Previously, estimates of the earlier extinction had been made using fossils of invertebrates such as mollusks and clams, which are far more abundant.
With a larger dataset of vertebrates and analytical techniques borrowed from modern ecology, Sallan and Coates were able to see the abrupt changes in species composition before and after the Hangenberg event.
"It's a big extinction during what was already considered a critical time in vertebrate evolution, so it's surprising that it went unnoticed for so long," Sallan said. "But it took the right methods to reveal its magnitude."
What remains mysterious is exactly what happened 360 million years ago to trigger this mass extinction.
Other researchers have found evidence of substantial glacier formation at the end of the Devonian period, which would have dramatically lowered sea levels and affected life.
The first appearance of forest-like environments in some regions might also have produced atmospheric changes catastrophic to animal life.
The research also raises questions about the pattern of evolution after the extinction event.
It remains unclear why groups that were abundant before the event did not recover, while other groups spread and diversified in radical new ways.
Regardless of these questions, the consequences are still being felt hundreds of millions of years later.
"It is a pivotal episode that shaped modern vertebrate biodiversity," Coates said. "We are only now beginning to place that important event in the history of life and the history of the planet, which we weren't able to do before."
|Contact: Cheryl Dybas|
National Science Foundation