Argentavis

Argentavis is an extinct genus of teratornithid birds, known from three sites in the Epecuén and Andalhualá Formations of central and northwestern Argentina. These fossils date to the Late Miocene (Huayquerian). The only recognized species is A. magnificens, often called the giant teratorn. It ranks among the largest flying birds ever known, with a wingspan surpassed only by Pelagornis sandersi, though it remains the heaviest flying bird, weighing up to a certain amount.

The first fossils were collected by an expedition from the Museo de La Plata, about 15 km south of Hidalgo station, at the Salinas Grandes de Hidalgo locality in La Pampa Province. Rosendo Pascual and Eduardo Tonni recovered a partial skeleton including parts of the skull, right quadrate, and limb bones. This material, cataloged as MLP 65-VII-29-49, was brought to the Museo de La Plata and later cast at the Los Angeles County Museum. In a 1980 paper, Kenneth Campbell Jr. and Eduardo Tonni described it as the holotype of a new taxon, Argentavis magnificens. The genus name combines Latin "argentum" (silver) and "avis" (bird), referencing Argentina; the species name "magnificens" means magnificent in Latin. The authors noted that all material was severely fractured, though most postcranial bones were not crushed. The skull and quadrate, however, provided clear evidence linking Argentavis to Teratornis, allowing its classification as a teratornithid. This made it the third described genus in the family and the first from outside North America.

In a 1995 paper, Campbell described three additional specimens. The first, an uncatalogued ungual phalanx, was found in the collections of the Museo Municipal de Ciencias Naturales in Mar del Plata. It had been collected in March 1982 by Galilio Scaglia from the Cerro Azul Formation, about 60 km west of the type locality near Carhué. Campbell referred it to Argentavis based on the flexor muscle attachment site, a prominent groove on the bone’s lateral and medial surfaces, and its size—roughly 1.5 times that of the largest ungual phalanges of Teratornis merriami from the La Brea Tar Pits. In 2012, Marcos Cenizo and colleagues reassigned this element to the family Phorusrhacidae, arguing the characters were too weak to confirm an Argentavis identification. They also reported a previously unrecorded proximal fragment of an ungual phalanx found with the holotype; this fragment lacked the distinctive features of Campbell’s 1995 specimen and showed others, confirming it does not belong to A. magnificens.

The other two specimens came from the Andalhualá Formation in the Valle de Santa María, about 1200 km northwest of the type locality. Radioisotope dates from a 1979 publication by Marshall and colleagues gave ages of 6.02 and 6.68 million years, refining the earlier Huayquerian estimate (8–5 mya). Both specimens are housed at the Paleontología Vertebrados Lillo in San Miguel de Tucumán. The first, a left coracoid (PVL 4600), was collected by G. Bossi in March 1983. The second, a tibiotarsus, was recovered by L. Peirano in October 1939. These specimens are smaller than the equivalent bones in the holotype and in slightly better condition, though few new osteological features could be identified.

Argentavis belongs to the family Teratornithidae, a group of large birds of prey that lived in the Americas from the Late Oligocene to the Late Pleistocene. The family currently includes seven species across six genera. A. magnificens is the second-oldest taxon, after Taubatornis campbelli. Because the two oldest teratornithids both come from South America, the group likely evolved there, migrating to North America later in the Cenozoic.

Teratornithidae was included in a phylogenetic analysis published by Steven Emslie in 1988, using cranial characters from various taxa within the order Ciconiiformes (storks), with a focus on Vulturidae (New World vultures). The analysis included Teratornis merriami as a representative of Teratornithidae and placed the group just outside Vulturidae. Emslie noted that the analysis found more shared characters distinguishing Vulturidae and Teratornithidae from other Ciconiiformes than characters specific to either group, suggesting a close relationship. He proposed that Brodkorb’s 1964 placement of teratornithids as a subfamily within Vulturidae might be more appropriate than retaining familial rank, as Campbell and Tonni had done. Currently, Teratornithidae remains at the familial rank.

The bones of the holotype are severely fractured, though crushing is minimal except in the skull. As noted by Campbell and Tonni, the postcranial skeleton mostly lacks diagnostic portions due to fracturing and other damage.