Crocodiles are one of the oldest living creatures on the planet, believed to be around 200 million years old, meaning that crocodiles existed back in the time of the dinosaurs. As crazy as it sounds, crocodiles have been known to swallow rocks when they are on the edge of water. The crocodile does this not only to aid its digestive system, but also to help the crocodiles’ buoyancy in the water. It is thought that swallowing rocks also allows the crocodile to swim to deeper parts of the water.