Argentavis is a group of birds that no longer exists, found in three places in the Epecuén and Andalhualá Formations in central and northwestern Argentina. These remains are from the Late Miocene period. The main species, A. magnificens, is sometimes called the giant teratorn. Argentavis was one of the largest flying birds ever to live, and it held the record for the heaviest flying bird. However, this record was later surpassed by another bird, Pelagornis sandersi, which was described in 2014. Pelagornis sandersi is estimated to have had wings about 20% longer than those of Argentavis.
History of discovery
The first remains of Argentavis were discovered during a search by the Museo de La Plata, about 15 km south of Hidalgo station, in the Salinas Grandes de Hidalgo area of the Huayquerian Epecuén (now Cerro Azul) Formation in La Pampa Province, Argentina. Rosendo Pascual and Eduardo Tonni found the remains, which included parts of the skull, right quadrate, and sections of the legs and arms. The materials were taken to the Museo de La Plata and stored as specimen number MLP 65-VII-29-49. A copy of the specimen was made at the Los Angeles County Museum.
Kenneth Campbell Jr. and Eduardo Tonni described MLP 65-VII-29-49 in a 1980 paper and named it the holotype of the new species Argentavis magnificens. The genus name, Argentavis, comes from the Latin word "argentum" (meaning silver) and "avis" (meaning bird), referring to Argentina, where the remains were found. The species name, magnificens, means "magnificent" in Latin. The researchers noted that most of the material was severely broken, though the skull and other parts were not crushed. This damage made it hard to identify many parts of the body, but the skull and quadrate provided enough evidence to link Argentavis to the group Teratornis. This classification made it the third genus in the Teratornithidae family and the first from outside North America.
In 1995, Campbell described three additional Argentavis specimens found during a museum survey in Argentina in 1983. The first was an uncatalogued ungual phalanx (a part of a finger or toe) from the Museo Municipal de Ciencias Naturales in Mar del Plata. It was collected in 1982 from the Cerro Azul Formation, about 60 km west of the type locality near Carhué. It was assigned to Argentavis based on its size and certain bone features, which were about 1.5 times larger than those of Teratornis merriami from the La Brea Tar Pits. However, Marcos Cenizo and others later reclassified this specimen into the Phorusrhacidae family in 2012, as its features were not strong enough to confirm it belonged to Argentavis. They also found a previously unreported piece of an ungual phalanx linked to the holotype, which had different features and did not match A. magnificens.
The other specimens were found in the Andalhualá Formation of the Valle de Santa María, about 1,200 km northwest of the type locality. Radioisotope dating from 1979 placed the formation’s age at 6.02 and 6.68 million years ago, refining earlier estimates of 8–5 million years ago. These two specimens, a left coracoid (PVL 4600) and a tibiotarsus (a leg bone), were collected in 1983 and 1939, respectively, and stored at the Paleontología Vertebrados Lillo in San Miguel de Tucumán. They were smaller than the holotype and in slightly better condition, but few new bone features were identified.
Classification
Argentavis is a member of the family Teratornithidae, a group of large birds of prey that lived in the Americas from the Late Oligocene to the Late Pleistocene. This group now includes seven species across six genera. A. magnificens is the second-oldest species in the group, with Taubatornis campbelli being the oldest. The fact that the two oldest species in the group are from South America suggests that the entire group first evolved there and later moved to North America during the later part of the Cenozoic era.
Teratornithidae was studied in a 1988 analysis by Steven Emslie, which focused on skull features of birds in the order Ciconiiformes, including storks and New World vultures (Vulturidae). This study used Teratornis merriami as a representative of Teratornithidae and found the group to be closely related to Vulturidae but not part of it. Because the study identified more shared features between Vulturidae and Teratornithidae than features unique to either group, Emslie suggested that Brodkorb’s 1964 classification of teratornithids as a subfamily within Vulturidae might be more accurate than keeping them as a separate family, as Campbell and Tonni did. Today, Teratornithidae remains classified as a family.
Teratornithidae (including Argentavis)
Gymnogyps californianus
Description
The bones of the holotype of Argentavis are broken in many places, although the crushing damage is small except for the skull parts. As noted by Campbell and Tonni in 1980, the parts of the body below the skull (postcranial elements) are missing their most important features. The preserved part of the ulna has no identifying characteristics. Because of this, only the partial skull and quadrate were used to assign the bones to a new species. A partial claw (ungual phalange) found later on the holotype has not been described.
The quadrate has several key differences that help distinguish it from Teratornis. The socket for the quadratojugal bone is located farther back, and the surface where the lower jaw connects extends more toward the front and lower part but not as far forward in proportion. The area where it connects to the anteromedial part is much larger in proportion and at a smaller angle compared to the horizontal. The place where the squamosal bone connects is hemispherical, and the connection to the pterygoid bone is positioned more to the side. The shaft of the coracoid bone is flattened on the side near the humerus, with the front part of the glenoid facet nearly flat. On the inside of the glenoid facet, the shaft is curved outward. The glenoid facet itself is curved inward when viewed from the side, with the deepest point slightly below the middle. When viewed from the back, it is nearly vertical and aligned with the coracoidal fenestra, which is much closer to the procoracoid. The procoracoid is smaller, with the ridge leading to the internal distal angle being small but clearly visible.
The humerus of Argentavis has a different curve compared to Teratornis, with the top two-thirds being straighter and the front third sharply curved upward. The humeral shaft appears S-shaped when viewed from above. The deltoid crest has a noticeable knob, though the bottom part is not preserved. The shaft is slightly less curved between the deltoid and bicipital crests. The external tricipital groove seems to extend to the ectepicondylar prominence, but this part has broken off. The carpometacarpus has a deeper, more forward-facing groove on the second metacarpal, and the back half of the shaft is more rounded with a small ridge on the back side. The distal metacarpal symphysis is closer to the center of the shaft, and the front end of the facet for the second digit extends further backward at a greater angle. The third metacarpal has a more triangular shape, with a more hollow front surface and a pronounced ridge.
The tibiotarsus differs from Teratornis by being slightly curved when viewed from the front, though this might be due to breakage, and by having an underdeveloped fibular crest. The beginning of the tendinal groove is more symmetrical and closer to the center of the shaft. The internal ligamental prominence is longer, more noticeable, and located closer to the top compared to T. merriami.
In 1980, Campbell and Tonni estimated the wingspan of Argentavis to be between 6.5 to 7.5 meters (21 ft 4 in to 24 ft 7 in) by comparing it to Teratornis merriami. In their 1983 study, the same authors estimated the wingspan by scaling up the size of the California condor, with the highest estimate being 8.3 meters (27 ft 3 in) and other estimates between 5.7 to 6.4 meters (18 ft 8 in to 21 ft 0 in). In their 2024 paper, Gayford and colleagues considered the 8.3-meter estimate to be an outlier. In 2010, Mayr and Rubilar-Rogers estimated the wing skeleton length of Argentavis and Pelagornis chilensis at 1.83 meters (6 ft 0 in) and 2.1 meters (6 ft 11 in) respectively, with P. chilensis having an estimated wingspan of 5.2 to 6.1 meters (17 ft 1 in to 20 ft 0 in). This suggests Argentavis likely had a smaller wingspan unless it had much longer primary feathers. In 2014, Daniel Ksepka estimated the wingspan of Pelagornis sandersi at 6.06 to 7.38 meters (19 ft 11 in to 24 ft 3 in), which is larger than his estimate for Argentavis (5.09 to 5.57 meters or 16 ft 8 in to 18 ft 3 in) and 5.70 to 6.07 meters (18 ft 8 in to 19 ft 11 in) based on comparisons with the California condor. For comparison, the living bird with the largest wingspan is the wandering albatross, reaching up to 3.5 meters (11 ft 6 in).
In 1980, Campbell and Tonni estimated the body mass of Argentavis to be 120 kg (265 lb), while their 1983 paper estimated it at about 80 kg (176 lb). Later studies suggested a lower estimate of 70 to 72 kg (154 to 159 lb). Argentavis still holds the title of the heaviest known flying bird, with P. sandersi estimated to weigh no more than 21.9 to 40.1 kg (48 to 88 lb). Since A. magnificens lived in terrestrial environments, a useful comparison is the Andean condor, the largest living flighted land bird in both wingspan and weight. The Andean condor has an average wingspan of 2.82 meters (9 ft 3 in) and can weigh up to 15 kg (33 lb). New World vultures, like the condor, are considered the closest living relatives to Argentavis and other teratorns. The average weights of the wandering albatross and Andean condor are much lower than Argentavis, at about 8.5 kg (19 lb) and 11.3 kg (25 lb) respectively.
As a general rule, a wing loading of 25 kg/m² is considered the limit for avian flight. Estimates for Argentavis include
Paleobiology
Argentavis likely laid one or two eggs, each weighing about 1 kilogram (2.2 pounds), every two years. Climate conditions suggest that the birds may have incubated their eggs during the winter, with each parent taking turns to sit on the eggs and find food every few days. The young birds probably became independent after about 16 months but did not reach full maturity until they were around twelve years old. To keep the population stable, no more than 2% of the birds could have died each year. Because of its large size and ability to fly, Argentavis faced little predation, and most deaths in adults were likely due to old age or disease.
Based on the size and shape of its wings, scientists believe that A. magnificens mainly flew by soaring, using flapping flight only for short periods. Evidence from its bones suggests that its breast muscles were not strong enough for long periods of flapping. Studies of condor flight show that Argentavis could fly effectively in normal conditions, as large soaring birds typically flap their wings only briefly.
Although its legs were strong enough for running or jumping, its long wings made it difficult to flap until it gained height. This means Argentavis probably relied on wind to take off. It may have used mountain slopes and headwinds to launch itself, and could have taken off easily even from gently sloped ground. Argentavis likely lived and flew similarly to modern Andean condors, searching large areas for dead animals. It probably used rising warm air, called thermal currents, to stay in the sky. Scientists estimate that the minimum speed needed for A. magnificens to fly was about 11 meters per second (36 feet per second) or 40 kilometers per hour (25 miles per hour). The climate in the Andean foothills of Argentina during the late Miocene was warmer and drier than today, which would have helped Argentavis stay aloft using thermal updrafts.
Argentavis likely had territories larger than 500 square kilometers (190 square miles), searching these areas for food. The birds may have flown in a north-to-south pattern to avoid strong winds. This species appears less suited for hunting than its relatives and probably preferred to scavenge for dead animals. Argentavis may have used its large size and wings to scare metatherian mammals and small phorusrhacids away from their kills. Phorusrhacids were the largest land predators in Miocene South America, and the largest species that lived alongside Argentavis, Devincenzia, weighed up to 350 kilograms (772 pounds). Scientists Torres Etchegorry & Degrange (2024) suggested that Argentavis may have scavenged or stolen food from others, based on brain structure studies.