CRETACEOUS to PLEISTOCENE PERIOD: 80 million - 10,000 years ago
The modern crocodiles of today have remained unchanged since the days of the dinosaurs. Crocodiles belong to the family Crocodylidae. Although this family has existed since the upper Triassic Period, over 200 million years ago, reptiles which can definitely be classed as modern crocodiles only appear in the fossil record about 80 million years ago.
The crocodile's eyes and nostrils are on top of the head so it can see and breathe while the rest of it is underwater. As an added advantage, its ears and nostrils can close when it dives, and a nictitating membrane (a transparent eyelid) closes over the eye to keep water out.
Crocodiles swim mostly with their tails. Though their back feet are webbed, they rarely use them underwater. On land, they use their powerful legs to move around. They only look slow; Nile Crocodiles have been known to "gallop" at speeds of about 30 miles an hour.
Although crocodiles look like alligators, they can be distinguished by their longer, narrower snout, and their fourth tooth, which sticks out from the lower jaw rather than fitting neatly into the upper jaw. The adults can reach lengths of over 10 feet and can weigh up to 1500 pounds.