After 12 spring and autumn periods, Chinese scientists have made a major breakthrough in the field of paleontological research - the discovery of the "Cambrian fossil treasure house".
Not long ago, Zhang Xingliang, Fu Dongjing and others from the early life and environmental innovation research team of Northwest University published their research results for the first time in the journal Science: the Discovery of the 518 million-year-old Cambrian specific buried soft body fossil library - Qingjiang Biota - was found in the Changyang area of Yichang, Hubei Province, China.
Qingjiang Fossil Reservoir work site. Courtesy of Northwestern University
"The Qingjiang biota is a shocking scientific discovery!" Internationally renowned paleontologist Allison C. Daley pointed out in a review entitled "Treasures of Cambrian Fossils" published in the same journal of Science: "Its fossil richness, diversity and fidelity are world-class, and its scientific value is huge. Follow-up research will hopefully fill gaps in our understanding of cambrian explosions and address a range of scientific questions about the origin and evolution of animal phyla. ”
The mystery of the Cambrian explosion of life has not been solved so far
The vast majority of animal phylums were born in less than 1% of Earth's history, which puzzled Darwin
The period between about 542 million years ago and 530 million years ago is considered by the scientific community to be the beginning of the Cambrian Period. In this more than 10 million years, the Cambrian strata suddenly appeared with numerous invertebrate fossils; In the early, more ancient strata, no obvious ancestral fossils have been found for a long time. This phenomenon is known as the Cambrian Explosion of Life, referred to as the Cambrian Explosion.
The Cambrian explosion has been called a major "unsolved case" in the field of natural science research, and the vast majority of animal phyla was born in less than 1% of the history of the earth, which once puzzled Darwin.
"To solve the mystery of the Cambrian explosion, in addition to scientific conjecture, it is necessary to discover the appropriate scientific observation window - the fossil library, in order to find reliable fossil evidence." Professor Zhang Xingliang said that the Burgess biota in Canada and the Chengjiang biota in Yunnan, China, which have been discovered since 1909, are the precious fossil libraries that scientists dream of.
The Burgess Shale Fossil Bank was first discovered in 1909 in the Burgess Shale of the Mid Cambrian period in the Canadian Rockies, hence the name. This library of fossils has long been a leader in paleontology and evolutionary biology research. Compared with the common hard fossil library that preserves vertebrate bones, the Burgess Shale Fossil Library can not only preserve soft body forms such as tissues and organs other than animal bones, but also soft-bodied organisms such as jellyfish and sea anemones. This provides an excellent fossil record for exploring the evolutionary patterns and intensities of Cambrian explosions and for constructing the basic structure of animal trees of life.
More than 100 years after the discovery of the Burgess Shale Fossil Reservoir, more than 50 such fossil repositories have been found around the world. However, according to the standards of the quality of fossil preservation and the diversity of fossil species, only the Burgess Shale biota in Canada and the Chengjiang biota discovered in 1984 have become "ideal top research destinations".
Among them, in the 35 years since the discovery of the Chengjiang biota, more than 280 species have been found in hundreds of thousands of fossil specimens, and the relevant research results have been published in three major scientific journals such as Nature, Science and the Proceedings of the American Academy of Sciences 28 times, becoming the only fossil world natural heritage in China.
Despite this, there is still a large cognitive gap in the Cambrian explosion, and there are still many unsolved mysteries in the origin and evolution of animal phyla. As a result, finding the next "ideal top research destination" has become a big dream for the international paleontology community.
Knocked out half a Limboli worm
A huge treasure of Cambrian fossils is gradually revealed
Limboli worm. Courtesy of Northwestern University
Yichang Changyang County is located in the mountainous area of southwest Hubei, located in the middle and lower reaches of the Yangtze River and Qingjiang River, with a wide distribution of Cambrian geological layers.
In the summer of 2007, the weather in Hubei was unusually hot. Zhang Xingliang led Fu Dongjing, Liu Wei, Dai Tao and other graduate students to the Changyang area for investigation.
"At that time, the target strata was the Shipai biota, which appeared slightly later and was younger than the Chengjiang biota." Fu Dongjing recalled, "As usual, everyone took out the geological hammer and knocked it. Soon, Teacher Zhang Xingliang found a half-worm fossil that was thumb-length- Lin Joli Worm. ”
Lincholi is a "shrimp"-like arthropod that is very representative of the Burgess shale fossil library. Immediately after, the expedition also found the Narrow worm in this location. In 1984, when Professor Hou Xianguang discovered the Chengjiang biota, the first fossil found was the Narrow worm.
In the following 12 years, the early life and environmental innovation research team at Northwestern University has long insisted on field excavations and indoor research, and a huge treasure trove of Cambrian fossils has gradually revealed its true face.
"Some people say that we are lucky, but in fact, in the more than ten years before the discovery of this Lin Jolly worm, Zhang Xingliang's search for this fossil group has traveled all over the world." Luck always falls on people with hearts, doesn't it? Fu Dongjing said.
The research team named this fossil treasure the Qingjiang biota, in part because the fossils were buried at the confluence of the Qingjiang and Danjiang rivers. More importantly, the research team hopes that the Qingjiang and Chengjiang biota will become the world-renowned "China Liangjiang Biota" in the future.
The results of the study are getting more and more exciting
The preliminary study found 109 genera, 53% of which are entirely new genera that have never been recorded before
Simulation of qingjiang biota. Courtesy of Northwestern University
Even if the Linjoli worm and the Narrow worm are found, there are still many potential fossil production areas in South China and North China that need to be studied. "At the beginning, we still toured the whole year, going to Qingjiang about two or three times a year, waiting for the villagers to tell us that the water level was down and the riverbed was exposed, we hurried to go, and the snow was no exception." It was not until 2014 that the huge potential of this fossil pool was gradually confirmed, and the focus of research was completely shifted. Fu Dongjing said.
No less than fishing for needles on the seabed, Zhang Xingliang, Fu Dongjing and the team's master's and doctoral degrees have found more than 20,000 "bugs" in the "sea" 500 million years ago. "The workers used the crowbar to pry out a stone the size of 1 cubic meter, and we used a geological hammer to split along the shale level, while splitting and watching, and when we found the bugs, we sorted, numbered, packed, carried out of the mountain, and brought back to the laboratory." Then clean up each piece, discuss, identify, classify, and record. "Every fossil has a story, and every story about them is well known to us." ”
Every time a Cambrian fossil is found, researchers need to consult a lot of information. The results of the study are becoming more and more exciting, and of the 4351 fossil specimens that have been studied, 109 genera have been preliminarily identified, of which 53% are completely new genera species that have never been recorded before!
The biostatistical "sparsity curve" analysis shows that the species diversity of the Qingjiang biota is expected to exceed the global known library of Cambrian soft body fossils, including the Burgess Shale and Chengjiang.
According to reports, there are a total of 38 phylums in the animal kingdom on the earth today, and in the fossils of the Cambrian explosion of life, 20 living animal phyla and 6 extinct animal phyla have been found, but there are still 18 living animal phylums that have not yet found fossil representation in the Cambrian period. Over the past 35 years, paleontologists have found the earliest fossil records of many animal phylums in the study of the Chengjiang biota.
On the wall of the team's studio near the Danjiang River in Changyang hangs a photo of the team enlarged with a microscope, which is the ocean world 518 million years ago in the minds of scientists. Some of these ancient creatures are like jellyfish, sea shrimp, worms, some like watermelons, flowers... Some even have textures of the antennae and abdomen clearly visible and come to life.
Zhang Xingliang said excitedly: "At present, 85% of the genus of epizoans do not have mineralized bones, and the vast majority are jellyfish, anemones and other animals without bones. It is rare to be able to excavate so many fossils of soft bodies intact. ”
He explained that the "ultra-high fidelity" of these fossils is due to the fact that the fossils of the Qingjiang biota are mainly preserved in the form of native carbonaceous films, without obvious diagenesis and weathering.
This is just the tip of the iceberg
More unknown mysteries from 518 million years ago are waiting for scientists to explore
New species discovered in the Qingjiang biota. Courtesy of Northwestern University
The Qingjiang biota is 1050 km away from the Chengjiang biota. Zhang Xingliang told us: "Biostratigraphic studies have shown that the Qingjiang biota and the Chengjiang biota are contemporaneous biota located in different paleogeopauses. Both date back about 518 million years, at the height of the emergence of animal phyla during the Cambrian explosion of life. The scientific research value of the two is highly complementary. ”
Zhang Xingliang believes that compared with the Chengjiang biota, the Qingjiang biota lives in a deeper water environment far from the coast, representing a new biome in different ecological environments, which can be confirmed by more than half of its new genera species. Therefore, the subsequent large-scale excavation of the Qingjiang biota will provide first-hand materials for the discovery and exploration of new body configurations and new animal phyla, and will further improve our scientific understanding of the Cambrian explosion.
Previously, the early life and environmental innovation research team of the Department of Geology of Northwest University, led by Shu Degan, an academician of the Chinese Academy of Sciences, based on Darwin's conjecture of the "tree-shaped evolution" of life on earth, through decades of research and empirical evidence, outlined the basic outline of the three major branch evolution "big trees" of basic animals, proto-mouth animals and posterior-mouthed animals during the Cambrian life explosion, and then constructed a complete tree framework map of early animal lineage for the first time in the world.
"Through the research we have carried out, we have found that animals with bitensocular radiation symmetry dominate the Qingjiang biota, the body configuration of spiny cells is highly differentiated, and the extremely rare mosses in the molting animal taxa are flourishing. In addition, we have discovered many new species with strange shapes. As research unfolds, the Qingjiang biota will find more direct evidence of biological evolution for where the 'early animal lineage trees' forked and where they branched and scattered. Fu Dongjing said.
The fossils of the Qingjiang biota can be preserved in the form of native carbonaceous films, which is also an ideal material for burial and geochemical research, and then for in-depth paleoenvironmental research.
According to reports, the study of animal phylogenetic development, nutritional dynamics and the emergence of key evolutionary characteristics depends on the discovery of more soft structures and better morphological preservation, such as internal organs, gills, chords, neural tissue, cardiovascular system and so on. However, these are buried on highly unstable tissues and organs. What is the special burial mechanism that enables the Burgess Shale Fossil Bank to preserve the soft structure? This is also a problem that needs to be solved in the future research of the Qingjiang biota.
Zhang Xingliang's team believes that the two most fidelity Burgess shale fossil banks in the world, the Burgess Shale Biota and the Chengjiang Biota, have undergone serious geological modifications such as high temperature metamorphism and weathering after burial, and their samples have been unable to be used for in-depth burial research. The soft body fossils found in the Qingjiang biota miraculously preserved the original organic matter in the form of a native carbonaceous film.
"There is no doubt that this place will provide ideal material for the development of burial and geochemical research, and then for in-depth paleoenvironmental research." The problem of special burial mechanism of animal soft body structure that has plagued the academic community for many years may be cracked in the Qingjiang biota. Zhang Xingliang said.
"The Qingjiang biota research work has only just begun, and we have only opened the tip of the iceberg, and preliminary reports describe the fossil combination of the biota. Paleontological taxonomy and genealogical analysis will solve the problem of the origin and evolution of animal phyla. The study of sedimentology, burial, and geochemistry will solve the problems of why fossils are so well preserved and what the environmental conditions are. It may take decades, or even generations, of research to follow. Zhang Xingliang said.