Fossils of bryozoans appeared 530 million years ago
The three-act Cambrian explosion hypothesis has new evidence
Reporter Lu Chengkuan
When did bryozoans originate? New evidence for the three-act Cambrian explosion hypothesis?
Researchers from Northwest University and other units have found that the moss originated in the early Cambrian explosion 530 million years ago, rather than the Ordovician period previously thought to be 480 million years ago. This discovery further supports the three-act Cambrian explosion hypothesis proposed by the team of Shu Degan, an academician of the Chinese Academy of Sciences, and reveals the evolutionary process of the Cambrian animal kingdom from basic animals to protozoans to post-mouth animals over a period of 40 million years, reflecting the continuity and periodicity of the Cambrian outbreak process. The results were published online in the journal Nature on October 27.
Bryozoan is a true body cavity animal with a tentacle crown, is a type of aquatic group of solid benthic animals, mostly marine, contiguous groups, showing dendritic, the shape resembles a bryophyte, so the name of bryozoan, also known as moss, is a typical "grassroots animal".
Bryozoans, along with brachiopods and brooms, are called tentacle crowns, belonging to the sub-boundary of proto-mouth animals, with horseshoe-shaped tentacle crown feeding structure, its digestive tract is U-shaped, and the anus is located outside the tentacle crown, so it is called external animals. The body of a bryozoan has a calcium, colloidal or chitinous worm chamber secreted by surface cells, which can be preserved as fossils, but soft body information is difficult to preserve.
About 540 million years ago to 518 million years ago, the early Cambrian period was a magical geological history period. At that time, there was a sudden explosion on Earth of early ancestral representation of almost all living animals, including vertebrates, including large predators and various exotic animal types.
However, "the very important animal phyla in geological history, the bryozoans, has lacked a solid fossil record in the Cambrian period, and their living types are small, group life, modular growth, and ecological complexity, so they are considered to be the product of ordovician radiation." Zhang Zhifei, the corresponding author of the paper and a professor in the Department of Geology of Northwest University, introduced.
Recently, Zhang Zhiliang, a doctoral student supervised by Professor Zhang Zhifei, found several millimeter-level micro-fossils in the clastic limestone of the Xi artemisia ping section of the Xiaoyang Section of the Xiaoyang Section of the Xiaoyang Section of xiaoyang town, BaXian County, Shaanxi Province, through acid etching treatment. The study found that these micromorphites are the earliest known fossils of bryozoans on Earth.
"This result pushes the geological history of bryozoans from pre-Ordovician to early Cambrian explosions, pushing forward the geological history of bryozoans by at least 50 million years." Zhang Zhifei said.
The researchers used scanning electron microscopy and X-ray tomography to analyze and found that the fossils appeared in a two-way thin plate-like network, and the two sides of the back were covered with epidermal cells secreting chitin worm chambers. The insect chamber lacks obvious mineralization, alternating 5 or 7 columns in longitudinal direction, the modular geometric features are clear and recognizable, the sides are symmetrical, and the overall shape is conical. Fossil studies have shown that the delicate geometric distribution patterns and strict hierarchical systems of the fauna on both sides originated 530 million years ago and are an important ecological innovation in the Cambrian explosion.
At the same time, through the maximum simplicity of 52 features, 18 taxa and 2 outer groups and Bayesian branch systematic analysis studies, the Cambrian bryozoans are the basal taxons of bryozoans, representing the most primitive ancestor types. In this regard, Zhang Zhifei explained: "This means that the modular growth of animals on both sides and the regular community distribution are much earlier than imagined, suggesting that modern bryozoans may have originated from social ancestor types rather than single-lived ancestors." ”
Zhang Zhifei said that the fossils found in the argillaceous limestone of the West Artemisia section of the Dengying Formation show that Cambrian bryozoans are similar to later genera 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 the mud shale.
"This discovery provides new evidence for the formation of animal trees on Earth and the Cambrian explosion of life, showing that the study of specific fossils does not fully reveal the historical process of life evolution in earth history, and also needs the constraints and supplements of other fossils, and the discovery of this fossil provides a new time frame for the origin and evolution of the archeology of the earth's post-animal phyla." Zhang Zhifei said.
【Editor: Chen Wentao】
Source: China News Network
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