Argentavis is an extinct genus of teratornithid known from three sites in the Epecuén and Andalhualá Formations in central and northwestern Argentina dating to the Late Miocene (Huayquerian). The type species, A. magnificens, is sometimes called the giant teratorn. Argentavis was among the largest flying birds to ever exist, holding the record for heaviest flying bird, although it was surpassed in wingspan after the 2014 description of Pelagornis sandersi, which is estimated to have possessed wings some 20% longer than those of Argentavis.

History of discovery

The first remains of Argentavis were found during an expedition by the Museo de La Plata, roughly 15 km south of Hidalgo station, at the Salinas Grandes de Hidalgo locality in the Huayquerian Epecuén (now Cerro Azul) Formation of La Pampa Province, Argentina, by Rosendo Pascual and Eduardo Tonni. This material consisted of an associated partial skeleton with portions of the skull, right quadrate and parts of the legs and arms. The material was then brought to the Museo de La Plata and housed under specimen number MLP 65-VII-29-49. It was cast at the Los Angeles County Museum.

Kenneth Campbell Jr. and Eduardo Tonni would go on to describe MLP 65-VII-29-49 in a 1980 paper and designated it as the holotype specimen of the new taxon Argentavis magnificens. The generic name Argentavis comes from the Latin "argentum", meaning silver, and "avis", meaning bird, and was used in reference to Argentina, the country where the remains of the animal were found. The specific name magnificens comes from the same word in Latin, meaning magnificent. They note that all the material has been severely fractured, although most of the material except for the skull was not severely crushed. This fracturing, among other sustained damages, meant that most of the postcranial skeleton lacked its diagnostic portions. However, the skull and quadrate provided strong enough evidence of Argentavis relation to Teratornis, and permitted Campbell and Tonni to describe it as a teratornithid. This made it the third described genus in this family and the first from outside North America. Marcos Cenizo and colleagues would revisit this element in 2012 and refer it to the family Phorusrhacidae instead, based on the fact that the provided characters were too poor to confirm an assignment to Argentavis. Cenizo and colleagues also mention a previously unreported proximal fragment of an ungual phalanx which was found associated with the holotype during further study. This element lacked both distinctive features of Campbell's 1995 element and possessed numerous others, confirming that it does not belong to A. magnificens. This confirmed and refined the earlier Huayquerian (8-5 mya) estimate given by Campbell and Tonni in 1980. Both of these specimens are housed in the collections of the Paleontología Vertebrados Lillo in San Miguel de Tucumán. The first, a left coracoid (PVL 4600), was collected by G. Bossi in March of 1983. These specimens were said to be smaller than the equivalent material in the holotype specimen and to have been in slightly better condition, although few new osteological characters could be differentiated. A. magnificens is the second-oldest of these taxa, surpassed only by Taubatornis campbelli. The fact that both of the oldest taxa in the group originate from South America suggests that the group as a whole also evolved here, only migrating to North America in the latter part of the Cenozoic.

Teratornithidae was included in a phylogenetic analysis that was published by Steven Emslie in 1988, reproduced below. The analysis was conducted using cranial characters of various taxa within the order Ciconiiformes, the storks, with a specific focus on Vulturidae (Cathartidae, New World vultures). This analysis included Teratornis merriami as a representative of Teratornithidae, and found the group to be just outside of Vulturidae.

Description

thumb|left|[[Life reconstruction of a grounded individual]]

The bones of the holotype of Argentavis are severely fractured, although crushing is minimal aside from the preserved skull elements. As noted by Campbell and Tonni in 1980, the postcranial elements all lack their most diagnostic portions, with the preserved portion of the ulna having no diagnostic characters at all. Because of this, only the partial skull and quadrate allowed the assignment to a (new) species. In 2010, Mayr and Rubilar-Rogers estimated the wing skeleton length of Argentavis and Pelagornis chilensis at and respectively, with P. chilensis having an estimated wingspan of , suggesting that Argentavis probably had a smaller wingspan unless it had much longer primary feathers. In his 2014 description of Pelagornis sandersi, Daniel Ksepka estimated the wingspan of P. sandersi at , exceeding that of Argentavis which he estimated at and based on regression analyses and comparisons with the California condor respectively. For comparison, the living bird with the largest wingspan is the wandering albatross, reaching upwards of .

The initial description by Campbell and Tonni in 1980 tentatively estimated the body mass of Argentavis at , Argentavis still retains the title of the heaviest known flying bird by a considerable margin, with the aforementioned P. sandersi being estimated to have weighed no more than .

As a rule of thumb, a wing loading of 25&nbsp;kg/m<sup>2</sup> is considered the limit for avian flight. Studies on condor flight indicate that Argentavis was fully capable of flight in normal conditions, as modern large soaring birds spend very little time flapping their wings regardless of environment.

Although its legs were strong enough to provide it with a running or jumping start, the wings were simply too long to flap effectively until the bird had gained some vertical distance, meaning that, especially for takeoff, Argentavis would have depended on the wind. Torres Etchegorry & Degrange (2024) suggested that Argentavis was a scavenger or even a kleptoparasitic bird, living in open areas without much vegetation, based on its probable brain morphology inferred from endocast reconstruction.

References

Further reading

  • Wellnhofer, Peter (1996): The Illustrated Encyclopedia of Pterosaurs. Barnes and Noble Books, New York.
  • Argentavis information Website about the Argentavis magnificens
  • BBC News: Ancient American bird was glider – BBC News article
  • How the dinosaur bird took to the skies – Daily Telegraph article
  • Secret of flight for world's largest bird revealed – COSMOS magazine article
  • Argentavis, the largest flying bird, was a master glider – Article from the blog Not Exactly Rocket Science