A. obscurus is a rare species endemic to Argentina and Uruguay. It is similar to A. marginatus in body size and shape of pronotum and elytra. In both species the integument is covered with lanceolate scales and setae, but in A. obscurus scales are grey and setae are coarse, short and recumbent.
This species is flightless and the absence of males suggests that is probably parthenogenetic (Lanteri & Normark 1995).
Unknown.
Associated with vegetation of the gallery forests of Paraná, Uruguay and La Plata rivers.