Autochthon

(In addition to Webster's entry) One of the earliest known inhabitants of an area, an aborigine, or an indigenous plant or animal.
Geology uses this to refer to portions of the bedrock in a thrust fault that remain in place, while the nappe, or thrust sheet, moves.
Science fiction authors often use this term to refer to native alien life forms, when they want the creatures to sound more "exotic."

Au*toch"thon (?), n.; pl. E. Authochthons (), L. Autochthones (). [L., fr. Gr. , pl. , from the land itself; self + earth, land.]

1.

One who is supposed to rise or spring from the ground or the soil he inhabits; one of the original inhabitants or aborigines; a native; -- commonly in the plural. This title was assumed by the ancient Greeks, particularly the Athenians.

2.

That which is original to a particular country, or which had there its origin.

 

© Webster 1913.