Scientists found that a commonly used protocol hides the true extent of how species live and die through major extinctions. The clams above are assumed to have originated before the last great extinction, but an improved methodology suggests they actually originated after the extinction. The Field Museum is in Chicago.
There are extinctions and the Great Dying. The extinction of life on Earth happened around 250 million years ago.
A new study finds that a common methodology may obscure the true picture of which species and lineages are destroyed during mass extinctions.
The study evaluated hundreds of species of fossil clams to piece together a comprehensive evolutionary tree over hundreds of millions of years. The scale of evolutionary recovery from a massive extinction can be off by as much as 400% if a basic assumption is made in most models.
The assumption is that when a new species is created, it splits the lineage into two new species, which will make the original species extinct. A clam known as Species A might split into two other clam species, and it is considered extinct.
Sometimes a new lineagebuds off an existing one. Even if Species A continues to exist, clam Species B might be born.
"You can end up with two totally different pictures depending on what assumptions you bake into the model," said David Jablonski, the William R. Kenan Jr. distinguished service Professor of Geophysical Sciences at the University of Chicago.
"There are many important questions locked up in these evolutionary trees," said Nick Crouch, a UChicago researcher and corresponding author of the study. They are the underpinning of almost every evolutionary study out there right now. We need to accurately know when the ancestors go extinct and when they start again.
Cultivating trees that are evolutionary.
For a long time, scientists were only able to look at fossils to understand evolution. Fossils are useful, but there are many different types of creatures that don't fossilize easily. "I study clams so I have tons of fossils, but my colleagues studying fruit flies aren't so lucky," said Jablonski.
The ability to analyze DNA was a boon for scientists.
New genes are acquired and old genes are retained as DNA is passed down. Even if we don't have fossils, scientists can make estimates about the evolution of a modern-day organism by studying its genes.
There are a lot of assumptions built into that type of analysis. They wanted to run an experiment to see how assumptions affect results and compare the results between different assumptions.
An illustration of the issue that arises when using the "forking" assumption. When a mass extinction occurs in the uncertain area, it can distort the true picture of how species respond to extinctions. The credit was given to Crouch et al.
Bivalves are a type of aquatic mollusk that includes scallops, oysters and mussels. There is an extensive fossil record from all over the world, because these organisms all have hard shells that fossilize quickly.
A comprehensive picture for all bivalves was developed by the Field Museum, with the help of a number of people. "It did involve a certain level of obsessiveness," he said.
The process gave them a good idea of what the bivalve family tree looked like. The numbers were run using the "forking" assumption and then run again with the "budding" approach.
They found a big difference. "You might not expect a simple decision to have a big effect," he said. If you force that assumption on your data, you lose some of the big picture.
The fossil record indicated that the origins of new lineages were pushed further back in time than they actually were. The forking assumption is that clams B and C must have both come from the same place, because new lineages always arrive in pairs. clam C may not have evolved until much later, so forking tends to start new lines earlier.
The splitting approach hides the true effects of mass extinction and the rebound that follows.
"From fossils, we see a dramatic evolutionary burst after a mass extinction like the one at the end of the Mesozoic Era, when the dinosaurs went down and the descendants, the birds, took off, along with mammals like us," said Jablonski. The splitting approach tends to make the picture around mass extinctions look less realistic.
The forking method suggests that seven major lineages emerged after the extinction. The fossil record says it was 28. "That's a four-fold difference," he said.
Mass extinctions are important in how biologists understand evolution. There are completely wiped out and new ones that emerge. They're a major factor in evolution.
The scientists got a picture that was much more similar to the fossil record by using an evolutionary model that allowed for budding instead of splitting.
The scientists hope that the results will help them improve their tree studies. There are many types of life, from mosses to squids to birds.
The scientists said that the work was made possible by collaboration. The group brings researchers together in a wide range of fields. That led to a powerful set of analyses, according to UChicago's Committee on Evolutionary Biology. "We couldn't have done it without this team."
Nicholas M. A. Crouch and his team have studied the effects of bifurcation and budding on the evolution of the bivalve families in the Proceedings of the Royal Society B: Biological Sciences. There is a book titled "PukiWiki"
The Royal Society B has a journal.
The fossils were retrieved from thephys.org on December 2, 2021.
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