autochthonous vs autochthonal

autochthonous and autochthonal both are adjectives.

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

As adjectives, autochthonous and autochthonal are synonyms defined as:

Other synonyms of autochthonous include autochthonic, endemic, indigenous.

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