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Significant Energy Events in Earth's and Life's History as of 2014
One of Peter Ward’s recent hypotheses is that animals that adapted to the changing conditions, particularly when oxygen levels crashed, survived the catastrophes to dominate the post-catastrophic environment. In the late Permian, several therapsid lines developed , which may have been used for respiratory water retention in a world where oxygen levels were crashing. This is a controversial issue, and related to the controversy over when reptiles developed . The therapsid ancestors of mammals, , first appeared about 260 mya, and had many .
c. 4.6 billion years ago (“bya”)
The appeared in the late Carboniferous and looked like a modern lizard. It also had some canine-type teeth. Diapsids, however, were marginal animals in the Permian, as that was the time of synapsid and therapsid dominance. Diapsids would not rise to prominence until the Triassic.