It takes at least 10 million years for life to fully recover after a mass extinction, a speed limit for the recovery of species diversity that is well known among scientists. Explanations for this apparent rule have usually invoked environmental factors, but research led by The University of Texas at Austin links the lag to something different: evolution.
The recovery speed limit has been observed across the fossil record, from the “Great Dying” that wiped out nearly all ocean life 252 million years ago to the massive asteroid strike that killed all nonavian dinosaurs. The study, published April 8 in the journal Nature Ecology & Evolution, focused on the later example. It looks at how life recovered after Earth’s most recent mass extinction, which snuffed out most dinosaurs 66 million years ago. The asteroid impact that triggered the extinction is the only event in Earth’s history that brought about global change faster than present-day climate change, so the authors said the study could offer important insight on recovery from ongoing, human-caused extinction events…
In other words, mass extinctions wipe out a storehouse of evolutionary innovations from eons past. The speed limit is related to the time it takes to build up a new inventory of traits that can produce new species at a rate comparable to before the extinction event. Paper. (paywall) – Christopher M. Lowery, Andrew J. Fraass. Morphospace expansion paces taxonomic diversification after
end Cretaceousmass extinction. Nature Ecology & Evolution, 2019; DOI: 10.1038/s41559-019-0835-0 More.
While this may turn out to be true, the apparently fixed rate of change implies a more regulated system than the random developments that we are used to associating with evolution.
One interpretation of the claim cites the concept of morphospace:
Morphospace, short for “morphological space”, is a way for scientists to visualise the possible shape and structure of organisms, the physical phenotype. A morphospace can show all possible forms, and how many of those have been taken on by organisms in the real world. …
What Lowery and Fraass discovered is that the fossil record for marine plankton shows that increasingly complex morphologies are linked to episodes of taxonomic diversification, with the latter being dependent on the former. Newly occupied morphospaces opened up room for increasing radiation, just as the morphospace reconstruction hypothesis predicted.
Importantly, their work indicates that the constraints of morphospace colonisation might impose a “speed limit” on post-extinction taxonomic diversification. This is a sobering reminder that if we are in the midst of an anthropogenic extinction event, the biosphere will take millions of years to get over it. Stephen Flieschfresser, “Mass extinction recovery governed by “morphospace”” at Cosmos
One can really only test this thesis for the distant past but structuralist, who think evolution is governed by fixed laws, should find it of interest.
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