Scorpionflies Were Devastated by the End of the Eocene Climate

Simon Fraser University biologists have discovered a new, extinct family of insects that will help scientists better understand how some animals responded to global climate change and the evolution of communities.

The Eocene Apex of Panorpoid Family Diversity, a paper by SFU's Bruce Archibald and Rolf Mathewes, plus David Greenwood from Brandon University, was recently published in the Journal of Paleontology.

The researchers named the new family the Eorpidae, after the Eocene Epoch, the age when these insects lived some 50 million years ago. The fossils were found in British Columbia and Washington state, most prominently at the McAbee Fossil Beds near Cache Creek, B.C.

This new family raises questions about its extinction. Insect families have steadily accumulated since before the Eocene, with few, scattered losses—apart from the distinct exception of a cluster of family extinctions within a group of scorpionflies that includes the Eorpidae.

"The Eorpidae was part of a cluster of six closely related families in the Eocene, but today this group is reduced to two. Why were these different?" says Archibald. "We believe the answer may lay in a combination of two large-scale challenges that would have hit them hard: the evolutionary diversification of a strong competitive group and global climate change."

In a major evolutionary diversification, ants evolved from a small group to become major ecological players in the Eocene, now competing with these scorpionflies for the same food resource in a whole new, efficient manner.

Global climates were much warmer 50 million years ago, associated with increased atmospheric carbon, a relationship that scientists see today. Along with this, winters were mild, even in the cool, higher elevations where these insects lived. Average temperatures there were similar to modern Vancouver, but with few—if any—frost days.

When climates outside of the tropics later cooled, temperature seasonality also widened, forming the modern pattern of hot summers and freezing winters. Plant and animal groups that inhabited Eocene uplands either had to evolve tolerance for colder winters, migrate to the hot tropics and adapt to that climate, or go extinct.