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About Ophthalmosaurus:
Looking a bit like a foreshortened, bug-eyed dolphin, Ophthalmosaurus wasn't technically a dinosaur, but an ichthyosaur--an ocean-dwelling lizard that differed in certain anatomical respects from land-dwelling dinosaurs.
As you can guess from its name, what set Ophthalmosaurus apart from other ichthyosaurs were its eyes, which were hugely oversized (about four inches in diameter) compared to the rest of its body. As with other aquatic reptiles, these eyes were encircled by bony structures called "sclerotic rings," which allowed the eyeballs to maintain their spherical shape in conditions of extreme water pressure.
Why did Ophthalmosaurus evolve such gigantic eyes? No one knows for sure, but it's possible that this adaptation helped it to locate prey at great depths (where a creature's eyes have to be as efficient as possible to gather in the increasingly scarce light).
