(ORDO NEWS) — The ancestors of many animal species living today may have lived in a river delta in what is now China, a new study suggests.
Chengjian, a city in China’s mountainous Yunnan province, is believed to be the origin of many modern animal species, including humans.
It was in this place that complex organisms first arose – an event known as the “Cambrian explosion”, an important period in the history of the Earth.
The Ediacaran and Cambrian periods lasted about half a billion years ago. But hidden in the genetic code of modern animals are signs of when the main groups of animals first arose.
The 518-million-year-old Chengjiang biota (Yunnan, southwestern China) is one of the oldest fossil groups known to science and a key record of the Cambrian Explosion.
More than 250 animal species have been found there, including various worms, arthropods (ancestors of living shrimps, insects, spiders, scorpions) and even the earliest vertebrates (ancestors of fish, amphibians, reptiles, birds and mammals).
The new study found for the first time that this environment was a shallow offshore delta rich in nutrients and prone to storm flooding.
The area is currently onshore in the mountainous province of Yunnan, but the team examined rock core samples that show evidence of sea currents in the past environment.
The Cambrian Explosion is now generally accepted as a real rapid evolutionary event, but the causative factors of this event have long been discussed, hypothesized about ecological, genetic or environmental triggers,” says senior study author Dr Xiaoya Ma, a paleobiologist at the University of Exeter and the University of Yunnan.
The discovery of a deltaic environment has shed new light on the possible causal factors for the flourishing of these animal-dominated bilateral animal-dominated marine communities and their exceptional soft tissue preservation.”
“Unstable environmental stressors may also have contributed to the adaptive radiation of these early animals.”
Study co-author Farid Saleh, a sedimentologist and taphonomist at Yunnan University, said: “From the association of numerous sedimentary flows, we can see that the environment in which the Chengjiang biota lived was complex and certainly shallower than previously suggested in the literature for similar animal communities. “.
Changshi Qi, another co-author and a geochemist at Yunnan University, added: “Our study shows that Chengjiang’s biota mostly lived in a well-oxygenated, shallow deltaic environment.
“Storm floods carried these organisms to nearby deep, oxygen-deficient sites, resulting in the exceptional survival we see today.”
Co-author Louis Buatua, a paleontologist and sedimentologist at the University of Saskatchewan, said: “The Chengjiang biota, like similar faunas described elsewhere, is preserved in fine-grained sediments.
“Over the past 15 years, our understanding of how these mud deposits were deposited has changed significantly.
“Applying this newly acquired knowledge to the study of exceptionally preserved fossil deposits will fundamentally change our understanding of how and where these deposits 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.
This contrasts with earlier studies 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 M. Gabriela Mangano, a paleontologist at the University of Saskatchewan who has studied other known sites of exceptional preservation in Canada, Morocco and Greenland.
Maximiliano Paz, a postdoctoral fellow at the University of Saskatchewan specializing in fine-grained systems, added: “Access to sediment cores allowed us to see details in the rock that are usually difficult to appreciate in weathered outcrops in the Chengjiang area.”
This work is an international collaboration between the University of Yunnan, the University of Exeter, the University of Saskatchewan, the Chinese Academy of Sciences, the University of Lausanne, and the University of Leicester.
The study was funded by the China Postdoctoral Science Foundation, the China Natural Science Foundation, the National Key Laboratory of Paleobiology and Stratigraphy, the Natural Sciences and Engineering Research Council of Canada, and the George J. McLeod Department of Geology.
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