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Can the fallout from mass extinctions enable prediction of patterns in evolution?


A recent study suggest yes:

The study builds on recent Stanford research that looked at body size and extinction risk among marine animals in groupings known as genera, one taxonomic level above species. That study found smaller-bodied genera on average are equally or more likely to than their larger relatives to go extinct.

The new study found this pattern holds true across 10 classes of marine animals for the long stretches of time between mass extinctions. But mass extinctions shake up the rules in unpredictable ways, with extinction risks becoming even greater for smaller genera in some classes, and larger genera losing out in others.

The results show smaller genera in a class known as crinoids — sometimes called sea lilies or fairy money — were substantially more likely to be wiped out during mass extinction events. In contrast, no detectable size differences between victims and survivors turned up during “background” intervals. Among trilobites, a diverse group distantly related to modern horseshoe crabs, the chances of extinction decreased very slightly with body size during background intervals — but increased about eightfold with each doubling of body length during mass extinction.

When they looked beyond the marine genera that died out to consider those that were the first of their kind, the authors found an even more dramatic shift in body size patterns before and after extinctions. During background times, newly evolved genera tend to be slightly larger than those that came before. During recovery from mass extinction, the pattern flips, and it becomes more common for originators in most classes to be tiny compared to holdover species who survived the cataclysm.

Gastropod genera including sea snails are among a few exceptions to the build-back-smaller pattern…

Stanford University, “Extinction and origination patterns change after mass extinctions” at ScienceDaily (October 6, 2021)

The description makes clear that evolution is seen as an intelligent agent, like a coach deploying players:

Think of this as the biosphere’s version of choosing starters and benchwarmers based on height and weight more than skill after losing a big match. There may well be a logic to this game plan in the arc of evolution. “Our next challenge is to identify the reasons why so many originators after mass extinction are small,” said senior author Jonathan Payne, the Dorrell William Kirby Professor at Stanford Earth.

Stanford University, “Extinction and origination patterns change after mass extinctions” at ScienceDaily (October 6, 2021)

But can evolution be both mindless and a strategic coach?

The paper is closed access.


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