19th century illustration showing an Ichtyosaurus apparently walking! Early palaeontologists thought that Ichthyosaurus laid eggs on land, but fossil evidence shows that in fact the females gave birth to live young. As such, they were well-adapted to life as fully pelagic organisms. Ichthyosaurus is a genus of ichthyosaurs from the late Triassic and early Jurassic. It is among the best known ichthyosaur genera, with the Order Ichthyosauria being named after it. Ichthyosaurus was the first complete fossil to be discovered in the early 19th century by Mary Anning in England.