Crocodiles are one of the planets oldest living creatures, thought to be around 200 million years old which means that crocodiles were around in dinosaur times. As crazy as it sounds, crocodiles are known to swallow stones when they are on the banks of the water. The crocodile does this to not only help its digestive system but also to aid the crocodiles water buoyancy. It is thought that by swallowing stones, the crocodile may also be able to swim to deeper parts of the water.
Animal Planet - Crocodile with moving jaw