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PALEOZOIC ERA

PERMIAN PERIOD

299-252 million years ago

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therapsid

Therapsid fossils show evidence of being warm-blooded.

The microscopic structure of their bone (the lack of growth rings, the well developed and abundant haversian canal system of blood vessels) suggests that they were endothermic (“warm blooded”) although probably not as endothermic as mammals (Kemp, 1982; Carroll, 1988).