Crocodiles are one of the planet's oldest living creatures, believed to be around 200 million years old, meaning crocodiles existed way back to the time of dinosaurs. As crazy as it sounds, crocodiles have been known to swallow rocks when they are at the banks of the water. The crocodile does this not only to help its digestive system, but also to promote the buoyancy of the crocodiles' water. It is thought that the crocodile can also swim to deeper parts of the water by swallowing stones.