Reptile

Reptiles are a fascinating group of animals that include turtles, crocodiles, lizards, snakes, and the tuatara. They are known for their unique way of regulating body temperature—they rely on external sources like the sun to warm up, which makes them ectothermic. With over 12,000 different species, reptiles live on every continent except Antarctica and come in many sizes, from tiny geckos to massive crocodiles.

Unlike amphibians, reptiles do not need water to reproduce. They lay shelled eggs on land, which allows them to live in dry and even desert environments. Some reptiles, like certain snakes and lizards, give birth to live young instead of laying eggs. This ability to live away from water sets reptiles apart and lets them thrive in many different habitats around the world.

Reptiles have a long history, with their ancestors appearing during the late Carboniferous period. Over time, they evolved into many forms, some of which, like the dinosaurs and flying pterosaurs, went extinct millions of years ago. Today, reptiles continue to be important parts of ecosystems, helping control insect populations and serving as prey for other animals. The study of reptiles, along with amphibians, is called herpetology.

Classification

See also: List of reptiles

The idea of grouping animals called reptiles started in the 13th century when people noticed creatures like snakes, lizards, and even some strange monsters. Early scientists grouped these reptiles with amphibians, but by the 19th century, scientists realized they were different kinds of animals.

Today, scientists understand that reptiles share features like laying eggs with tough shells, but they are not all closely related. Birds, for example, are actually closer to crocodiles than to lizards or snakes. Modern science uses family trees to show how these animals are related, showing that turtles are closely related to crocodiles and birds.

Evolutionary history

Main article: Evolution of reptiles

Reptiles first appeared about 310–320 million years ago during the late Carboniferous period. They evolved from early four-legged animals called reptiliomorphs. One of the oldest known reptiles is Hylonomus, a small, lizard-like creature about 20 to 30 centimetres long that lived around 315 million years ago.

During the Carboniferous period, reptiles began to thrive, especially after a major change in the environment called the Carboniferous Rainforest Collapse. This event made life harder for amphibians, which need water to lay eggs, but helped reptiles because their eggs could be laid on land. Reptiles started to diversify and fill new roles in nature, leading to the "Age of Reptiles" in the Mesozoic era. This was a time when reptiles, including dinosaurs and pterosaurs, dominated the Earth.

Morphology and physiology

Reptiles have unique ways of moving blood through their bodies. Most lizards and snakes, along with turtles, have hearts with three chambers — two atria and one ventricle. This helps them mix oxygen-rich and oxygen-poor blood, which can be useful for diving or staying warm. Crocodiles, however, have hearts with four chambers, similar to birds and mammals.

Reptiles are often called “cold-blooded” because they don’t generate much internal body heat. Instead, they rely on sunlight or warm surfaces to regulate their temperature. This means they don’t need to eat as much as warm-blooded animals like birds or mammals. Some large reptiles, like leatherback turtles, can stay warm enough just by moving around, a process called gigantothermy.

Reptiles breathe using lungs, and each group has its own way of doing this. For example, crocodiles have a special muscle that helps their lungs expand, while turtles use muscles connected to their shells to breathe. Most reptiles can hold their breath for long periods, especially those that live in water.

Reptiles have dry, scaly skin that helps prevent water loss, allowing them to live in dry places. They shed their skin periodically, a process called ecdysis, which helps them grow. Their digestion is simple, as they mainly eat meat, which is easier to break down than plants. Some reptiles, like turtles, eat plants and swallow small stones to help grind up their food.

Many reptiles have excellent vision, especially in daylight, and some can even see ultraviolet light. They also have other senses, like the ability to detect heat, which helps snakes find prey in the dark. Most reptiles lay eggs with protective shells, though some give birth to live young. Reptiles can live for many years, with some tortoises known to reach over 100 years old.

Cognition

See also: Animal cognition

Reptiles used to be thought of as less smart than mammals and birds, but we now believe this might be because of old research methods and focusing too much on brain size. Even though their brains are smaller compared to their bodies, bigger reptiles can show clever behaviors. For example, large lizards like monitors can work together and remember good hunting spots. Crocodiles also have complex social lives. The Komodo dragon can play, and turtles can be social too, sometimes staying faithful and sometimes not. Studies show that wood turtles can solve mazes better than rats, and giant tortoises can learn new things and remember them for a long time. Even sea turtles, thought to have simple brains, use their flippers in smart ways to find food.

There is also evidence that reptiles can feel emotions such as anxiety and pleasure.

Defense mechanisms

Reptiles like snakes and lizards often try to avoid danger by running away. When they can't escape, many use camouflage to blend into their surroundings. Some reptiles, like the blue-tongued skink and the frill-necked lizard, show bright colors to scare off predators. Rattlesnakes make loud noises by shaking their tails to warn off attackers.

Some reptiles, such as certain snakes, use venom to defend themselves. When threatened, they may spread out their necks or hiss loudly. Crocodiles and alligators show their teeth and make hissing sounds to look scary. If needed, they might attack with a powerful bite.

Many lizards, like geckos, can lose their tails to escape from predators. The tail continues to move, distracting the predator while the lizard runs away. Though the tail can grow back, it will be different from the original.

Relations with humans

Further information: Human uses of reptiles

In cultures and religions

Snakes and turtles have important meanings in many cultures and religions. In ancient Egypt, the Nile cobra was worn on the crown of the pharaoh and was worshipped as a god. In Greek stories, snakes are linked to powerful symbols and heroes. In Hinduism, snakes are respected and sometimes worshipped, seen as symbols of fertility and protection. In Mesoamerica, snakes were important in the beliefs and art of ancient people. In the Bible, a snake plays a key role in the story of Adam and Eve.

The turtle is a symbol of calm and strength in many cultures around the world. Its long life and protective shell have inspired stories and beliefs for thousands of years. In some traditions, a giant turtle is said to hold up the world or the sky.

Medicine

See also: Epidemiology of snakebites

Snake venom has been studied for its possible uses in medicine. Some parts of snake venom might help treat diseases like cancer. Substances from the Gila monster, a type of lizard, are used in medicine to help people with diabetes. Geckos have been used in traditional medicine, though scientists have not found proof that they work. Turtles have also been used in traditional medicine for thousands of years, but there is no scientific proof that their parts have any health benefits.

Commercial farming

See also: Crocodile farm, Snake farm, and Turtle farming

Crocodiles are often farmed to provide leather for shoes and bags, and their meat is also eaten. Farming crocodiles has helped protect some wild populations. Snakes are also farmed, mainly in East and Southeast Asia, for their meat, skin, and for making antivenom. Turtle farming is controversial because it can increase demand for wild turtles and may spread diseases to wild populations.

Reptiles in captivity

Further information: Herpetoculture

Some people keep snakes, lizards, and turtles as pets. Popular pets include ball pythons, corn snakes, bearded dragons, iguanas, and geckos. Turtles and tortoises are also common pets, but they need special care, including the right temperature and diet. Because reptiles can carry harmful bacteria, owners must wash their hands after handling them.