Psilopterus (Greek for "bare wing") is an extinct genus of phorusrhacid ("terror bird") from the Middle Oligocene to possibly the Late Pleistocene of Argentina and Uruguay.

The most important diagnostic characteristics are a low skull and upper jaw (or maxilla; similar to the mesembriornithine phorusrhacids)[1] and the extreme slant of the front edge of the hole just before the eye (rostal portion of the antorbital fenestra), though there are also differences in the rest of the skeleton.

[7] The species is defined by part of a lower leg bone (the lectotype, MLP-162, is the distal end of a tibiotarsus), but a wide variety of material has been referred to the taxon.

[8] A number of discrepancies between various specimens have been attributed to differences in age or sex, but material currently assigned to P. lemonei and P. bachmanni may be reclassified at the species level if reexamined in depth.

P. affinus is one of several species known from fragmentary material found in 1899 in the Chubut Province of Argentina (Patagonia), in rocks which dated to the Middle to Late Oligocene (Deseadan).

Known only from a single incomplete skeleton that includes parts of the jaw, arm, and leg (holotype MLP-76-VI-12-2), the species is defined by a groove in the front of the thigh bone (trochlea).

[16] The following phylogenetic tree shows the internal relationships of Phorusrhacidae under the exclusion of Brontornis as published by Degrange and colleagues in 2015, which recovers Psilopterus as the only member of Psilopterinae as a sister clade to Mesembriornithinae.

[17] Psilopterus bachmanni & lemoinei lived during the middle Miocene in the Santa Cruz Formation, which preserves mostly a coastal environment, but also forested and grassland regions.

[20] Psilopterus lemoinei is also known from the coastal Monte Leon Formation that was in the same region in Santa Cruz, but part of the older lower Miocene age.