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Scientists say fossils showing ancient fins forerunners of arms, legs

This specimen of the fossil Tujiaaspis vividus from 436 million-year-old rocks was found in Hunan Province and Chongqing, China. Photo courtesy of Zhikun Gai
This specimen of the fossil Tujiaaspis vividus from 436 million-year-old rocks was found in Hunan Province and Chongqing, China. Photo courtesy of Zhikun Gai

Sept. 28 (UPI) -- Ancient fossils of a jawless freshwater fish appear to make a connection of the first sign of paired fins and the forerunner of arms and legs, researchers from China and Britain said in a new paper released Wednesday, according to the University of Bristol.

The study, led by Min Zhu, of the Institute of Vertebrate Palaeontology and Palaeoanthropology in Beijing, and Philip Donoghue, from the University of Bristol, analyzed the fossil found in rock dating some 436 years ago. The fossil was found in the Hunan Province of China.

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The fossil revealed for the first time that the mysterious galeaspids, a jawless freshwater fish, possessed paired fins. It shows the primitive condition of paired fins before they separated into pectoral and pelvic fins, which would eventually evolve into arms and legs.

"The anatomy of galeaspids has been something of a mystery since they were first discovered more than half a century ago," said the study's first author and Bristol alum Zhikun Gai in a statement.

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"Tens of thousands of fossils are known from China and Vietnam, but almost all of them are just heads. Nothing has been known about the rest of their bodies until now."

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Gai called the new fossils preserving the whole body of the galeaspid for the first time "spectacular."

He said they revealed "that these animals possessed paired fins that extended continuously, all the way from the back of the head to the very tip of the tail. This is a great surprise since galeaspids have been thought to lack paired fins altogether."

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Professor Donoghue said the discovery breathes new life into a century-old hypothesis for the evolution of paired fins.

"This 'fin-fold' hypothesis has been very popular, but it has lacked any supporting evidence until now," Donoghue said in a statement. "The discovery [of] Tujiaspis resurrects the fin-fold hypothesis and reconciles it with contemporary data on the genetic controls on the embryonic development of fins in living vertebrates."

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