[2][3] This holotype consists of: an incomplete skull, the lower jaws, the proximal part of the coracoid and the second and ungual phalanges of digit II from the pes.

The fossils date to the Deseadan of the middle-upper Oligocene of the Deseado Formation of Cabeza Blanca (Chubut, Argentina).

[3] Two other specimens, a mandibular symphysis and incomplete left femur were collected from strata of the same age in Santa Cruz Province.

[2][3] In 2003 during their redescription of phorusrhacidae, Herculano Alvarenga and Elizabeth Hofling created a new subfamily, Patagornithinae, with Patagornis as the type genus, that included Andrewsornis and Andalgalornis.

[4] 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 a clade that contains Physornis, Phorusrhacos and Andalgalornis, among others.