monotreme vs prototherian

monotreme and prototherian both are nouns.

Word	Noun	Adjective	Verb	Adverb
monotreme	Yes	No	No	No
prototherian	Yes	No	No	No

As nouns, prototherian is a hypernym of monotreme; that is, prototherian is a word with a broader meaning than monotreme:

monotreme: the most primitive mammals comprising the only extant members of the subclass Prototheria
prototherian: primitive oviparous mammals found only in Australia and Tasmania and New Guinea

monotreme (noun)	prototherian (noun)
the most primitive mammals comprising the only extant members of the subclass Prototheria	primitive oviparous mammals found only in Australia and Tasmania and New Guinea