Scales, Scutes, and Skin

Scales, Scutes, and Skin
Tough skin and scales may be unusual in snails. However, they are typical armor for many other animals.

Armadillos, for example, are armor-plated mammals that live in Central and South America, as well as in parts of the southern United States. Their name, which means “little armored one” in Spanish, refers to their bony armor. Scientists call the armadillo’s armor a carapace.

The carapace is made up of bony plates arranged in bands around the armadillo’s body. The plates are covered by tough skin. Each bony band is separated from the ones next to it by a band of skin, allowing the armadillo to flex its body. The armadillo found in the United States is called the nine-banded armadillo. Its armor covers its head, body, legs, and tail. Only its belly and ears are unprotected.

If a coyote or other predator threatens it, a nine-banded armadillo’s first defense is to flee. It zigzags as it runs away. If it cannot run away, it digs with its strong claws. It burrows into the ground in less than two minutes. The predator may pull on the armadillo’s tail to yank it out of the burrow. This won’t work because the armadillo hangs on with its claws. Its bony bands also help wedge it in place.

A nine-banded armadillo can also hunker down so that its carapace touches the ground. Then it can pull in its nose and feet. Playing dead or leaping abruptly into the air are other defenses. It can also curl its body slightly so that its nose and tail touch, though it cannot roll up into a ball.

The nine-banded armadillo is about the size of a cat. The pink fairy armadillo is much smaller—about as long as a dollar bill—but it is also a mighty digger. Like its larger cousin, it can swiftly dig a burrow when danger threatens. It runs into the burrow head first and plugs the opening with a plate of armor that covers its hind end.

The three-banded armadillo is the only armadillo that can roll itself up so tightly that it looks like a scaly croquet ball. This armadillo can also unroll slightly to peek out and see if its attacker is still there. If the attacker comes close to investigate, the armadillo quickly slams its carapace shut again—an action that sometimes nips the attacker’s nose.

In parts of Africa and Asia, scaly mammals called pangolins rely on protective body armor for defense, too. A pangolin is a long-tailed, ant-eating, nocturnal animal covered in a heavy coat of thick, overlapping scales. Only its belly and part of its face are exposed.

Unlike armadillos, all species of pangolin are able to roll into a tight ball. The scales also stand on edge so that they resemble spikes. If a predator pokes its nose between the scales, the pangolin can move so that the sharp scales pinch. All the while, glands under the pangolin’s tail produce a bad-smelling fluid.

Animal armor also includes the bony scales of fish. Fish scales overlap to form a flexible but strong covering. The squared-off bodies of boxfish have scales that link together to make a boxy suit of armor. A boxfish’s tail, fins, eyes, and mouth stick out of the box.

Sharks have skin covered with tiny, sharp teeth called “skin teeth” or dermal denticles. The denticles make the skin as rough as sandpaper. A shark’s skin is like a strong but flexible suit of chain mail. A great white shark’s skin is so dense with denticles that it even helps protect it from the bites of other sharks.

Crocodiles and alligators also have armor-like skin. Like other reptiles, they have tough, horn-like scales in their skin. Unlike most other reptiles, they also have strong bony plates embedded in the skin.

A rhinoceros does not have scales, but it does have thick skin. A rhino’s skin ranges from about three-quarters of an inch (18 mm) deep in some places to nearly 2 inches (45 mm) on its shoulders. This helps protect a rhino from a predator’s fangs and claws. The rhino also has a formidable horn. The only rhino likely to be attacked by a predator is an unguarded calf.