Of that giant ridge of bone making the sail shape on its back, the first four dorsal vertebrae are not known still, though the fifth already has a significantly large neural spine growing from the top of the back. This continues to the 17th dorsal vertebrae where the tall neural spine is longer than those of the sacral vertebrae (there are 6 over the hips) and then, after the hips and on toward the tail, the vertebrae again possess tall neural spines which gradually shorten down a short length of the tail. Ouranosaurus had a longer face than its cousin Iguanodon at 67 centimeters long. The average length of the skull of a horse is about 60 centimeters long, to put that in perspective. The skull of Ouranosaurus fitted 88 teeth, imagine a piano made of dinosaur teeth!, whereas that horse's head only manages about 44 teeth.