Modern animal life may have its origins in a shallow, nutrient-rich delta

Arthropod (Naroia). Credit: Dr. Xiaoya Ma

The ancestors of many animal species alive today may have lived in a delta in present-day China, according to new research.

The Cambrian Explosion over 500 million years ago saw the rapid spread of bilateral species – symmetrical along a central line, like most animals today (including humans ).

The 518-million-year-old Chengjiang biota – in Yunnan, southwest China – is one of the oldest groups of animal fossils currently known to science and a key record of the Cambrian explosion.

Fossils of more than 250 species have been found there, including various worms, arthropods (ancestors of living shrimps, insects, spiders, scorpions) and even the first vertebrates (ancestors of fish, amphibians, reptiles, birds and mammals).

The new study reveals for the first time that this environment was a shallow, nutrient-rich marine delta affected by storm flooding.

Myllokunmingia

Fish (Myllokunmingia). Credit: Dr. Xiaoya Ma

The area is now on land in the mountainous province of Yunnan, but the team studied rock core samples that show evidence of sea currents in the past environment.

“The Cambrian Explosion is now universally accepted as a truly rapid evolutionary event, but the causal factors of this event have long been debated, with assumptions about environmental, genetic or ecological triggers,” said lead author Dr. Xiaoya Ma, a paleobiologist at the University of Exeter and Yunnan University.

“The discovery of a deltaic environment has shed new light on understanding possible causal factors for the flourishing of these Cambrian bilateral animal-dominant marine communities and their exceptional soft-tissue preservation.

“Unstable environmental stressors could also contribute to the adaptive radiation of these early animals.”

Lobopod worm (Luolishania)

Lobopod worm (Luolishania). Credit: Dr. Xiaoya Ma

Co-lead author Farid Saleh, a sedimentologist and taphonomist at Yunnan University, said: “We can see from the association of many sedimentary flows that the environment hosting Chengjiang biota was complex and certainly shallower. than previously suggested in the literature for similar animal communities.

Changshi Qi, the other co-lead author and geochemist at Yunnan University, added, “Our research shows that Chengjiang biota mainly lived in a well-oxygenated shallow-water deltaic environment.

“Storm flooding transported these organisms to adjacent deep, oxygen-poor environments, leading to the exceptional preservation we see today.”

Co-author Luis Buatois, a paleontologist and sedimentologist at the University of Saskatchewan, said: “Chengjiang biota, like similar faunas described elsewhere, are preserved in fine-grained deposits.

“Our understanding of how these muddy sediments were deposited has changed dramatically over the past 15 years.

“The application of this newly acquired knowledge to the study of fossiliferous deposits of exceptional preservation will radically change our understanding of how and where these sediments accumulated.”

The results of this study are important because they show that most early animals tolerated stressful conditions, such as fluctuations in salinity (salt) and large amounts of sediment deposition.

This contrasts with previous research suggesting that similar animals colonized deeper, more stable marine environments.

“It’s hard to believe that these animals were able to cope with such a stressful environment,” said Dr. Gabriela Mángano, a paleontologist at the University of Saskatchewan who has studied other well-known sites of exceptional preservation in Canada. , in Morocco. , and Greenland.

Maximiliano Paz, a postdoctoral fellow at the University of Saskatchewan who specializes in fine-grained systems, added, “Access to sediment cores has allowed us to see details in the rock that are typically difficult to appreciate. in weathered outcrops in the Chengjiang region.

This work is an international collaboration between Yunnan University, University of Exeter, University of Saskatchewan, Chinese Academy of Sciences, University of Lausanne and University of Leicester.

The research was funded by the Chinese Postdoctoral Science Foundation, the Natural Science Foundation of China, the State Key Laboratory of Palaeobiology and Stratigraphy, the Natural Sciences and Engineering Research Council of Canada, and the George J. McLeod Enhancement Chair in Geology.

The article, published in the journal Nature Communicationis titled: “Chengjiang biota inhabited a deltaic environment.”

Reference: “The Chengjiang Biota inhabited a deltaic environment” by Farid Saleh, Changshi Qi, Luis A. Buatois, M. Gabriela Mángano, Maximiliano Paz, Romain Vaucher, Quanfeng Zheng, Xian-Guang Hou, Sarah E. Gabbott and Xiaoya Ma, March 23, 2022, Nature Communication.
DOI: 10.1038/s41467-022-29246-z

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