I've heard it said that the Anomalies generate extra O2 into the atmosphere around themselves. This is what makes it possible for critters from oxygen-rich eras to not pass out. (ie, the Gorgonopsid and giant spider)
But what about creatures from eras where the oxygen content was lower than it is nowadays? Animals from the Triassic (for example) are in a lot of trouble, it seems.
Of course, I could be wrong.
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