autochthonic vs autochthonous

autochthonic and autochthonous both are adjectives.

Word	Noun	Adjective	Verb	Adverb
autochthonic	No	Yes	No	No
autochthonous	No	Yes	No	No

As adjectives, autochthonic and autochthonous are synonyms defined as:

Other synonyms of autochthonic include autochthonal, endemic, indigenous.

autochthonic (adjective)	autochthonous (adjective)
originating where it is found	of rocks, deposits, etc.; found where they and their constituents were formed
	originating where it is found