surrounding soil particles without inhaling any of the soil itself.[2] Armadillos are protected from predators by a series of thin bony plates along the head and back. They reach sexual maturity at around nine months and have been known to live over thirty years in captivity. Though this animal is routinely harvested for its meat and its shell, or simply killed for pestering farmers, it has shown amazing resiliency and populations seem to be handling this exploitation well. Because of this there are currently no protective practices in place for this armadillo but it does live in many protected areas. This species of armadillo is a preferred research animal due to its adaptability to the lab setting, and relative hardiness in situations of stress.[3]


Species Description and Taxonomy

Chaetophractus villosus or Big Hairy Armadillo is the most abundant species of armadillo in Argentina. The armadillo’s head and body are covered by protective bony plates, with its head plate being the most prominent. Along its back, flexible bands that encircle the torso allow flexibility in this otherwise stiff armor. The underside of this armadillo is densely covered in hair and this trait is how it got its common name. Long course hairs also project from the bony plates making this armadillo much hairier than its cousins. The average individual grows anywhere from 260 mm to 340 mm in body length by the time it reaches maturity. Powerful front claws are used for both foraging and avoiding predators.[4]

The genus Chaetophractus consists of two species, Chaetophractus vellerosus (Lesser Hairy Armadillo) and Chaetophractus villosus. These species are recognized by the large amount of hair that extends all over their body, but especially on their underside. The skulls follow the same patterns as other dasypodids however females exhibit longer bones in the rostrocaudal plane which is one of the key variables that shows the sexual dimorphism of these species. Not much is known about the cranial morphology of these species especially bone by bone descriptions. More research is being done in order to better describe these species and the skeletal differences between them. For the time being, body size, habitat, and behaviors, are the best way to discern the differences.[5]


When trying to determine the differences between these species of Chaetophractus a few noticeable traits stand out. The first difference is the size of these species, Chaetophractus villosus being the biggest, which can grow to a length of 340 cm. Chaetophractus vellerosus is much smaller, being able to fit in the palm of your hand when full grown, usually weighing only a kilogram. Both species are covered with much more hair than any other armadillos, mostly sprouting from its underside or between the bony plates along its back. When Chaetophractus villosus is sexually aroused with an erect penis it is easy to determine its species. Its penis can be as long as 35 cm long and usually remains completely withdrawn inside a skin receptacle. The Lesser Hairy Armadillo can usually be found in higher altitudes because its smaller size and slower metabolic rate helps it survive in an area that has less food.[6]

Fossil Record

The presence of a carapace containing osteoderms is one of the very distinctive features of armadillos and is true for fossil taxa as well. These elements are evident frequently in the paleontological record due to their resilience. Three distinct areas are recognized in these hardened plates. The outer and inner parts are made of thin compact bone, while the middle zone is thicker and contains tissues for hair follicles and sweat glands. The presence of red bone marrow is rare in members of Chaetophractus and yet widespread in Dasypus novemcinctus osteoderms. These findings propose an early split of both subfamilies and maintain the hypothesis that the Euphractinae are more derived than the Dasypodinae.[7]

Chaetophractus villosus earliest known fossils were found in the Pampean region which suggests that it is where the species originated. Fossil records then indicate the migration into Patagonia as the main dispersal route, which most likely occurred after the Pleistocenic glaciations. Using molecular dating scientists estimate that the first armadillos popped up aroud the Cretaceous/Tertiary boundary. This was followed by the divergence of anteaters and sloths in the Early Eocene era.[8]

Geographic Distribution

Chaetophractus villosus home range encompasses the Pampas and Patagonioa as far south as Santa Cruz, Argentina and Magallanes, Chile. It is found in the Grand Chaco of Bolivia, Paraguay, and Argentina and is starting to migrate south into the Tierra del Fuego province of Argentina as well. It can be found in the Bio-Bio province and south to Aisen province both in eastern Chile. Climate change and the opportunistic tendencies of this armadillo are allowing them to live in more and more areas. Unlike some of its cousins the Big Hairy Armadillo has not had as drastic of a change in its territory. This does not mean that this armadillo isn’t as affected by climatic change it just hasn’t migrated as far north as some other species.[9]


Members of Dasyposidae including Chaetophractus villosus have evolved very interesting and specific traits in order to help it survive. The most recognizable of these are the bony plates that cover the armadillos head and back. These protective plates allow the individual a fair measure of protection against its natural predators. This armadillos also has a remarkable respiratory adaptation when the nostrils are completely covered in soil. It is able to maintain sufficient respiratory movements due to a mechanism that allows it to use air that fills the space between soil particles, without inhaling the particles themselves. This along with its powerful digging claws and low body mass ratio contribute to this fossorial, or subterranean, lifestyle. Even with the added challenge of burrowing this armadillo maintains similar body mass ratios with non fossorial species and suggests that it has adapted to a burrowing lifestyle as a way to avoid extreme temperatures and predators, rather than any help it could receive from foraging.[10]

Little is known about the haemostasis of this species. Platelet counts are similar between sexes and they seem to remain similar even when in captivity. They are comparable to most other mammals and react in the same manner to proven agonists. More studies in this area could reveal biomedical advances but at the moment little is known.[11]

Scientists conducted studies on the Chaetophractus villosus penis muscles revealed that this species very long penis exhibits variability. During its waking hours it remains hidden beneath a skin receptacle, until it becomes erect and it projects outside in a rostral direction. During its slow wave sleep phase penile protrusion makes some very complex movements. The penis during this phase is non-erect but remains outside of its receptacle. During paradoxical sleep, no erections occur, and the penile muscles share the characteristics of the rest of the body.[12]

Life History and Behavior

In Patagonia there is a large species diversity among the fauna. This is due to the diverse habitats on both the Chile and Argentinean sides of the Andes Mountains and the species that have evolved for each environment. Of these the rodents represent fifty percent of the mammalian population and carnivores another twenty-three percent. This armadillo has even been able to do quite well in captivity and become tame relatively quickly.[13]

Chaetophractus villosus spends most of its time burrowing in the ground and looking for insects or worms as its main foraging method. Its powerful front claws and snout allow it to rout through the sediment with relative ease. When the armadillo detects a predator it will run to the nearest burrow and wedge itself in using its legs. In this way predators are left with nothing but the bony plates exposed. When it cannot get to one of its burrows it will lay down flat on the ground in order to better protect its softer underside.[14]

Most of this armadillo’s activity occurs starting at dusk and continues on into the night. They can be seen active in the day, however, when enough food cannot be found during the night. It uses its sense of smell to find prey and shovels soil away in order to reach it. Most individuals breed in the late winter or spring but in captivity have been known to conceive year round. After a gestation period of 60 to 75 days the female will usually give birth to a litter of one to two young which are suckled for another 50 to 80 days.[15]

Chaetophractus villosus seems to be able to burrow through most sediment but tends to shy away from rockier terrains. It would also appear that they tend to burrow into the side of a hill rather than on flat ground. These armadillos make temporary burrows in search of food or safety that are usually shallow and less complex. Their home burrows are usually much deeper and can be quite complex, with many escape tunnels and dens. The orientation of their burrows depends largely on the wind orientation. This allows them to be well adapted to arid desert terrain.[16]


Chaetophractus villosus is one of the armadillo species that is not in danger of extinction at the moment. In fact on the endangered species scale this armadillo rates as a LC or least concern species. This is due to its large population and widespread habitat range. It also has a remarkable ability to adapt to many changing environments. It is considered a least concern species because it is not predicted to decrease into any of the threatened categories any time soon. In fact the Big Hairy Armadillo populations seem to be growing.[17]

Because of the large amount of biodiversity in these regions many temperate ecoregions are now under protection. By not only protecting individual species but also the habitat that they live in, many species can benefit from these protected areas. This ensures that the species that live in them can maintain a diverse ecosystem and gives them a sanctuary limiting the influence of man. Without this protecting individual species would be a challenge due to loss of habitat or other influential variables.[18]


  1. ^ "Journal of mammology" Brian K. McNab
  2. ^ "The vomeronasal organ of the South American armadillo Chaetophractus vilosus (Xenarthra, Mammalia): anatomy, histology and ultrastructure" P.D. Carmanchahi, et al.
  3. ^ "Effects of land use on the distribution of three specie of armadillos in the Argentinean Pampa." Agustin M Abba, et al
  4. ^ "Effects of land use on the distribution of three specie of armadillos in the Argentinean Pampa." Agustin M Abba, et al
  5. ^ "Evolutionary trends of the histological pattern in the teeth of edentata (xenarthra)" J Ferigolo, e al
  6. ^ "New data on armadillos (Xenarthra: Dasypodidae) for Central Patagonia, Argentina." Agustin M. Abba, et al.
  7. ^ "American society of mammalogists" Brian K. McNab
  8. ^ "American society of mammalogists" Brian K. McNab
  9. ^ "Effects of land use on the distribution of three specie of armadillos in the Argentinean Pampa." Agustin M Abba, et al
  10. ^ "Evolutionary trends of the histological pattern in the teeth of edentata (xenarthra)" J Ferigolo, e al
  11. ^ "Fibrinolytic system of the armadillo Chatophractus villosus (Xenarhra, Dasypodidae)"Juan Tentoni, et al.
  12. ^ "Absence of penile erections during paradoxical sleep. Peculiar penile events during wakefulness and slow wave sleep in the armadillo." Jorge M. Affanni, et al.
  13. ^ "Effects of land use on the distribution of three specie of armadillos in the Argentinean Pampa." Agustin M Abba, et al
  14. ^ "American society of mammalogists" Brian K. McNab
  15. ^ "American society of mammalogists" Brian K. McNab
  16. ^ "Effects of land use on the distribution of three specie of armadillos in the Argentinean Pampa." Agustin M Abba, et al
  17. ^ "New data on armadillos (Xenarthra: Dasypodidae) for Central Patagonia, Argentina." Agustin M. Abba, et al.
  18. ^ "Effects of land use on the distribution of three specie of armadillos in the Argentinean Pampa." Agustin M Abba, et al

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