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Fossil
remains show the first amphibious ichthyosaur found in China by a team led by a
UC
Davis scientist. Its amphibious characteristics include large flippers and
flexible wrists, essential
for crawling on the ground. Photo Credit: Ryosuke
Motani/UC Davis
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The
first fossil of an amphibious ichthyosaur has been discovered in China by a
team led by researchers at the University of California, Davis. The discovery
is the first to link the dolphin-like ichthyosaur to its terrestrial ancestors,
filling a gap in the fossil record. The fossil is described in a paper
published in advance online Nov. 5 in the journal Nature.
The
fossil represents a missing stage in the evolution of ichthyosaurs, marine
reptiles from the Age of Dinosaurs about 250 million years ago. Until now,
there were no fossils marking their transition from land to sea.
"But
now we have this fossil showing the transition," said lead author Ryosuke
Motani, a professor in the UC Davis Department of Earth and Planetary Sciences.
"There's nothing that prevents it from coming onto land."
Motani
and his colleagues discovered the fossil in China's Anhui Province. About 248
million years old, it is from the Triassic period and measures roughly 1.5 feet
long.
Unlike
ichthyosaurs 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, which are essential for crawling on the ground. Most
ichthyosaurs have long, beak-like snouts, but the amphibious fossil shows a
nose as short as that of land reptiles.
Its
body also contains thicker bones than previously-described ichthyosaurs. This
is in keeping with the idea that 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.
The
study's implications go beyond evolutionary theory, Motani said. This 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 said. "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."
Citation
Motani
R., Jiang D-Y, Chen G-B, Tintori A, Rieppel O, Ji C, Huang J-D. 2014. A
basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature,
2014; DOI: 10.1038/nature13866