A girl tastes a crayfish during a crayfish festival held in Xuyi county, East China's Jiangsu province, June 12, 2017.?[Photo/Xinhua]

Crayfish originated in China, not North America as commonly believed, according to a researcher at the Chinese Academy of Sciences.

Not that it matters much to the Chinese people for whom the fresh crustaceans are a favorite snack on summer nights－but it's nice to know.

Shen Yanbin at the Nanjing Institute of Geology and Paleontology said the oldest fossil crayfish found in China dates to 124 million years ago, while the oldest one found in North America can only be traced back 100 million years.

"By far it is the earliest fossil crayfish found in the world," said Shen, who has scrutinized and researched hundreds of fossil crayfish unearthed in Liaoning province, together with his colleagues.

"The ancient crayfish look like the modern ones, but they also have body parts that differ from each other, especially the shape and number of legs of the male."

After analyzing the imprint of weeds, fish and shells in the fossils, Shen concludes that the ancient crayfish in China lived in freshwater but not seawater.

Pieces of fossil crayfish were unearthed in western Liaoning in the early 20th century, he said. Many of them were sent to Japan because at the time Northeast China was occupied by Japanese troops.

To study the fossils, Shen and two crustacean experts from the United States, Rod Taylor and Frederick Schram, had to borrow them from a museum in Yokohama.

For years, Shen has searched for fossil crayfish in Liaoning. He has gone to remote areas, asked dealers for information and bought specimens from various people.

He keeps a fossil of a crayfish trying to catch a fish and another of a crayfish lying on its back. (Most fossil crayfish are on their bellies.)

"Why all the crayfish suddenly disappeared from China around 100 million years ago is a mystery," Shen said. "And the connection of ancient crayfish in China and North America is still to be found."

In the 1920s, Japan imported crayfish to feed bullfrogs, and later introduced the species to China's Yangtze River Delta.

The red crustacean has become a popular food across China. According to a report from China's Ministry of Agriculture in June, the output of crayfish last year reached 899,100 metric tons, making China the world's largest producer. Nearly 5 million people are involved in the industry.

Some Chinese experts disagree with Shen, insisting that crayfish in fact originated in North America. Fang Xingxing, a researcher at Nanjing Agricultural University, said direct evidence of evolution and more fossil crayfish need to be provided to prove that the species originated in China.

Guo Jun contributed to this story.