Rulers of the Jurassic Seas; Prehistoric Beasts; Exclusive Online Issues; by Ryosuke Motani; 8 Page(s)

Picture a late autumn evening some 160 million years ago, during the Jurassic time period, when dinosaurs inhabited the continents. The setting sun hardly penetrates the shimmering surface of a vast bluegreen ocean, where a shadow glides silently among the dark crags of a submerged volcanic ridge. When the animal comes up for a gulp of evening air, it calls to mind a small whale--but it cannot be. The first whale will not evolve for another 100 million years. The shadow turns suddenly and now stretches more than twice the height of a human being.That realization becomes particularly chilling when its long, tooth-filled snout tears through a school of squidlike creatures.

The remarkable animal is Ophthalmosaurus, one of more than 80 species now known to have constituted a group of sea monsters called the ichthyosaurs, or fish-lizards. The smallest of these animals was no longer than a human arm; the largest exceeded 15 meters. Ophthalmosaurus fell into the medium-size group and was by no means the most aggressive of the lot. Its company would have been considerably more pleasant than that of a ferocious Temnodontosaurus, or "cutting-tooth lizard," which sometimes dined on large vertebrates.