au·toch·tho·nous [aw tókth?n?ss] adjective 1. biology present from earliest times: descended from the original flora, fauna, or inhabitants of the region in which it is found. See also allochthonous (sense 2) 2. geology formed where found: describes a rock, mineral deposit, or geologic feature that was formed in the area where it is found 3. physiology produced where situated: describes a physical function or disorder that originates in the part of the body where it is found