The Cambrian fossils of the Chengjiang River in Yunnan have unveiled the mystery of the origin of ctenophores

The difficult fossil research team of Professor Hou Xianguang of Yunnan Provincial Key Laboratory of Paleontology Research of Yunnan University confirmed that the difficult fossils of this kind of benthic solidification were the stem groups of living ctenophores and jellyfish through systematic research on the difficult fossils of chengjiang biota , and constructed the evolution path of the basic body size of ctenophores. This discovery confirms the fact that ctenophores and australis co-originate from benthic solid ancestors, and solves the mystery of the origin of ctenophores phylum. The research results were published online in the form of a long article in march 21 in contemporary biology, a sub-journal of the American "Cell" publishing group, and will be officially published as a cover article on April 1.

Comparison between the Three-Dome Dai Flowerworm and the Wonderful Cupworm: A and B are the Top View Specimens (Pattern Specimens) and Interpretation Diagrams of the Three-Dome Dai Flowerworm; C is the SideView Specimen of the Three-Dome Dai Flowerworm; and D is the SideView Specimen of the Three-Domed Dai Flowerworm; and D is the SideView Specimen of the Three-Domed Dai Flowerworm. Profile picture

According to Professor Hou Xianguang's team, ctenophores are a type of bitenost animal, which is collectively referred to in traditional textbooks as coelenterates with another type of bitenost animals, such as spiny animals (corals, jellyfish, sea anemones, etc.), and it is believed that they are transitional types between sponge animals and triodermal animals (symmetrical animals on both sides). However, recent molecular systematics studies have shown that ctenophores may be basal taxa of multicellular animals, suggesting that the morphological characteristics they share with echinozoa may be the result of convergent evolution. Therefore, the origin and early evolution of ctenophores have become one of the major scientific problems in the study of the early evolution of multicellular animal phylum. The Chengjiang biota (about 520Ma) in eastern Yunnan is a treasure trove of fossils specifically buried in the early Cambrian period, documenting the early radiative evolution of animal phylum during the Cambrian explosion.

"Cupworms" are a type of fossil endemic to the Cambrian specific buried fossil group, and in the past only 1 genus and 2 species of cupworms have been reported. Zhao Yang, a doctoral student at the Key Laboratory of Paleontology Research in Yunnan Province, under the guidance of his supervisor Cong Peiyun, carried out systematic research on many fossil specimens of peduncula worms in the Chengjiang biota, and identified a new genus of Trichophyllum Dai flowerworm. In the process of cooperation with the University of Bristol in the United Kingdom, the Natural History Museum in London, and Yale University in the United States, Dr. Zhao Yang, Cong Peiyun, Hou Xianguang and Wei Fan conducted further comprehensive research on many fossil species with similar morphological characteristics and body structure in the Cambrian Period, and confirmed that the composite cilia structure is a common feature of these fossil taxa, and is homologous with the ctenophores (cilia clusters) of living ctenophores.

Using bayesian methods, the team conducted a systematic analysis of the matrix constructed from 93 taxa and 278 morphological features, and the results supported that benthic solid fossil taxa such as "peduncles" were stem groups of living ctenophores, indicating that the composite cilia structure of early ctenophores was mainly used for filter feeding in the early days. Integrating all the ctenophore fossil taxa in the early and middle Cambrian periods, the team first proposed a new hypothesis about the evolution of ctenophores' body shape, that is, the living planktonic ctenophores evolved from the early types of solid filter feeding through the specialization and degradation of different body structures. The results also show that the diversity of ctenophores has reached a high level during the Cambrian explosion of life, with solid ctenophores and planktonic ctenophores living together in the same period of geological history.

This study was jointly funded by the National Natural Science Foundation of China and the Science and Technology Department of Yunnan Province. Zhao Yang, phD candidate of The Key Laboratory of Paleontology Research of Yunnan Province, Yunnan University, is the first author, and Researcher Cong Peiyun is the corresponding author.

Guangming Daily ( 2019-03-22 08 edition)