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Tuesday, October 19, 2021

UC Davis researchers discover fossils that fill missing evolutionary gap

On Nov. 5, UC Davis released that a team led by campus researchers discovered the first fossil of an amphibious ichthyosaur that fills a missing part of the dinosaurs’ evolutionary period.

The fossil represents the transition from land to sea in the evolutionary history of ichthyosaurs, marine reptiles from the Age of Dinosaurs.

“Ichthyosaurs are fish-shaped externally but their skeletons are reptilian, suggesting that they descended from four-legged land reptiles and evolved into a fish-shape over time,” said team member and Professor Ryosuke Motani from the department of earth and planetary sciences. “However, no fossil was known to represent this transition from land to sea.”

Between 2010 and 2012, the team, consisting of scientists from UC Davis, Peking University, Anhui Geological Museum, Chinese Academy of Science, University of Milan and The Field Museum in Chicago, led multi-year excavations in Chaohu City, Anhui Province of China.

The fossil was discovered in 2011, and almost two years were spent in the lab studying and analyzing the fossil before the team noticed significant differences in the structure of this animal. According to a paper published by the research team in the scientific journal Nature, the ichthyosaur fossil had unusually large, flexible flippers and a short snout that allowed for movement on both land and sea. The body of the ichthyosaur also contained thick bones, an indication of an animal requiring a heavy bone skeleton to combat rough sea waves.

According to Motani, this transitional animal will allow scientists to scrutinize the timing of marine invasion.

“The important question here is if the invasion was related to the global warming that seems to have preceded the invasion,” Motani said.

According to co-author and team member Da-Yong Jiang from the department of geology at Peking University, the causes driving marine invasion could be multiple, including predation pressure and competition for food that may be lower in the sea than on adjacent land

Future studies will be conducted to determine if any other climatic or geographic factors affected the transition.

“We did not realize the importance of the specimen until much later.” said Motani. “It took about two years to fully appreciate what it was. Then, I was finally really excited, and the same goes for my colleagues.”

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