Ichthyosaurus (derived from Greek "ichtyos" meaning lizard and "saurus" meaning lizard) is a genus of marine reptiles that appeared during the Triassic, reached their peak during the Jurassic, and disappeared during the Cretaceous Period, about 95 million years ago.
Ichthyosaurus were able swimmers, with streamlined bodies fully adapted to life in the sea. Although better adapted to water than any other reptiles, they still needed to go periodically to the surface to breathe air.
Ichthyosaurus ranged in size from five to nine meters in length. They had long powerful jaws with sharp teeth, four crescent-shaped fins, a stabilizing dorsal fin, and a fish-like tail with two lobes. They breathed air with lungs through nostrils which were close to the eyes, near the top of the snout.
Ichthyosaurus gave birth to live young, instead of laying eggs, as all the other reptiles do. This is known because the fossilized bones of baby Ichtiosaurus have been found inside the abdomen of adult specimens.
Ichthyosaurus were carnivorous reptiles, eating fish, octopus, and other swimming animals. Their fossils have been found in North America, South America, and Europe.