There are 23 species of crocodile – most live in fresh water rivers and lakes but some live in salt water and the saltwater crocodile is the largest species of crocodile and the world’s largest reptile. They can be found in all inhabited continents with the exception of Europe. The first crocodiles appeared around 250 million years ago, at the same time when dinosaurs appeared. Crocodiles can be often seen with their jaws wide open. They open their jaws to cool themselves because they don't have sweat glands.