The Lesie fauna reveals the early appearance of the Ordovician biological radiation

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Ecological restoration map of the Liexi fauna (drawn by Sun Jie)

Recently, the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences (hereinafter referred to as the Nanjing Institute of Paleontology), together with the hunan museum and the cooperative team of Central South University, discovered the liexi fauna, a special buried fossil bank of the early Ordovician, in Yongshun, Hunan, revealing the marine ecological features of the early Ordovician biological radiation. On July 13, the results were published online in the Proceedings of the Royal Society B.

In the 1980s, evolutionary paleontologist Professor Sepkoski proposed the evolution curve of marine animal diversity since the global Phanerozoic, identified the three major marine evolutionary fauna of the Phanerozoic, and proposed the concept of Ordovician radiation for the first time. Entering the Ordovician, marine organisms began the process of “great radiation”, which was manifested in the outbreak of biological taxa at the level of “order”, “family” and “genus”, and the succession of some original biological groups.

Huang Diying, a researcher at the Nanjing Institute of Paleontology, introduced that the Ordovician biological radiation constructed the basic framework of the Paleozoic evolutionary fauna, and also enabled the Paleozoic fauna dominated by filter-feeding organisms and reef-building organisms to complete the comprehensive replacement of the Cambrian fauna dominated by arthropods.

Previous studies of Ordovician biological radiation have generally been based on “mineralized” specimens, while “unminalized” fossils have been less involved. The special buried fossil library can more completely reflect the appearance of marine life at that time, providing a window for a comprehensive understanding of the Ordovician sea world.

Huang Diying told China Science Daily: “Unlike many Cambrian specific buried fossil banks, so far, only a small number of Ordovician specific buried biota have been found worldwide, especially the early Ordovician. ”

The Liexi fauna found this time was produced in Liexi Township, Yongshun County, Hunan Province, and the fossils came from the calcareous mudstones in the upper part of the Lower Ordovician Sabre Formation. Based on the combination of tooth-shaped thorn and pencilstone organisms, the researchers judged that the fauna was 475 million years old in the early Ordovician Flo order, slightly later than the famous Fezouata biota in Morocco and the Afon Gam biota in Wales.

The libraries of early Ordovician-specific buried fossils reported by previous generations are concentrated in high Ordovician latitudes, such as the Fezouata biota near the ancient Antarctic, the Afon Gam fauna at 60°S paleo-latitudes, etc., and are often preserved in limited or hypoxic environments. The South China Plate, where the Liexi fauna is located, was generally considered to be located in the low latitudes near the equator in the early Ordovician period, and the western Hunan region was located on the edge of the Yangtze Terrace, which was a shallow open terrace environment.

At present, researchers have found 11 phylum first-class taxa in the Liexi fauna, arthropods, sponges, echinoderms, gills, spinyces, molluscs, brachiopods, bryopods, mosses, hemizoans and chordates. The Lesy Fauna preserves a variety of ecological niche taxa, including endobenth, benthic fixation, benthic wandering, swimming and floating, reflecting a complex and complete marine ecosystem.

Huang Diying said that the early Ordovician was a key period for studying the origin of Paleozoic fauna and the early mechanism of ordovician biological radiation. The Age of the Liesi Fauna is 5 to 10 million years before the main curtain of the Ordovician biological radiation, and the specific buried fossils preserved include both the Remains of the Cambrian taxa (such as paleohelums, Otto worms, bulbous trilobites, etc.), as well as a large number of Ordovician Neosensic taxa (mosses, polychaetes, etc.), and the complex fossil combination provides new evidence for the succession from the Cambrian fauna to the Paleozoic fauna, revealing the early appearance of the Ordovician biological radiation. (Source: China Science Daily Shen Chunlei)

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