Ophthalmosaurus, one of a group of marine reptiles called ichthyosaurs, had a graceful 5 m long dolphin-shaped body. Its almost toothless jaw was adapted for catching squid and fish. It had the largest eyes of any vertebrate. Fossil evidence shows that a ring of bone, which would have given support against water pressure, surrounded its eyeballs. This suggests that it hunted in deep dark water.
