What kind of animal was an ichthyosaur?

An ichthyosaur was any member of an extinct group of aquatic reptiles, most of which were very similar to porpoises in appearance and habits. These distant relatives of lizards and snakes were the most highly specialized aquatic reptiles, but ichthyosaurs were not dinosaurs.

Ichthyosaurs had a very wide geographic distribution, and their fossil remains span almost the entire Mesozoic Era (251 million to 65.5 million years ago); but they were most abundant and diverse during the Triassic and Jurassic periods (251 million to 145.5 million years ago).

'Ichthyosaurus', a representative genus from which the larger group takes its name, was about 3 metres (10 feet) long and was probably able to move through the water at high speeds. Very fishlike in appearance, it is especially well known from Early Jurassic deposits in England.