Spinosaurus (Spinosaurus aegyptiacus) dinosaur, illustration. Spinosaurus was a large theropod dinosaur that lived 95 to 70 million years ago. It had a large sail along its back formed from very long neural spines. The sail was thought to act as a thermoregulator or sexual display. It's teeth and jaw shape indicates that it fed mainly on fish. It is thought that it was semi-aquatic. The largest specimen measured 18 metres in length making it the largest carnivorous dinosaur that ever lived.