How the Most Diverse Assemblage of Cambrian Organisms Dwelt in China's River Delta over 500 Million Years Ago

Ancestors of many of the modern animal species we know today could have lived in China's river delta according to a recent study published.

500 Million Year Old Animal Ancestor: the Chengjiang Biota

Yunnan, China the site for the Chengjiang Biota

(Photo: STR/AFP via Getty Images)
OPSHOT - This aerial photo taken on July 7, 2019 shows the main structure of the Jimingsansheng Bridge (L) in Xuyong county in Luzhou City in China's southwestern Sichuan province. - The bridge joins southwest China's Yunnan, Guizhou and Sichuan provinces.

More than 500 million years ago, the Cambrian Explosion occurred. The rapid evolution of bilaterian species that had mirror halves joined by a central median line, like most animal species including humans, spread throughout the globe.

Meanwhile, the 518-million-year-old Chengjiang Biota found in Yunnan, south-west China is one of the oldest and most adverse assemblages of animal fossils known to science which serves as a key record of the momentous Cambrian Explosion, according to ScienceDaily.

Fossils of over 250 species have been found in the Biota including several worms, arthropods, and the earliest vertebrates.

The recent study published in the journal Nature, titled "The Chengjiang Biota inhabited a deltaic environment" found that for the first time ever that the environment was in fact a shallow-marine, nutrient-rich delta affected heavily by storm floods.

Today, the area consists of solid landmasses in what is now the mountainous Yunnan Province, however, upon analysis of rock core samples the team discovered that the environment had marine currents in the past.

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Understanding the Causal Triggers for the Chengjiang Biota

Dr. Xiayo Ma, senior author of the study, and paleobiologists from the University of Exeter and Yunnan University explains that the Cambrian Explosion is universally accepted as a genuine event of rapid evolution, however, causal factors for the event have been widely debated. The current hypotheses involve environmental, ecological, and genetic triggers report DailyMail.

She adds that the recent discovery of the deltaic environment paves the way to new understandings of the possible factors that caused the flourishing of Cambrian bilaterian animal-dominated marine communities and the preservation of their soft tissues. Adding that the unstable environment might have played a role in the adaptive radiation of the early animal species.

Farid Saleh, co-lead author of the study and a sedimentologist and taphonomist from Yunnan University says that we can see, based on the association of various sedimentary flows hosted by the environment, that the Chengjiang Biota was extremely complex and shallower than previously suggested.

Co-author and geochemist from Yunnan University, Changsi Qi, explains that the recent research shows that the diverse Chengjian Biota mainly dwelled in well-oxygenated shallow-water deltaic environments. Wherein storm floods may have transported the organisms down to the adjacent deep oxygen-deficient environment which led to the exceptional preservation that scientists see today.

Luis Buatois, a co-author, adds that similar to other preserved faunas, the Chengjiang Biota was preserved in fine-grained sedimentary deposits. Wherein science's understanding of how the sediments were deposited has dramatically changed in the past 15 years.

Results of the recent study are vital in understanding the previous environment where many of the ancestors of today's species dwelt because it shows how early animals tolerated highly stressful conditions such as fluctuations in salinity, and high amounts of sediment deposition.