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promammal

noun
pro·​mammal | \ (ˈ)prō+\

Definition of promammal

1 : an extinct reptile exhibiting definite mammalian characteristics especially : a synapsid reptile
2a : a primitive mammal (as a platypus) not exhibiting all the characteristics of the group
b : one of the Protomammalia

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History and Etymology for promammal

pro- entry 1 + mammal

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