In 1931, a very large distal right tarsometatarsus associated with an ungual phalanx from digit II, was described by the Uruguayan Paleontologist Lucas Kraglievich as a new species of Phororhacos (a misspelling of Phorusrhacos), P. pozzi and deposited at the Museo Argentino de Ciencias Naturales Bernardino Rivadavia in Buenos Aires, Argentina under specimen numbers MACN-6554 and 6681.

[3][4] The fossils had been found in Lower Pliocene rock layers at El Brete in Cordoba, Argentina, specifically from the Mesopotamian.

[4] Later in the same paper, Kraglievich named a subspecies of Phororhacos (Phorusrhacos) longissimus mendocinus based on a partial proximal right femur from the Late Miocene Huayquerías Formation in Mendoza, Argentina.

[5][3] Although they are sometimes considered distinct,[5] Herculano Alvarenga and Elizabeth Höfling synonymized the two species in 2013 in their reassessment of Phorusrhacidae and moved P. pozzi to Devincenzia in the same paper.

[6] The fossils were sent to the Museo de la Plata, where they were described by Angelo Cabrera in 1939, naming the Phorusrhacid specimens (MLP 37-III-7-8) Onactornis depressus.

[7] P. pozzi and P. longissimus mendocinus were moved to Onactornis by Pierce Brodkorb, who also believed that Devincenzia gallinali was a synonym of Brontornis.

[3] It probably resembled its relatives Phorusrhacos and Kelenken, like them, it was equipped with a narrow body, conspicuously elongated walking legs, and retracted wings.

[6][4] Of the few surviving elements of the body skeleton, a complete tibiotarsus from the Early Pleistocene of Uruguay (Raigón Formation) possibly referable to Devincenzia remained,[3] and it was 72 cm long and 10.4 cm wide at the lower end of the joint, resembling that of Phorusrhacos in its long and slender build, although it was larger.

[3] They were flightless, as evidenced by the proportional size of their wings and body mass, and wing-size was more reduced in larger members of the group.

They pointed out that the narrowing of the pelvis, upper maxilla, and thorax may have been adaptations for hunting in regions with high vegetation, which would permit greater agility when moving between vertical obstacles.

[3] A 2010 study by Degrange and colleagues of Andalgalornis, based on Finite Element Analysis using CT scans, estimated its bite force and stress distribution in its skull, and showed that it had lost a large degree of intracranial immobility (mobility of skull bones in relation to each other), as was also the case for other large phorusrhacids.

Due to the relative weakness of the skull at the sides and middle, these researchers considered it unlikely that Andalgalornis engaged in potentially risky behavior that involved using its beak to subdue large, struggling prey.

[12] Due to the fragmentary nature of Devincenzia fossils and the internal taxonomy of the genus being in a flux, its classification within Phorusrhacidae frequently changes.

[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 Devincenzia as a member of a large clade that includes Physornis, Phorusrhacos and Andalgalornis, among others.

After the extinction of the non-bird dinosaurs, during the early Cenozoic, mammals underwent an evolutionary diversification, and birds around the world developed a tendency towards gigantism; this includes the Gastornithidae, the Dromornithidae, the Palaeognathae, and the Phorusrhacidae.

It is unclear where the group originated; both cariamids and phorusrhacids may have arisen in South America, or arrived from elsewhere when southern continents were closer together or when sea levels were lower, and they may also have made reverse movements.

[3] Some fossils have been unearthed from the Ituzaingo Formation of Mesopotamia, Argentina, which preserves vast tidal flats similar to those in the modern day Amazon and a warm climate.

[27][28] At the Campo de Robilotte locality on Lake Epecuén near Buenos Aires, Argentina, in the Cerro Azul Formation, several fossil mammals were uncovered alongside the holotype of Onactornis depressus, a synonym of Devincenzia, in 1936 and many were described by Angelo Cabrera as new fossil species and even some genera, though few remain valid.