From Pangolins To Chickens, Exploring the World of Non-Fish Animals with Scales
Some animals are almost synonymous with the word scales, or being scaly. Most fish for example, and reptiles, come with the expectation of having scales. But there are some animals with scales that you might not expect, and not all scales are the same.
For instance, did you know that most birds have scales? and that many arthropods do too? In fact there are fish, reptilian, avian, mammalian and arthropod scales, each very different in appearance. But what are they exactly?
Well, scales are basically plates of many different shapes and sizes, made up of organic material such as keratin, dentin or collagen (amongst others). These scales form a protective layer over part or all of an animals body. They can serve a variety of functions, such as sensory, physically protective or temperature control. They are a fascinating evolutionary adaption.
We take a look at some animals with scales, across many different species in the animal kingdom, with the exception of fish. We all know fish have scales, and what they look like! Rather, we explore how different they can appear, and in many forms and fashions.
Animals With Scales
Pangolins (Family: Manidae)
Pangolins (also known as scaly anteaters) are mammals of the order Pholidota, and the family Manidae. There are 8 species in total, across three genera, They are covered in protective scales made of keratin, which the animals can not shed. It is the only mammal that is covered in these keratin scales, the same material that makes up human fingernails. The scales are made up of overlapping plates that act as armor against predators.
Most of the pangolin species live in tropical and subtropical habitats, with half the species living in Africa, and the rest in South and East Asia. One can also be found in the temperate climates of China.
They are predominantly insectivores, feeding on ants and termites using an extendable tongue. Some species will supplement their diet with small amounts of vegetation and bird eggs.
Butterflies (Sub-Order: Rhopalocera)
Butterflies are flying insects of the sub-order Rhopalocera, within the order Lepidoptera, which are an order of insects with broad wings containing minute overlapping scales. In Greek, ‘Lepidoptera’ means ‘scaled wings’.
Butterflies characteristically have slender bodies, antennae with tiny balls on the ends, six legs and four broad, usually colorful wings. Butterflies are distributed throughout the world except in the very cold and arid (dry) regions.
Butterfly wings are actually transparent – it is the over-lapping scales that give the wings the colors that we see. These scales are pigmented with melanins that give them blacks and browns, but blues, greens, reds and iridescence are usually created not by pigments but the microstructure of the scales.
Butterfly scales are made of tiny overlapping plates of setae, made of chitin, a tough and waterproof material found in the exoskeletons of insects.
Moths (Order: Lepidoptera)
Moths, make up all the other insects in the order Lepidoptera, that are not butterflies. The differences between butterflies and moths are more than just taxonomy however.
Moths tend to have thick hairy bodies and more earth tone colored wings. They are usually nocturnal – mostly active at night and rest during the day in a preferred wooded habitat. Butterflies on the other hand are mostly diurnal – active during the day.
Setae (sensory ‘hairs’) on the insects entire body (including the antennae) can feel the environment. They also give the insect information about the wind while it is flying. These sensory hairs are actually scales, though they may look like a powdery coating over their body.
While butterflies tend to have broad and flat scales, moths scales are narrower, giving them a more hair like appearance.
Crocodilians (Order: Crocodilia)
All members of the crocodilia order – crocodiles, alligators, caimans – have scales. These are not like the scales that the arthropods above have though. No, a crocodilian’s scales are in a different form entirely. There are essentially two layers to the scales on a crocodilians body. There is an underlayer of osteoderms (bony deposits formed in the dermis) and then the top layer of epidermal scales. Collectively, the layers create a type of scale known as a ‘scute’.
All reptilian scales have dermal papilla underneath the epidermal scales, but not all reptiles go on to develop osteoderms underneath the epidermal scale. In the case of crocodilians, they all develop scutes (both layers) in at least some areas of the body. These scales offer not only protection from predation, but also from the elements. They can soak up lots of heat from the sun during the day, offering protection from the cold at night, and when in the water. As these are cold blooded animals, this form of heat regulation is critical.
Turtles (Order: Testudines)
Turtles are very similar to crocodiles, in that they have two layers to their scales, the osteoderm and the epidermal layers. Though a turtle’s scales are usually smoother and less intimidating, and form in a hard shell around their body. While a turtle has scales across it’s entire body, it is the shell that is their most unique, defining and protective feature.
These shells have 2 sections, the upper ‘Carapace’ that covers their back, and is fused to their vertebrae and ribs, and the lower ‘Plastron’ which develops from the abdominal ribs, breastbone and shoulders. The Plastron is a flatter surface, whereas the Carapace is curved like a dome over their back. Both sections connect together at the sides with extensions from the Plastron section.
The ‘scute’ type of scales on a turtle are made out of keratin, the same material that hair, nails and bone are made from. They usually have 54 of these large, panel like scutes across their entire shell. Depending on the species, the shell can take on a different shape. Land turtles are more dome shaped, whereas sea turtles are flatter in general.
Chickens (Gallus gallus domesticus)
To look at a bird, you might wonder why they are on this list, but believe it or not, most birds including chickens, have scales. It shouldn’t be too much of a surprise when we remember that chickens are the closest living relative to the dinosaur!
Avian scales are different yet again, from reptilian or arthropod scales. They are made of keratin, like reptilian scales, but they are thought to have re-evolved independently from degenerative feathers, once they evolved to have a coat of feathers. On birds, scales are usually found on the legs and feet. Some, particularly birds of prey such as eagles and some owls, have feathers down to their feet, while others have scales up past the tibio-tarsal joint. It is this joint where most birds transition from feathers to scales.
Scales on chickens don’t overlap, as is true for birds in general with the exception of two – kingfishers and woodpeckers. There are three different types of avian scales: Scutella, Scutes and Cancella. Each are different in size and texture. Scutella for example, are localized to areas such as the hind part, of the chicken metatarsus. They are not as large as scutes. Cancella are the most numerous and are very small.
Anomalure – Scaly Tailed Squirrels (Genus: Anomalurus)
Anomalures are small rodents native to Central Africa. They are sometimes called scaly-tailed squirrels, but are not closely related to other ground squirrels or flying squirrels. They are the only animals in the genus Anomalurus and the subfamily Anomalurinae.
Physically, they look like many other squirrels, but with a thinner tail and wing like skin flaps, similar to other flying squirrels that evolved separately. Indeed, these squirrels are expert gliders from tree to tree, but unlike their other rodent cousins, Anomalures have scales on their tails.
These scales are organized in a keeled formation with a ridge down the centre. They only occur on the underside of their tail, with the top covered in fur, like the rest of their bodies. The scales are arranged in two rows, and they are pointy and raised.
It’s not entirely understood what advantage the scaly tail gives anomalures, but it is suggested that they aid in balance and climbing, or that they provide a level of protection by wrapping round a branch when resting in the trees.