Chaetophractus villosus (Desmarest, 1804)

Common Name and Abundance

Chaetophractus villosus, commonly known as the big hairy armadillo, is the most abundant armadillo species in Argentina.

Bony Armor Structure

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.

Common Name Origin

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.

Body Length

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).

Weight

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).

Tail Length

The tail measures 9 to 17 cm (3.5 to 6.7 in) long.

Claw Function

Powerful front claws are used both for foraging and escaping predators.

Nasal Adaptation

This armadillo has specially evolved nasal membranes that let it obtain oxygen from surrounding soil particles without inhaling soil itself.

Genus Species Composition

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.

Genus Identifying Trait

All species in this genus are recognized by the large amount of hair covering their bodies, especially their undersides.

Skull Sexual Dimorphism

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.

Cranial Morphology Research Gap

Little is known about the cranial morphology of these Chaetophractus species, particularly when it comes to bone descriptions.

Species Identification Methods

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.

Natural Range

The natural home range of C. villosus covers a continuous area across large parts of Argentina, Bolivia, and Paraguay.

Argentine Range Extent

In Argentina, its natural range extends beyond the Pampas, reaching as far south as Santa Cruz Province in southern Patagonia.

Tierra del Fuego Introduction

The species was introduced to Tierra del Fuego Island in 1982, spreading from a property northeast of Río Grande.

Introduced Population Adaptation

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.

Family Classification

C. villosus is a member of the family Chlamyphoridae, and its members, including C. villosus, have evolved distinct specialized traits to support survival.

Armor Protective Function

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.

Soil Respiration Adaptation

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.

Fossorial Lifestyle Adaptations

Along with its powerful digging claws and high surface-area-to-mass ratio, this adaptation supports its fossorial, or subterranean, lifestyle.

Surface-Area-to-Mass Ratio

Even with the added challenges of burrowing, this armadillo maintains similar surface-area-to-mass ratios as non-fossorial species.

Burrowing Adaptation Purpose

This suggests it adapted to a burrowing lifestyle to avoid extreme temperatures and predators, rather than to support foraging.

Hemostasis Research Gap

Little is known about hemostasis in this species.

Platelet Count Characteristics

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.

Hemostasis Research Potential

More research in this area could lead to new biomedical advances, but little additional information is currently available.

Penis Muscle Study Findings

Studies of C. villosus penis muscles have found the species' very long penis has variable traits and behaviors.

Waking Penis State

During waking hours, the penis stays hidden inside a skin receptacle, only projecting outward in a rostral direction when it becomes erect.

Slow Wave Sleep Penis Behavior

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.

Paradoxical Sleep Penis State

During paradoxical sleep, no erections occur, and the penile muscles share the same characteristics as the rest of the body's muscles.