A "new window" for exploring the Cambrian explosion! This fossil repository in Linyi is not simple!

The Cambrian Explosion Research Team of Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, discovered a Cambrian Explosion fossil reservoir about 504 million years old in North China, and named it "Linyi Fauna". The relevant research results were recently published online in National Science Review.

Zhao Fangchen, an author of the paper and a researcher at the Institute of Paleontology and Anthropology, said: "The discovery of this unique and exceptionally buried fossil reservoir provides a new window for a deeper understanding of the early radiation and differentiation, migration and diffusion, community structure and biopaleogeography of animals after the Cambrian Explosion."

Searching for unique buried fossil reservoirs

The Cambrian explosion that occurred around 530 million years ago was an unprecedented rapid evolutionary event. Animals, including vertebrates, appeared rapidly in just a few million years. Representatives of most animal phyla appeared in the ocean in just 20 million years in the early Cambrian period, which plays an important role in the entire history of the evolution of life on Earth.

Zhao Fangchen introduced that issues related to the Cambrian Explosion have always been the core of research in the paleontological community, and the Cambrian special burial fossil deposit, also known as the Burgess Shale-type fossil deposit, which is rich in exquisite soft-bodied fossils of various categories, is the main window for understanding this major biological evolution event.

Since Walker discovered the famous Burgess Shale biota in 1909, more than 20 Cambrian unique buried fossil deposits have been discovered around the world. In particular, the discovery of the Chengjiang fauna opened up the history of the South China Plate as a hot spot for related research, and new fossil deposits have continued to emerge in recent years.

However, the temporal and spatial distribution of Cambrian specific burial fossil deposits is not uniform. Most of the famous Cambrian specific burial fossil deposits are concentrated in the South China Plate and Laurentia (the main body of today's North American continent).

"This uneven geographical distribution was most obvious in the middle Cambrian period, when most of the exceptional fossil deposits were located in Laurentia, just as the Cambrian fauna was at its most prosperous," said Zhao Fangchen. "These objective conditions have largely restricted our comprehensive understanding of the appearance and pattern of the Cambrian fauna."

The North China Plate was an independent continent in the Cambrian period with a unique tectonic evolution history. As the standard area of ​​the traditional "Middle Cambrian" in China, the stratigraphic sequence of the Middle Cambrian here is complete and rich in fossils, making it a potential area for finding special buried fossil reservoirs of this period.

35 fossil groups discovered

In recent years, the Cambrian Explosion Research Team of the Nanjing Institute of Paleoanthropology and Anthropology has carried out a lot of field work in North China, and selected representative strata and sections for concentrated collection, collecting thousands of exquisite fossil specimens.

Zhao Fangchen introduced that the Linyi fauna studied in this study came from the Sikou section in the western suburbs of Linyi City, Shandong Province. The soft-bodied fossils were concentrated in the black and yellow-green shales in the lower part of the Panchegou section of the Zhangxia Formation of the Cambrian.

Through the study of trilobite fossils, researchers speculated that the age of the special buried fossil reservoir was determined to be in the early Gushanian period of the Miaolingian Period of the Cambrian Period, about 504 million years ago, slightly later than the Burgess Shale Biota.

"At present, more than 35 fossil groups 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 said that the most diverse group in the assemblage is non-trilobite arthropods, among which the most eye-catching are the Anomalocaris and Morrison worms. In addition to arthropods, a variety of sponges and worm-like animals are also a major feature of the Linyi animal fossils.

The researchers found that most of the fossils in the Linyi fauna are preserved in the form of soft bodies, and many of them preserve fine anatomical structures, such as appendages, eyes, digestive systems, and bristles, providing new information for further understanding of the anatomical structures of these organisms. Like other classic Burgess Shale-type special taphonomic fossil deposits, the soft-body structures in the Linyi special taphonomic fossil deposits are preserved in the form of carbon films in strata where background layers and event layers alternate, showing the prevalence of similar taphonomic pathways in the preservation of soft-body fossils.

Since other unique buried fossil deposits of similar age are concentrated in Laurentia, the paleogeographic location of the North China Plate in the Cambrian has long been controversial. The discovery of the Linyi fauna provides a unique perspective for studying the biogeography of the middle Cambrian.

Suggested to act as a biogeographical link

The Linyi fauna has many common biological types with the North American special burial fossils of the same period, including some rare arthropods, such as the Miyin worm and the Morrison worm. "Even in their native North America, they are very rare, which suggests that the soft-bodied fauna of North China and North America were closely connected during this period," said Zhao Fangchen.

To this end, the Cambrian Explosion research team used quantitative analysis methods such as cluster analysis, non-metric multidimensional scaling transformation and network analysis to support the connection between the soft-bodied fauna of North China and North America, and further indicated that North China may serve as a biogeographic link between East Gondwana and North America.

Zhao Fangchen also pointed out that since there are still differences in paleogeographic evidence from different angles, the biogeographic explanation of this connection still needs further research and evaluation.

In the upper and lower shale sections of the Mantou Formation (Miaolingian Wuliu Stage), which are older than the Linyi special buried fossil deposit, the Cambrian Explosion research team has also discovered well-preserved soft-bodied fossils. The continuous distribution of such fossils in the middle Cambrian strata in the eastern part of the North China Plate makes North China an important potential area for studying the evolution of biological features during this period.

Zhao Fangchen said that if the discovery of the Chengjiang fauna opened the prelude to a series of studies on Cambrian specific burial fossil deposits in the South China Block, then the Linyi fauna, as the first Cambrian specific burial fossil deposit to be comprehensively studied in the North China Block, is also expected to open a new chapter in the study of Cambrian specific burial fossil deposits in North China.