autochthonous vs autochthonic

autochthonous and autochthonic both are adjectives.

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

As adjectives, autochthonous and autochthonic are synonyms defined as:

Other synonyms of autochthonous include autochthonal, endemic, indigenous.

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