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the·rap·sid | \ thə-ˈrap-səd 
\
\Definition of therapsid
: any of an order (Therapsida) of advanced synapsid vertebrates that flourished during the Permian and Triassic periods with the last forms becoming extinct during the Cretaceous period and that are considered ancestors of the mammals
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The first known use of therapsid was in 1912
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