A long-standing question has been answered – how mass extinctions paved the way for clams and oysters

The researchers used Bayesian analysis to study the decline of brachiopods and the rise of bivalves after the end-Permian extinction, and found that bivalves were better adapted to changing conditions. Left, Devonian brachiopod fossils from Ohio, USA. Right, modern bivalve shells from Shell Beach, Western Australia. Credit: (Wikimedia Commons; Creative Commons CC0 1.0 Universal Public Domain Assignment) for the image on the left. The photo on the right is by Zhong-Qiang Chen.

One of the greatest crises in Earth’s history, marked by a major shift in shellfish, saw the widespread replacement of brachiopods, often referred to as ‘lamp shells’, by bivalve ones. Classify Such as oysters and clams. This occurred as a result of the devastating mass extinction at the end of the Permian, which effectively reset the evolution of life approximately 250 million years ago.

Research by paleontologists in Bristol, UK, and Wuhan, China has shed new light on this crucial transition when ocean ecosystems changed from ancient to modern.

Life on land and in the sea is rich and forms certain ecosystems. In modern oceans, animals such as bivalves, gastropods, corals, crustaceans, and fish dominate the seafloor. But these ecosystems all date back to the Paleolithic era Triassic When life came back from the brink. During that crisis, only one in twenty species survived, and there has been a long debate about how new ecosystems were built and why some groups survived, while others did not.

Brachiopods dominated the shelled animals before the extinction, however, bivalves flourished afterward, better adapting to their new conditions.

“One classic case was the replacement of bivalves by brachiopods,” explained Chen Guo, from Wuhan and Bristol, who led the project. “Paleontologists used to say that bivalves were better competitors and thus somehow beat out brachiopods during this period of crisis. There is no doubt that brachiopods were the main group of shelled animals before the extinction, and were replaced by bivalves afterwards.”

Diversities of brachiopods and bivalves over the past 500 million years

Diversities of brachiopods and bivalves over the past 500 million years, showing a switch between brachiopods and bivalves near the Permian-Triassic boundary. Credit: Chen Guo et al

“We wanted to explore the interactions between brachiopods and bivalves across their long history, especially in the Permian-Triassic period,” said study co-author Joe Flannery Sutherland. “So we decided to use a computational method called Bayesian analysis to calculate rates of origination, extinction, and preservation of fossils, as well as test whether brachiopods and bivalves interacted with each other. For example, did the emergence of bivalves cause the decline of brachiopods?”

“We found that, in fact, the two groups share similar trends in diversification dynamics during a time of crisis,” said Professor Michael Benton from Bristol’s School of Earth Sciences. “This means that they were not actually competing or preying on each other, but were most likely both responding to similar external drivers such as sea temperature and short-term crises. But bivalves eventually prevailed, and bivalves retreated to deeper waters, where they are still found.” , but in smaller numbers.

Professor Zhongqiang Chen from Wuhan commented: “It was fascinating to see how modern computational methods can address such a long-standing question.

“We have always thought that the end-Permian mass extinction marked the end of brachiopods, and that was the case. But it appears that both brachiopods and bivalves were hit hard by the crisis, and both recovered in the Triassic, but bivalves could adapt significantly.” Better with higher ambient temperatures.So, that gave them the advantage, and then JurassicTheir numbers have skyrocketed, and the brachiopods haven’t done much.

“I had to examine and compile records of more than 330,000 fossil brachiopods and bivalves over the course of the study, and then do the Bayesian analysis, which took weeks and weeks on the Bristol supercomputer,” Zhen Guo said. “But I like this method because it repeats everything millions of times to take into account all Types of uncertainty in the data and gives a great deal of rich information about what was happening.

“The end-Permian mass extinction was the largest ever recorded, and it reset evolution dramatically,” Professor Benton concluded. “Indeed, 50 million years after the crisis, the Triassic saw a revolution in life on land and in the sea. Understanding how life came back from near-annihilation and thus laid the foundation for modern ecosystems is one of the big questions in macroevolution. I’m sure we haven’t Move the final word here though!

Reference: “Bayesian analyzes suggest that bivalves were not the cause of the fall of brachiopods following the Permian-Triassic mass extinction” by Zhen Guo, Joseph T. Flannery-Sutherland, Michael J. Benton, and Zhong-Qiang Chen, 9 September 2023, Nature Communications.
doi: 10.1038/s41467-023-41358-8

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