Mass Extinctions Set the Pace

The rate of evolution is affected for millenia after mass extinctions.

Jul 5, 2012
Hayley Dunning

BivalvesWIKIMEDIA COMMONS, MANFRED HEYDE

Mass extinction events empty many ecological niches, usually leading to explosions in speciation as new groups of organisms rush to claim them. It is commonly assumed that after this initial growth, the number of new species evolving declines back to a normal rate. However, a new analysis published last week (June 30) in Geology suggests that new, often faster rates of speciation prevail for hundreds of years after widespread extinctions.

“Things don’t return to what they were before,” study co-author Andrew Krug said in a press release. “They operate at a different pace, sometimes more rapidly, other times more slowly.” The new pace also seems to be permanent, until the next mass extinction.

The team looked into the diversity of bivalves, the group of mollusks that includes clams and oysters, from the start of the Jurassic period, 200 million years ago, to the end of the Pleistocene Epoch, just 10,000 years ago. The bivalve groups evolved at steady rates for millions of years, but that rate shifted dramatically in step with mass extinctions, in a pattern co-author David Jablonski described as “surprisingly organized.”