~250 million years ago (Triassic)Reputable sourceWell documented
Ichthyosaurs Return to the Sea
On the timeline · around ~250 million years ago (Triassic) · The Triassic
What happened
As life recovered from the Great Dying, some reptiles returned to the water. Ichthyosaurs — sleek, dolphin-shaped 'sea dragons' — became fast marine predators; smaller ichthyosaurs survived until around 90 million years ago.
Why it matters
Among the first large reptiles to fully adapt to ocean life, ichthyosaurs even gave birth to live young at sea. Their fossils were among those that first led scientists to accept that species could go extinct.