Armadillo
Armadillos are small mammals characterized by their unique hard shells and belong to the order Cingulata, which includes twenty-one species across nine genera. These creatures are primarily found in the Americas, with the nine-banded armadillo being the sole species that extends into North America. Notably, armadillos are the only mammals with an armored shell, made of overlapping bony scales called scutes, allowing for flexibility and movement. They occupy various habitats, from rainforests to deserts, and display diverse dietary habits, being either omnivorous or insectivorous.
The evolutionary lineage of armadillos is distinct, as they share a superorder with sloths and anteaters, all of which possess additional joints in their backbones. The nine-banded armadillo has notably expanded its range in the United States, adapting to new environments despite concerns of becoming an invasive species. Additionally, they are linked to the transmission of leprosy, but the risk to humans is minimal due to widespread immunity and available treatments. Armadillos also play a role in their ecosystems, potentially controlling populations of other invasive species like fire ants. Overall, armadillos represent a fascinating example of adaptability and ecological diversity in the animal kingdom.
Armadillo
The armadillo is a type of small mammal with a distinctive hard shell that is found throughout the Americas. Twenty-one species of armadillo spread across nine genera exist, all of which belong to the taxonomic order known as Cingulata. Together with the sloths and anteaters, they form the taxonomic superorder known as Xenarthra. These otherwise seemingly dissimilar animals are categorized together because they all have extra joints in their backbones. This adaptation provides their backs and lower hips with great strength. This ability is particularly valuable to anteaters and armadillos when digging, which is one of their primary methods for obtaining food.
The vast majority of armadillo species are found in Latin America. Only one, the nine-banded armadillo (Dasypus novemcinctus), can be found north of Mexico. They range in size from the tiny six-inch-long pink fairy armadillo (Chlamyphorus truncatus), which is found in the Gran Chaco region of South America, to the five-foot-long giant armadillo (Priodontes maximus) of northern South America. The word armadillo means "little armored one" in Spanish. They are occasionally hunted by humans for their meat and shells.
Background
The animals of Xenarthra appeared on the fossil record approximately sixty million years ago. They first emerged in South America and over time split into three distinct orders of animals: the sloths of Phyllophaga, the anteaters of Vermilingua, and the armadillos of Cingulata. Many of the oldest known South American fossils are the bony plates of ancient armadillo species. After the formation of the Panamanian isthmus that linked North and South America, several species of the armadillo family Dasypodidae migrated into Central and North America. One species, the beautiful armadillo, existed in the United States until about eleven thousand years ago when it went extinct for unknown reasons. Although much bigger than the nine-banded armadillo, it shared many characteristics with its relative, including diet and body shape. This has led some scientists to speculate that the nine-banded armadillo may simply be a more recent version of the same species, although DNA evidence suggests they are likely different species.
Beginning in 1849, the nine-banded armadillo crossed into the United States and began to breed in Texas for the first time. This animal was introduced to the state of Florida in 1924, although given its subsequent spread, it likely would have independently reached this area in time. This species has become native to the central Plains of the United States and continues to expand its range to the surprise of biologists. It was previously thought that the nine-banded armadillo was too sensitive to cold temperatures to spread beyond the southern and central United States. However, this armadillo has continued to defy expectations and may be capable of reaching as far north as a line stretching from New Jersey to Iowa. Their continued expansion may be due to their high birth rate and expanding human development, the latter of which has provided them with safe, warm places to burrow. This species of armadillo annually gives birth to four identical pups that are formed from a single zygote.
Their spread has concerned biologists. Armadillos have voracious appetites and may compete with native omnivores such as skunks for food. They also have few natural predators in their new habitats, although they are often hit by cars on roadways. It is thought they may represent a severe threat to nesting sea turtles in the southeastern United States. This is a newly observed behavior and demonstrative of the highly adaptive nature of these animals. Biologists have expressed concern that this species of armadillo may develop other destructive habits in their new environments. As a result, they are sometimes classified as an invasive species. Nonetheless, it is thought they may be able to help control populations of fire ants, an even more problematic invasive species.
Overview
The armadillos of Cingulata are divided into four subfamilies: Tolypeutinae, Euphractinae, Chlamyphorinae, and Dasypodinae. The seven species of Tolypeutinae are known for their shared diet of social insects such as termites. Euphractinae has five members that are covered in thick bristle-like hairs. Chlamyphorinae consists of two species especially adapted to digging, with thick forearms and large claws. The seven species of Dasypodinae are distinguished by their long noses and naked tails.
The most distinctive shared feature of armadillos is their flexible armor that encases most of their bodies. They are the only mammals in the world to have an armored shell. This leathery armor covers the top of its head, tail, and the upper parts of its legs. It is composed of a series of hard bands—the number of which varies between species—with softer skin between the bands that expands and contracts depending on the position of the animal. This unique construction of armor allows armadillos a greater range of movement than a simple hard shell provides. The armor itself is composed of a series of small scales known as scutes that overlap each other. These scales are made of bone that is covered with a horn-like material called keratin—the same protein that makes up human fingernails.
Beyond these shared characteristics, the shells of armadillos vary widely between species. For instance, the southern three-banded armadillo (Tolypeutes matacus) and the Brazilian three-banded armadillo (Tolypeutes tricinctus) have only three bands, while the screaming hairy armadillo (Chaetophractus vellerosus) has eighteen bands. The aforementioned three-banded species of Tolypeutes are the only species capable of fully rolling themselves into balls, while the two species of fairy armadillos in the subfamily Chlamyphorinae have upper-body shells that are fused to their pelvis and spine.
Armadillos are highly adaptable. They are either omnivorous (eating both plants and animals) or insectivorous (mostly eating insects). They fill a variety of ecological niches and can be found from the central Plains states of Nebraska and Kansas to southern Argentina. They are known to live in environments ranging from the rainforests of the Amazon to the various deserts of the Americas. The pichi (Zaedyus pichiy) is even able to tolerate the cold temperatures of southern Argentina. The pichi is also the only armadillo that hibernates.
Nine-banded armadillos are the only other known animal besides humans capable of carrying leprosy. These animals have been linked to the spread of the disease in humans in a few isolated cases in the United States. However, 95 percent of humans are immune to this disease and effective treatments exist, so the threat of human infection is relatively low. Nevertheless, this unique trait has made armadillos an effective lab animal in studies of leprosy.
Eric Bullard
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