51�Թ�

“Sometimes it’s very easy to see exactly where the muscle was placed, because it leave stress marks or ridges on the skull,” says Nilsson.

"The closest analog we can find to the 'stress marks' that we observed in Antarctic Lystrosaurus tusks are stress marks in teeth associated with hibernation in certain modern animals," Whitney added.

It's a complicated milieu, but one of the main ways that stress marks the brain is through epigenetics.

The choleric brows went up like twin stress marks accenting unspoken skepticism.