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Fossil Trove
Paleobiologists find extraordinarily preserved fossils that will help understand the Cambrian Explosion
By Wang Hairong  ·  2019-06-10  ·   Source: NO.24 JUNE 13, 2019

Researchers from the Department of Geology, Northwest University, collect fossils on the bank of the Danshui River in central China's Hubei Province in 2018 (COURTESY PHOTO)

In a valley near Changyang County of central China's Hubei Province, a small creek named Danshui River converges with the Qingjiang River at Jinyangkou Town. Innumerous pieces of layered gray claystone are strewn over the Danshui's bed and banks at its junction with the Qingjiang.

For Zhang Xingliang, a professor at Northwest University in Xi'an, capital city of Shaanxi Province, the rocks hold keys to unraveling the mystery shrouding the Cambrian Period that extended from about 541 to 485 million years ago, known for an eruptive appearance of animal life.

Zhang and his team members have uncovered a fossil Lagerstätte, a fossil-rich rock deposit featuring Cambrian Period creatures, which they named Qingjiang biota. The fossil locality is situated near the junction of the Qingjiang and its tributary Danshui, and on the bank of the Danshui.

So far, more than 20,000 pieces of fossil specimens have been collected there. "A total of 4,351 fossil specimens have been analyzed, 109 taxa have been identified, of which 53 percent are new," said Fu Dongjing, a young paleontologist at Northwest University.

This discovery was published in world-renowned Science magazine in March, with Fu being the first author and Zhang a co-author.

Preliminary taxonomic analyses suggest its diversity could rival that of the Chengjiang and Burgess Shale biotas in the future, Zhang said. The two famous biotas found in China and Canada shed light on the evolution of Cambrian ecosystems.

"The fossils are a scientific legacy of humankind, and it will take generations of people to decipher them," Zhang told Beijing Review. He said that the team will continue to analyze the remaining specimens, study the paleo-environment, and answer questions such as how these creatures were preserved so well in fossil forms.

Researchers in Northwest University analyze a fossil (COURTESY PHOTO)

A significant discovery

The first fossil specimen of the Qingjiang biota was discovered in the summer of 2007 when Zhang and his graduate students at Northwest University were doing field studies in the area.

In order to explore the area, over the past 12 years, whenever the river's water level dropped, exposing underwater rocks, the research team collected fossils, which is a painstaking job.

Workers were hired to pry out rocks, usually 1 cubic meter in size, with pry bars. Then scientists split the shales along the layers with geological hammers, scrutinizing the rock to detect fossils, which were classified, numbered, packed, and shipped out of the mountains to be analyzed, Fu said.

In the laboratory, a specimen was prepared under a microscope first, then scanned by electron microscopy to identify the fossil's ultrastructure and elemental composition, and later scanned by a high-precision three-dimensional scanner for further analysis.

To identify the creatures living 518 million years ago, researchers spent a lot of time reading literature, Fu said. As they identified more and more new genera and species, they gradually realized the value of the fossil Lagerstätte.

"The merits of the Qingjiang biota mainly lie in the high proportion of new taxa, the highest relative diversity, the large number of soft-bodied fauna, and the high fidelity of fossil morphology," Fu said, adding that the biota promises great research potential.

Some 85 percent of the fauna in Qingjiang biota are soft-bodied, such as jellyfish and sea anemones, Zhang said. The soft-bodied fossils are remarkably preserved, showing not only exterior shapes but also internal organs.

The researchers "revealed a stunning new locality," wrote Allison Daley, a paleontologist at the University of Lausanne in Switzerland, in her article published in Science. "The fossils from the site fill gaps in our knowledge and raise questions about the earliest animal ecosystems," she added.

The Cambrian Explosion, a sudden appearance of many animal phyla in the early Cambrian Period, has been intriguing. In a geologically short interval, almost all major groups of animals had made their first appearances.

Many mysteries shrouding the period have been unraveled by fossils, while many questions are yet to be answered.

In the past century, more than 50 fossil Lagerstättes verifying the Cambrian Explosion have been discovered worldwide. The most celebrated one is the Burgess Shale in British Columbia in Canada, discovered in 1909. According to scientists, the Burgess Shale contains animals that lived 505 million years ago, many with bizarre anatomical features, bearing only the sketchiest resemblance to known animals. This indicates that life forms at the time were much more diverse than today, with a great majority of taxa going extinct later.

In 1984, Chinese paleontologist Hou Xianguang discovered a Naraoia fossil at the Chengjiang area in southwest China's Yunnan Province, leading to the discovery of the Chengjiang biota. In 2012, the fossil site was added to UNESCO's list of world natural heritage sites since it "presents fossil remains of the highest quality of preservation and conveys a complete record of an early Cambrian marine community."

According to scientists, in the 35 years since its discovery, more than 100,000 specimens have been collected in the Chengjiang area and over 280 taxa have been identified.

The Qingjiang and Chengjiang biotas, lying about 1,050 km apart and dating back about 518 million years to the peak of the eruptive appearances of animal phyla, are highly complementary in value, said Zhang.

"Further large-scale excavation of the Qingjiang biota will provide first-hand materials for the discovery and exploration of new body plans and new animal categories," Zhang said.

A hardworking team

The discovery of the Qingjiang fossil site would not have been possible without the persistent efforts of the early life research team at Northwest University over the past decades.

The team is led by Zhang's mentor, 73-year-old Shu Degan, an academician of the Chinese Academy of Sciences. Currently, 82 percent of the team's 33 members are under 35.

In the decades before 2007, team members traveled to many places at home and abroad to look for fossils, and after that, spent another decade collecting and analyzing specimens. In addition to discovering Qingjiang biota, they have other paleontological findings.

At the age of 50, Zhang has published more than 120 papers in academic journals at home and abroad, and won several national-level awards.

Shu and his assistants first published their findings in a paper in the academic journal Nature in 1996, and so far the team has published 14 papers in Nature and Science, and has twice won the National Natural Science Award, one of the most prestigious science awards in China. The team members' findings made the cover of Nature in February 2011 and January 2017.

One of the most significant discoveries is the Myllokunmingia, or Kunming fish, known to be the earliest vertebrate found on earth, discovered by Shu and his student Zhang.

In recent years, younger members of the team have published several significant findings.

Team member Han Jian, co-authored an article with Simon Conway Morris, a paleobiologist at the University of Cambridge, and other researchers about the newly discovered fossils of a tiny sea creature that is dubbed humans' earliest known ancestor. The article made the cover of the January 30, 2017 issue of Nature.

Through their persistent efforts, researchers at Northwest University have contributed to our understanding of the roots and shoots of the evolutionary tree, promising more findings from their most recent discoveries.

Copyedited by Rebeca Toledo

Comments to wanghairong@bjreview.com

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