platyrrhine vs platyrhinian

platyrrhine is a noun but platyrhinian is not a noun.

Word	Noun	Adjective	Verb	Adverb
platyrrhine	Yes	Yes	No	No
platyrhinian	No	Yes	No	No

As adjectives, platyrrhine and platyrhinian are synonyms defined as:

platyrrhine and platyrhinian: of or related to New World monkeys having nostrils far apart or to people with broad noses

Other synonyms of platyrrhine include broadnosed, platyrhine, platyrrhinian, platyrrhinic.

platyrrhine (noun)	platyrhinian (noun)
hairy-faced arboreal monkeys having widely separated nostrils and long usually prehensile tails

platyrrhine (adjective)	platyrhinian (adjective)
of or related to New World monkeys having nostrils far apart or to people with broad noses	of or related to New World monkeys having nostrils far apart or to people with broad noses