Ichthyosaurs (Greek for 'fish lizard' - ιχθυς meaning 'fish' and σαυÏος meaning 'lizard') were giant marine reptiles that resembled fish and dolphins. Ichthyosaurs lived during a large part of the Mesozoic era, having appeared about 250 million years ago (Mya), slightly earlier than the dinosaurs (230 Mya); and disappeared about 90 Mya, about 25 million years before the dinosaurs became extinct. During the middle Triassic Period, ichthyosaurs evolved from as-yet unidentified land reptiles that moved back into the water, in a development parallel to that of modern-day dolphins and whales.