Ichthyosaurus (derived from Greek ιχθυς meaning 'fish' and σαυρος meaning 'lizard') is an extinct genus of reptile, belonging to the aquatic ichthyosaur order, which was named after it. It is among the best known ichthyosaur genera.


Ichthyosaurus was smaller than most of its relatives, measuring 2 m (6 ft 8 inches) in length. Hundreds of incredibly well-preserved, fossilised skeletons have been found in Jurassic rock at Holzmaden, Germany. Some of the bones were still articulated. Some fossils still had baby specimens inside them, indicating that Ichthyosaurus (and other ichthyosaurs) were viviparous. Similar finds in the related Stenopterygius also show this. The German fossils also featured the outline of Ichthyosaurus's skin, revealing that it had a fleshy dorsal fin on its back and a large caudal fin. Other ichthyosaur fossils showed this feature was not limited to Ichthyosaurus.Ichthyosaurus's ear bones were solid, probably transferring water vibrations to the inner ear. Still, hunting by sight was the creature's main feeding activity; it had huge, sensitive eyes, protected by bony shields. Coprolites of Ichthyosaurus reveal that its diet consisted of fish and squid.It was initially believed that Ichthyosaurus laid eggs on land, but recent fossil evidence shows that in fact the females gave birth to live young. The babies were born tail first to prevent them from drowning in the water.