Some diseases, which affect humans today, can be seen to have affected fossil vertebrates that lived over 150 million years ago. One such disease is arthritis, which causes the bone to breakdown and become very rough around the joints. This fossil bone, a femur (thigh bone) of a fossil crocodile called Metriorhynchus, can be seen to have been affected by arthritis at one end which would have made walking and swimming very painful for the animal. As well as diseases we also find evidence amongst fossils of animals that suffered broken bones that later healed.