Its snout is dotted with small pits that may have been the site of glands to help it detect changes in water pressure made by prospective prey. And on its head is a hole that would have housed a parietal, or third, eye. Lizards, frogs and some fish alive today have one of these. It’s light-sensitive and might have helped in locating other animals, especially when the pliosaur was surfacing from deep, murky waters.