The oldest ichthyosaurs -- of which we have found around 80 different species -- existed in the early Triassic, and the fossils we have found indicate an evolution from a land-dwelling reptile. Those earliest specimens exhibit lizard-like features -- necks, long tails, an absence of a dorsal fin, a slim body. As millions of years passed, they grew to resemble dolphins; yet what they originally evolved from is a mystery.
A new discovery made in China could help solve that mystery: the first ever fossil of an amphibious ichthyosaur, found by a team led by researchers at the University of California, Davis. This is the first time that paleontologists have found direct evidence that ichthyosaurs could come onto the land.
The specimen is dated back to the Triassic period, and is about 248 million years old. It measures just 45 centimetres (1.5 feet), and was equipped with unusually large, flexible flippers that would have allowed the animal to move about on land, probably humping along much like a seal.
It also had flexible wrists -- which it would need for crawling along the ground -- and a short snout, closer to those of land reptiles than the long snouts of aquatic ichthyosaurs. And its bones were thicker and heavier -- which fits with the hypothesis that marine reptiles developed heavier bones as they evolved from terrestrial animals in order to battle coastal surf to reach the deep sea.
The discovery could help us learn not just how ichthyosaurs evolved, but how animals might evolve in the future: the amphibian lived just four million years after the Permian-Triassic extinction event 252 million years ago.
"This was analogous to what might happen if the world gets warmer and warmer," said lead author and professor in the UC Davis Department of Earth and Planetary Sciences Ryosuke Motani. "How long did it take before the globe was good enough for predators like this to reappear? In that world, many things became extinct, but it started something new. These reptiles came out during this recovery."