Stock Photo - Spinosaurus (Spinosaurus aegyptiacus), artwork. Spinosaurus was a large theropod dinosaur that lived 155 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. The largest specimen measured 18 metres in length making it the largest carnivorous dinosaur that ever lived.