Mean atmospheric O2
Geologic Time Scale
A pair of three-foot-long leponspondyl amphibians of the genus Diplocaulus swim near the bottom of a fresh water Permian lake 290 million years ago in what is today Texas. Diplocaulus is recognized for its large, boomerang-shaped head. With no known counterpart today, the purpose of Diplocaulus' head is not clear. It may have helped it to swim, and/or its bony head may have made it difficult for larger marine predators to swallow.
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