There was the Permian–Triassic extinction event, the "great dying", where apparently the only large land animals to survive were the therocephalians and their p

There was the Permian–Triassic extinction event, the "great dying", where apparently the only large land animals to survive were the therocephalians and their prey lystrosaurus, and for both their survival seems to be due to burrowing. CO2 had hit 0.25%.