GEOGRAPHY

Linyi Fauna 504 Million Years Ago: Exploring a New Window into Ancient Life


On April 15, China Science Daily learned from the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences (hereinafter referred to as the Institute of Ancient Sciences) that the Cambrian outbreak research team of the Institute of Ancient China found a cambrian specific buried fossil bank from North China, which is about 504 million years old, and named it “Linyi Fauna”. The results of the study were published online in the National Science Review on April 5.

“The discovery of this unique library of specific buried fossils provides a new window into the early radiation differentiation, migratory diffusion, community structure and bioquageography of animals following the Cambrian explosion.” Zhao Fangchen, the author of the paper and a researcher at the Institute of Ancient Studies, told China Science News.

Look for a library of specific buried fossils

The Cambrian explosion, which occurred around 530 million years ago, was an unprecedented rapid evolutionary event, with animals, including vertebrates, appearing rapidly in just a few million years, and representatives of most animal phylums appeared in the oceans in just 20 million years in the early Cambrian period, which has an important place in the entire history of the evolution of life on Earth.

Zhao Fangchen told China Science Daily that the problems related to the Cambrian explosion have always been the core of the research of the paleontological community, and the Cambrian specific buried fossil library, also known as the Burgess Shale Fossil Library, which is rich in exquisite multi-phylasoft body fossils, is the main window to understand this major biological evolution event.

Since the discovery of the famous Burgress Shale biota in Walcott in 1909, more than 20 Cambrian-specific buried fossil banks have been discovered around the world, especially the discovery of the Chengjiang Fauna, which opened the history of the South China Block as a related research hotspot, and new fossil banks are still emerging in recent years.

However, the temporal and spatial distribution of Cambrian-specific buried fossil banks is uneven, and most of the famous Cambrian-specific buried fossil repositories are concentrated in the South China Plate and lauren continent (the main body of the present-day North American continent).

“This geographical imbalance was most pronounced during the middle Cambrian period (Miaolingian), when most of the specific buried fossil repositories were located on the continent of Lauren, at a time when cambrian evolutionary fauna was at its most prosperous.” Zhao Fangchen said, “These objective conditions have greatly restricted our comprehensive understanding of the appearance and pattern of cambrian evolutionary fauna. ”

The North China Block was an independent continent during the Cambrian period with a unique tectonic evolutionary history. As the standard area of traditional Chinese “Middle Cambrianism”, the mid-Cambrian stratigraphic sequence here is complete and rich in fossils, which is a potential area for finding a specific buried fossil bank of this period.

35 fossil taxa were discovered

In recent years, the Cambrian outbreak research team of the Southern Paleo institute has carried out a lot of field work in North China, and selected representative strata and cross-sections for centralized collection, and collected thousands of exquisite fossil specimens.

Zhao Fangchen introduced that the Linyi fauna studied this time comes from the Sikou section in the western suburbs of Linyi City, Shandong Province, and the soft body fossils are concentrated in the black and yellow-green shale in the lower part of the Panchegou section of the Cambrian Zhangxia Formation.

Through the study of trilobite fossils, the researchers speculate that the age of the specific buried fossil bank was determined to be in the early Drumian period of the Cambrian Miaoling Period, about 504 million years ago, slightly later than the Burgess shale biota.

“At present, more than 35 fossil taxa have been found in the Linyi fauna, including at least 8 phyla and multiple ecological types, enriching the diversity of marine life and communities during this period.” Zhao Fangchen told China Science Daily that the most diverse taxa in the group are non-trilobite arthropods, and the most prominent are the radiodonts and mollisoniids. In addition to arthropods, diverse sponges and worm-like animals are also a major feature of the Linyi animal fossil group.

The researchers found that most of the fossils in the Linyi fauna were preserved in soft body form, and many of them preserved delicate anatomical structures, such as appendages, eyes, digestive systems and bristles, providing new information for further understanding the anatomy of these organisms. Like other classical Burgess shale-type specific buried fossil banks, the soft body structure in the Linyi special buried fossil library is preserved in the form of carbon film in the formation where the background layer interacts with the event layer, showing the universality of similar burial paths in soft body fossil preservation.

Since other specific buried fossil repositories of similar eras are concentrated on the lauren continent, and the paleo-geographical location of the North China Plate in the Cambrian Period has long been disputed, the discovery of the Linyi fauna provides a unique perspective for studying the biogeography of the middle Cambrian period.

A representative taxon in the Linyi fauna. A. Thexe spinosa; Symmetric Morrisonia symmetrica;C. Diagoniella diagonal sponge of the group;D. Don’s beguiser Thelxiope tangi sp. nov;E. Mouthparts of Cordaticaris striatus;F, Standard Changqingia puteata;G, Undetermined worm;H. The forebutment of cord-striped shrimp Cordaticaris striatus; The forepith of the monster-hugging insect. (Photo courtesy of Nangu)

Ecological restoration map of Linyi fauna (painted by Yang Dinghua and guided by Zhao Fangchen)

Photos of scientific expedition personnel working in the field in linyi area, from left to right, are Zeng Han, Tang Yonggang, Sun Zhixin, and Zhao Fangchen. (Photo courtesy of Nangu)

Hints act as biogeographic bonds

There are many identical biological types between the Linyi fauna and the North American-specific buried fossil pool of the same period, some of which are rare arthropods such as Thelxiope and Mollisonia. “It is very rare even in North America, where it originated, suggests a close connection between North China and the North American mollusk fauna during this period.” Zhao Fangchen said.

To this end, the Cambrian outbreak research team used quantitative analysis methods such as cluster analysis, non-metric multidimensional scale transformation and network analysis to support the connection between north China and north American mollusk fauna, and then showed that north China may act as a biogeographic link between East Gondwana and North America.

Zhao Fangchen also pointed out that due to the differences in paleogeographic evidence from different angles, the biogeographic interpretation of this connection needs further research and evaluation.

In the upper and lower shale sections of the Mantou Formation (Miaoling Shiwu period), which are older than the Linyi special buried fossil repository, the Cambrian outbreak research team also found well-preserved soft body fossils. The continuous distribution of such fossils in the middle Cambrian strata of the eastern North China Plate makes North China an important potential area for studying the succession of biological faces during this period.

Zhao Fangchen said that if the discovery of the Chengjiang fauna has opened the prelude to the study of a series of Cambrian specific buried fossil banks in the South China Plate, then the Linyi Fauna, as the first Cambrian specific buried fossil library in the North China Plate to be comprehensively studied, is also expected to open a new chapter in the study of the Cambrian Special Buried Fossil Library in North China. (Source: China Science Daily Shen Chunlei)

Related paper information:https://doi.org/10.1093/nsr/nwac069

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