Evolutionary stasis in synapsid encephalization during the end-permian mass extinction

Area of Science:

• Paleoneurology
• Evolutionary Biology
• Paleontology

Background:

• Brain size and encephalization are linked to extinction risks.
• The end-Permian mass extinction's paleoneurological impact is understudied.
• Synapsids, the forerunners of mammals, are key to understanding this period.

Purpose of the Study:

• Investigate brain evolution in synapsids across the end-Permian mass extinction.
• Test predictions of brain size increase or decrease during mass extinctions.
• Examine the role of paleoneurology in evolutionary outcomes.

Main Methods:

• Utilized Synchrotron Radiation and CT scanning for brain endocast analysis.
• Conducted a phylogenetic survey of synapsids spanning the Permian-Triassic boundary.
• Analyzed evolutionary rates to understand selection pressures.

Main Results:

• Observed unexpected stasis in the encephalization quotient of synapsids during the extinction.
• Found that stabilizing selection did not explain the lack of change.
• Hypothesized resource limitations impeded neuroplasticity and prolonged stasis.

Conclusions:

• The end-Permian mass extinction did not drive immediate brain size adaptation in synapsids.
• A lack of resources may have prevented adaptive brain evolution.
• Post-extinction, brain size variability re-emerged, initiating mammalian brain evolution.