prototherian/ˌpɹoʊtɵˈθɪəɹi.ən/EtymologyFrom translingual Prototheria + -an, from Ancient Greek πρωτο- (prōto-, “proto-, first”) + θηρίον (thēríon, “beast”).adjBelonging or pertaining to the subclass Prototheria.“It is evident that the Edentates are widely separated from all other existing Eutherians; and Professor W. K. Parker, in view of the tendency to a variation in the number of cervical vertebræ and other features, has suggested a separate origin from a Prototherian stock.”nounAny of the egg-laying mammals of the subclass Prototheria; a monotreme.“Monotremes (prototherians), which include the duck-billed platypus, and short- and long-beaked echidnas, have a cloaca—a single opening for the fecal, urinary, and reproductive tracts.”