pelycosaur
noun
pel·​y·​co·​saur
| \ ˈpe-li-kə-ˌsȯr
\
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Definition of pelycosaur
: any of an order (Pelycosauria) of extinct, primitive, synapsid vertebrates (such as dimetrodonchiefly of the Permian period often having extreme development of the dorsal vertebral processes and giving rise to the therapsids
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