CHANGSHA: More than 160 scholars and researchers from China, the United States, Canada, Russia and other countries have recently wrapped up joint field work and academic discussions on the Cambrian explosion and mass extinction in central China’s Hunan Province, according to the Chinese Academy of Sciences (CAS).
It was the first time Chinese and foreign experts had visited the Huayuan biota fossil site since research on it was published in January, as they sought clues to the Cambrian explosion and the mass extinction that followed. The site lies in Xiangxi Tujia and Miao Autonomous Prefecture in Hunan.
Concluding their work on Friday, the experts agreed that the Huayuan biota dates from just after the Sinsk mass extinction, fills a global gap in Cambrian Stage 4 soft-bodied fossil records, and is a valuable repository for studying the early evolution of life on Earth.
It falls chronologically between the peak of the Cambrian explosion, represented by the Chengjiang biota, and the later Burgess Shale, documenting marine life after the Sinsk mass extinction.
Over 500 million years ago, the Cambrian explosion gave rise to almost all animal phyla on Earth. It was followed by the Sinsk mass extinction, which wiped out countless early animals. Limited fossil evidence had long constrained scientists’ understanding of the catastrophe and how life had recovered afterward.
Research on the Huayuan biota, published in the journal Nature earlier this year, for the first time revealed the impact of this mass extinction on Earth’s biosphere.
Zhu Maoyan, a CAS academician and researcher at the Nanjing Institute of Geology and Palaeontology, located in east China, led the research endeavor. His team conducted five years of systematic excavations at the Renkupo section in Mozi Village, Huayuan County.
They collected more than 50,000 fossil specimens and identified 153 animal species, nearly six-tenths of them new, bringing to light a fossil trove that had lain buried for hundreds of millions of years.
Over 500 million years ago, the Xiangxi region was a deep-marine slope environment that provided exceptional conditions for preserving fine anatomical details.
Earlier studies relied largely on fossils of shallow-water shelly animals, leading researchers to infer that marine life became scarce after the Sinsk mass extinction, Zhu said. The abundant fossils of the Huayuan biota have amended that view and provided solid field evidence for deep-water refugia, he said.
Deep waters may have buffered the effects of the catastrophe, allowing some organisms to survive and preserving lineages for subsequent evolution, Zhu explained.
“This fossil site is very special. You can find fossils very quickly here,” said John Paterson, a professor at Australia’s University of New England, at the Renkupo section. “Here, fossils are abundant, and the diversity is remarkable.”
He said the site offered ample material for research, with many species belonging to previously unknown groups.
Representative taxa in the Huayuan biota closely match discoveries from the Burgess Shale in Canada. This particularly interested Jean-Bernard Caron, a researcher at Canada’s Royal Ontario Museum. After reading about the findings in Nature, he hoped to visit the excavation site and examine the evidence firsthand.
“I am excited to see this whole assemblage of fossils representing different groups of organisms. I have already seen many of these groups at fossil sites in the Burgess Shale in Canada,” Caron said.
He suggested that although these organisms inhabited widely separated seas during the Cambrian, they had originated earlier and could disperse between regions. Rather than individual animals swimming long distances, their larvae were more likely spread by ocean currents, he said. This process unfolded over immense spans of geological time and demonstrated that these organisms shared ancient common ancestors.
Douglas Erwin, an external professor at the Santa Fe Institute in the United States, said the fossils from the Huayuan biota were exquisitely preserved, retaining fine internal anatomical structures.
Their occurrence in deep-water facies deposited after the Sinsk mass extinction indicated that deep-water organisms had a better chance of surviving the catastrophe than shallow-water groups, he added.
Zhu said research on the Huayuan biota was only just beginning, with many unknown taxa in the collections still awaiting investigation.
The team will pursue multidisciplinary research to clarify the extent of the Sinsk mass extinction’s impact, investigate how deep-water refugia formed, and reconstruct changes in ancient marine ecosystems, Zhu added. –Agencies
