Ichthyosaurs 101 | National Geographic

• [Narrator] While dinosaurs roamed the Earth and pterosaurs ruled the sky, sea monsters called ichthyosaurs dominated the world's oceans. Ichthyosaurs were ancient reptilian predators. They first appeared about 251 million years ago during the Triassic Period, 20 million years before dinosaurs came about. True to their name, which means fish lizards in Greek, the earliest ichthyosaurs looked much like lizards with fins.

Over the course of their 100 million year existence, their bodies transformed and became more akin to fish in shape. They had long narrow skulls and jaws that were lined with sharp teeth. These teeth were used to catch prey like fish and squid. Their eyes were the largest ever recorded of any animal, which helped them see through the dark waters of the deep ocean. In fact, one species had eyes that were over 10 inches wide.

Their bodies ranged in size. Some barely reached the length of two feet, while the longest specimen was about 85 feet long. They had paddle-like fins and a vertical tail which helped ichthyosaurs, despite their great size, zip through water at speeds of over 22 miles per hour. All together, these qualities put ichthyosaurs at the top of the marine food chain.

By the late Cretaceous Period, about 25 million years before an asteroid wiped out the dinosaurs, ichthyosaurs became extinct. Some scientists believe it may have been due to severe climate change. But the exact reason why these early sea monsters died out is still a mystery.