Reptiles – Types & Characteristics
Sometimes loved and sometimes hated, reptiles have a special place in the Animal Kingdom. They are a diverse group of animals that appeared some 300 million years ago during the Carboniferous period.
They range from tiny lizards to massive crocodiles, with no less than 10,000 species in between! Reptiles are amazing animals and remarkably well-adapted to their environments.
On this page, we will learn more about them, what are the characteristics that make them unique, the different types of reptiles that exist on our planet, and much more.
Ready to learn lots of interesting facts about reptiles? Read on!
7 Characteristics of Reptiles
- Cold-blooded: Reptiles are cold-blooded (ectothermic) animals. Their body temperature is conditioned by the temperature of the environment around them. Unlike mammals and birds, they are not able to produce their own heat and regulate their body temperature internally.
- Scales: Reptiles have dry skin covered with scales, acting as a protection layer. Scales are made of beta keratin, a different type of keratin than the one making up our hair or our nails. This creates impermeable skin that makes it impossible to be used to breathe in water: it is an adaptation for reptiles to leave the water and become terrestrial over the course of evolution.
- Lungs for respiration: Reptiles breathe with lungs (they all have at least one), unlike amphibians who are also able to breathe through their skin.
- Mostly oviparous: Most reptiles lay amniotic eggs – they are amniotes. It means that the eggs contain an amnion, a series of membranes filled with amniotic fluid, in which the embryo develops. The eggs have a hard shell and are fertilized internally. This allows reptiles to lay eggs on land, unlike amphibians who need water to lay their eggs. There are just a few species of lizards that directly give birth to living young.
- Three-chambered heart: Apart from crocodilians which have a four-chambered heart, most reptiles have a three-chambered heart with two atria and one ventricle. This allows an efficient separation of oxygenated and deoxygenated blood, but not as efficient as with four-chambered hearts. Their metabolism being slower, they actually don’t need the extra efficiency a four-chambered heart would provide.
- Tetrapods: Reptiles are tetrapods – which means they have four legs. Snakes and limbless lizards are still considered tetrapods because their ancestors were tetrapods.
- Water conservation adaptations: Reptiles’ kidneys are different from mammals’ kidneys. Instead of urine, they produce uric acid in a concentrated, solid way, and they are able to reabsorb a large part of their water.
These adaptations allowed reptiles to conquer land and have a terrestrial lifestyle. From their mode of reproduction to their skin and kidneys, reptiles are able to conserve water and live in various, sometimes harsh environments, in most parts of the planet.
The 4 Types of Reptiles
The class Reptilia contains 4 orders: Crocodilia (crocodilians), Squamata (lizards and snakes), Testudines (turtles), and a fourth order, Rhynchocephalia, that is only made of two species: the tuataras, which are endemic to New Zealand. Let’s take a look at these 4 orders and their characteristics.
Crocodilians (order Crocodilia)
Crocodilians are semi-aquatic predators with a long and flat snout, with nostrils and eyes on the top of their heads, allowing them to breathe and see while swimming.
Often referred to as “crocodiles”, this group includes true crocodiles, but also caimans, alligators, gharials, and false gharials.
They are known for their powerful jaws and their powerful tails. It is an undulating movement of their tail that enables them to swim.
Lizards and Snakes (order Squamata)
Squamata is not only the largest group of reptiles (by far) but also the second-largest order of vertebrates. Members of this order include geckos, agamas, chameleons, iguanas, monitor lizards, skinks, all snakes (among others).
Reptiles of this group are often called scaled reptiles, they have their body covered with scales and need to molt periodically. They also have flexible jaws that enable them to open their mouth very wide and swallow large prey.
Turtles (order Testudines)
The most obvious characteristic of the order Testudines is the presence of a specific shell made of a carapace covered with scales on the back, and a plastron on the belly. This order comprises all the turtles and tortoises.
Turtles are famous for being slow-moving animals on land. In the water, however, they are able to swim pretty fast thanks to their streamlined body. Most turtles are omnivores.
Tuataras (order Rhynchocephalia)
Tuataras, with their lizard appearance, look like they could belong to the order Squamata. But they belong to their own order, Rhynchocephalia. It is a more ancient group with mostly extinct members, with the exception of two species, Sphenodon punctatus and Sphenodon guntheri – the tuataras.
Without going into too much detail, tuataras differ from squamates by several anatomic traits and some characteristics they share with birds.
Frequently Asked Questions About Reptiles
Are All Reptiles Cold-Blooded?
Yes, all reptiles are cold-blooded, or ectothermic. Their body temperature depends on the temperature in their immediate environment, and they can’t regulate their body temperature internally, unlike mammals or birds.
Do Reptiles Have Emotions?
Yes, studies have shown that reptiles are able to feel a range of emotions such as anxiety, pleasure, pain, fear, or stress.
Why Do Reptiles Shed? Do All Reptiles Shed?
Reptiles grow in size over time, but their skin does not. As a result, they regularly have to shed their skin which has become too small to contain their body. It is also an opportunity to get rid of any parasites or damaged parts of the skin. All reptiles shed their skin as they grow larger.
Do All Reptiles Lay Eggs?
Most reptiles lay eggs on land. There are a few notable exceptions, such as all boa species, many vipers, and some species of skinks. Instead of laying eggs, they give birth to live young.
Do Reptiles Sweat?
No, reptiles have dry skin. They do not have sweat glands and can’t sweat.
How Long Do Reptiles Live?
Squamates have the shortest lifespan: snakes and lizards usually live around 5 years, sometimes up to 10 years.
Crocodilians live much longer, on average between 30 and 50 years, or more if they live in captivity. The Nile Crocodile can even reach 100 years.
Tuataras are also able to reach the venerable age of 100 years.
Turtles and tortoises are the reptiles with the longest lifespan. Some giant tortoises in Seychelles and the Galapagos Islands are known to be at least 250 years.
Do Reptiles Feed Their Young Milk?
No, reptiles do not feed their young with milk, as this is a characteristic of mammals. Reptiles don’t have a mammary gland and do not produce milk.
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