How did Earth's biggest mass extinction affect the brains of our distant ancestors?

The end-Permian mass extinction, which occurred about 252 million years ago, was the largest and most devastating mass extinction in Earth's history. Scientists have long wondered how surviving animals adapted to such an extreme global crisis. Using powerful Synchrotron X-rays and CT scanning, we reconstructed the brains of ancient mammal relatives that lived before, during, and after this catastrophic event. We expected to find that their brains either became larger to help them cope with rapidly changing environments, or smaller to conserve energy when food was scarce. Instead, we found something surprising: their brain size barely changed at all. We think the harsh conditions after the mass extinction may have limited the energy available for brain evolution, effectively putting brain development "on hold" for millions of years. Only after ecosystems recovered did brain size begin to change again, setting the stage for the evolution of the larger, more complex brains seen in mammals today. This study provides a fascinating new window into how life's greatest crisis shaped the evolutionary journey that eventually led to mammals—and ultimately, us.