promammal

\(ˈ)prō+\ noun

Etymology: pro- (I) + mammal

1. : an extinct reptile exhibiting definite mammalian characteristics; especially : a synapsid reptile

2.

a. : a primitive mammal (as a platypus) not exhibiting all the characteristics of the group

b. : one of the Protomammalia

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promammal etc.:

see pro-² 1.