Reptiles

All reptiles are covered in scales, a trait that separates them from other land animals. Made of keratin, scales provide protection and prevent water loss. Some reptiles, like snakes, use them for locomotion. They can also help with camouflage or, if brightly colored, serve as a warning against potential predators. Reptiles are ectothermic, or cold-blooded, meaning their body temperature is regulated by their environment.

Because they don't regulate their own body temperature, reptiles have few energy requirements and can go for long periods without food. They also expend less energy than warm-blooded animals and tend to move less. But move they do, mostly by crawling or slithering. Many can climb trees, and some even glide from branch to branch. Some, like sea turtles, sea snakes and crocodiles, swim through water. A couple can even run on top of water.

With few exceptions, reptiles are carnivorous animals. Their smooth-edged, pointy teeth are designed for grabbing prey, and a backward curve ensures struggling animals don't get away. Unlike mammals, reptiles lack teeth that are specialized for chewing; instead, they tend to swallow their prey whole or in large chunks. Venomous snakes have large, hollow fangs that deliver a cocktail of toxic proteins to their victim.

There are around 8,240 reptile species on the planet today. Most of these are snakes and lizards; together with amphisbaenians (limbless, worm-like lizards), they number around 7,900 species. Turtles, tortoises and terrapins (those that live in fresh or brackish water) number about 300 species. Crocodilians (crocodiles, alligators, gavials and caimans) account for 23 species, including the world's largest reptile, the saltwater crocodile. The final reptile order includes two species of tuatara — lizard-like creatures with a spiny crest that are native to New Zealand