There is new evidence for the three act Cambrian explosion hypothesis
2021-10-28
When did bryozoans originate? New evidence for the three act Cambrian outbreak hypothesis? Researchers from Northwestern University and other units found that bryozoans originated in the Early Cambrian explosion 530 million years ago, rather than the Ordovician 480 million years ago. This discovery further supports the three act Cambrian outbreak hypothesis proposed by Shu degan, academician of the Chinese Academy of Sciences, and reveals the evolutionary process of the Cambrian animal kingdom from basic animals to protostomata and then to hindstomata in 40 million years, reflecting the continuity and periodicity of the Cambrian outbreak process. Relevant research results were published online in the journal Nature on October 27. Bryozoan is a eucoeloma with tentacle crown. It is a kind of fixed benthos in aquatic groups. Most of them are marine, living together in groups, showing a dendritic shape and similar to bryophytes. Therefore, it is called bryozoan, also known as bryozoan. It is a typical "grass-roots animal". Bryozoans, brachiopods and broomworms are called tentacle crown animals. They belong to the protostoma subfield. They have a horseshoe shaped tentacle crown feeding structure. Their digestive tract presents a U-shape, and the anus is located outside the tentacle crown, so they are called external anal animals. There are calcium, colloid or chitin chambers secreted by surface cells outside the body of bryozoans, which can be preserved as fossils, but the soft body information is difficult to preserve. The Early Cambrian, about 540 million to 518 million years ago, is a magical geological historical period. At that time, the early ancestors of almost all living animals, including vertebrates, suddenly appeared on the earth, including large predators and various strange animal types. However, "Bryozoa, a very important animal category in the geological history, has been lack of conclusive fossil records in the Cambrian. Their living types are small, group life, modular growth and complex ecology, so they are considered to be the product of the Ordovician radiation." Zhang Zhifei, corresponding author of the paper and professor of the Department of geology of Northwestern University, introduced. Recently, Zhang Zhiliang, a doctoral student under the guidance of Professor Zhang Zhifei, found several millimeter sized microfossils in the clastic limestone of xihaoping section of Dengying Formation, Xiaoyang section, Xiaoyang Town, Zhenba County, southern Shaanxi Province through acid etching treatment. The study found that these microfossils are the earliest known bryozoan fossils on earth. "This result pushed the geological history of bryozoans from pre Ordovician to Early Cambrian outbreak, and pushed the geological history of bryozoans forward by at least 50 million years," Zhang Zhifei said. Using scanning electron microscopy and X-ray tomography, the researchers found that these fossils showed a two-way thin plate-like network, with epidermal cells secreting chitin chambers on back-to-back sides. The insect chamber is lack of obvious mineralization. It is arranged alternately in 5 or 7 columns in the longitudinal direction. The modular geometric features are clear and distinguishable, symmetrical on both sides, and the overall shape is conical. Fossil studies show that the exquisite geometric distribution pattern and strict hierarchy of animal communities on both sides originated 530 million years ago, which is an important ecological innovation of the Cambrian outbreak. At the same time, the maximum parsimony method and Bayesian cladistics analysis of 52 characteristics, 18 groups and 2 exogroups show that Cambrian bryozoans are the backbone group of bryozoans, representing the most primitive ancestor type. In this regard, Zhang Zhifei explained: "this means that the modular growth and regular community distribution of animals on both sides are much earlier than expected. It is proposed that modern bryozoans may have originated from social ancestors rather than single living ancestors." Zhang Zhifei said that the fossils found in the argillaceous limestone of xihaoping section of Dengying Formation show that the Cambrian bryozoans are similar to the later genera and species and are suitable for living in a clear hard bottom environment, thus revealing the reason for the lack of bryozoan fossils in the specific fossil library preserved in shale. "This discovery provides new evidence for the formation of the earth's animal tree and the great outbreak of Cambrian life, indicating that the study of specific fossils can not fully reveal the historical process of life evolution in geological history, and it also needs the constraints and supplements of other fossils. The discovery of this fossil provides a new time frame for the origin and evolution of post vivid species on the earth," Zhang Zhifei said. (Xinhua News Agency)
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