Modern zoology acknowledges more than 10,000 species of reptiles living on all continents except for Antarctica, and even though each of these species has unique evolutionary features, they all have one thing in common: scales. This coating that covers reptiles’ skin is a complex evolutionary feature that has been serving specific functions for millennia, adapting to environmental factors and helping reptiles survive and thrive. But what exactly are scales and why do reptiles have them?
Contrary to common belief, scales are not skin. They are a distinctive feature found in all reptiles, they grow on the skin and they cannot be detached, like in the case of fish. Scales, or scutes, as they are also called, are made of keratin, a protein also found in the human body.
How did scales appear in reptiles?
The earliest species of reptiles date back to 320–310 million years ago, but they did not have scales at first. This happened much later, in the Mesozoic era, when they evolved considerably and became more widespread, which is why zoologists refer to this era as The Age of Reptiles. Scales are believed to have developed in this period, as a random genetic mutation that helped reptiles adapt to the environment and protect themselves from their natural predators.
Types of scales
Scales size, shape, colour, structure and function varies from species to species.
- Lizards have tubercular or overlapping keratinised scales, sometimes with bony plates underneath. Scales can be thicker or thinner depending on the area of the body.
- Snakes are completely covered in scales, which play a vital role in movement and protection. Each species of snakes has unique scales, which is one the criteria we use to identify them.
- Crocodiles & turtles have a different type of scales called scutes. These are formed in the deeper layers of the skin and serve as a sort of armour. Some birds and mammals present similar scutes on their feet and tails, leading us to believe that they share the same ancestor with crocodiles and turtles.
General functions of reptile scales
This function is best observed in the case of snakes, which use the scales on their bellies to quickly slide on rough surfaces.
Provide protection from predators
This function is found in most species of reptiles and is one of the factors that has encouraged their evolution. Scales can be extremely strong, preventing predators from attacking reptiles without injuring themselves. There is even a species of non-venomous snakes whose scales perfectly resemble the pattern of a venomous snake, which keeps predators at bay.
Scales serve as a water storage space for reptiles living in the desert. Thus, water does not evaporate through the skin, as it happens with many other animals. Instead, it remains under the scales, keeping reptiles cool and hydrated even in extremely hot temperatures.
Some reptiles, such as chameleons and geckos, are famous for using their scales to blend in with their surroundings. This evolutionary camouflage has two functions: it helps them hide from predators and also take their prey by surprise.
Why do reptiles moult their scales?
Scales moulting, or ecdysis, is extremely common in the world of reptiles. Through moulting, old cells are replaced with new ones and thus the “armour” is regenerated. This is also a good way to get rid of parasites. Most species shed in flakes, but snakes shed all their scales at once. Something interesting happens in the case of rattlesnakes: when the old layer unpeels, it sticks to the end of the tail, producing the famous rattling sound that warns predators. Depending on the age of the snake, moulting can occur anywhere from one to four times a year and, when this happens, the snake is vulnerable and retreats to a safe hiding space.