Scientists have discovered the fossil of an amphibious ichthyosaur, a dolphin-like marine reptile that lived during the Triassic period.
The 1.5 foot long fossil is about 248 million years old. Researchers found it in China’s Anhui Province.
Until now, there were no fossils marking their transition from land to sea.
“But now we have this fossil showing the transition,” says lead author Ryosuke Motani, professor of Earth and planetary sciences at University of California, Davis. “There’s nothing that prevents it from coming onto land.”
Unlike ichthyosaurs that were fully adapted to life at sea, this one had unusually large, flexible flippers that likely allowed for seal-like movement on land.
It had flexible wrists, essential for crawling on the ground. Most have long, beak-like snouts, but the amphibious fossil has a nose as short as that of land reptiles.
The body also contains thicker bones than previously described ichthyosaurs. Most marine reptiles who transitioned from land first became heavier, for example with thicker bones, in order to swim through rough coastal waves before entering the deep sea.
A warmer world
The study, published in the journal Nature, has implications that go beyond evolutionary theory, Motani says. The animal lived about 4 million years after the worst mass extinction in Earth’s history, 252 million years ago.
Scientists have wondered how long it took for animals and plants to recover after such destruction, particularly since the extinction was associated with global warming.
“This was analogous to what might happen if the world gets warmer and warmer,” Motani says. “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.”
Researchers from Peking University, Anhui Geological Museum, Chinese Academy of Science, University of Milan, and the Field Museum in Chicago contributed.
The National Geographic Society, National Natural Science Foundation of China, Nanjing Institute of Geology and Palaeontology, Research Fund for the Doctoral Program of Higher Education, and the Department of Land and Resource of Anhui Province funded the research.
Source: University of California, Davis