Crocodiles are large semi-aquatic reptiles that first appeared 55 million years ago and still live in tropical regions around the world today. There are 23 crocodile species that can be found in various environments like lakes and rivers. Crocodiles were apex predators 100 million years ago during the Mesozoic era, and factors like temperature determine the sex of crocodile hatchlings. Crocodiles have powerful jaws and teeth and eat by swallowing food whole without chewing.