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.[1] [2]
In the 1970s while on an expedition by the Museo de La Plata, paleontologists Rosendo Pascual and Eduardo Tonni unearthed a fragmentary skeleton consisting of a partial skull, right coracoid, left humerus, portions of the left ulna, left radius, and left metacarpals, and shafts of the right tibiotarsus and tarsometatarsus.[3] [4] Later restudy of the specimen also found an incomplete ungual phalanx with the skeleton. These fossils had been exposed in brown-red silt and clay sediments from the Epecuén Formation in Salinas Grandes de Hidalgo in Atreucó, Argentina. These outcrops derive from the Huayquerian stage of the upper Miocene (9.0-6.8 mya). This specimen was deposited at the Museo de La Plata under catalogue number MLP 65-VII-29-49 and cast at the Los Angeles County Museum.
These fossils were described by paleontologists Kenneth Campbell Jr. and Eduardo Tonni in 1980, who named the new genus and species Argentavis magnificens with MLP 65-VII-29-49 as the holotype specimen. The generic name Argentavis is derived from the Latin root argentum, “silver”, after the country of origin, and avis, “bird”, while the specific name magnificens, “magnificent”, refers to its size. In the description, Argentavis was classified as a member of Teratornithidae and was the first described from South America. Since Argentavis
The single known humerus (upper arm bone) of Argentavis is somewhat damaged. Even so, it allows a fairly accurate estimate of its length in life. Argentavis humerus was only slightly shorter than an entire human arm. The species had stout, strong legs and large feet which indicate decent terrestrial capabilities. The bill was large, rather slender, and had a hooked tip with a wide gape.
Estimates for Argentavis'
Prior publications estimated the body mass of Argentavis at 80kg (180lb), but more refined techniques show a more typical mass would likely have been somewhere between 70and, although weights could have varied depending on conditions.[13] [14] 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 22to.[11] Since A. magnificens is known to have lived in terrestrial environments, another good point of comparison is the Andean condor, the largest extant flighted land bird both in average wingspan and weight, with the former spanning up to 3.30NaN0 with an average of around 2.820NaN0, and the latter reaching a maximum of up to 15kg (33lb). New World vultures such as the condor are thought to be the closest living relatives to Argentavis and other teratorns. Average weights are much lower in both the wandering albatross and Andean condor than in Argentavis, at approximately 8.5kg (18.7lb) and 11.3kg (24.9lb), respectively.[15] [16]
As a rule of thumb, a wing loading of 25 kg/m2 is considered the limit for avian flight. A number of estimates related to wing loading have been produced for Argentavis, most notably the wing area, estimated at 8.11m2, and the wing loading, estimated at 84.6 N/m2 (1.77 lb/ft2), or about 8.64 kg/m2. The heaviest extant flying birds are known to weigh up to a maximum of 21kg (46lb) (there are several contenders, among which are the European great bustard and the African kori bustard). An individual mute swan, which may have lost the power of flight due to extreme weight, was found to have weighed 23kg (51lb).[16] Meanwhile, the sarus crane is the tallest flying bird alive, at up to 1.80NaN0 tall, standing about as high as Argentavis due to its long legs and neck.
Comparison with extant birds suggests Argentavis laid one or two eggs with a mass of around 1kg (02lb) every two years. Climate considerations make it likely that the birds incubated during the winter, with members of a mated pair alternating between incubating and procuring food every few days. The young are thought to have been independent after some 16 months, but to not reach full maturity until they reached roughly twelve years of age. To maintain a viable population, no more than 2% of birds could have died each year. Because of its large size and ability to fly, Argentavis suffered hardly any predation, and mortality was mainly related to old age and disease in adults.
From the size and structure of its wings, it is inferred that A. magnificens flew mainly by soaring, using flapping flight only during short periods. This is further supported by skeletal evidence, which suggests that its breast muscles were not powerful enough to enable flapping of the wings for extended periods.[17] 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.[18]
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. Argentavis may have used mountain slopes and headwinds to take off, and probably could manage to do so even from gently sloped terrain with little effort. It may have flown and lived much like the modern Andean condor, scanning large areas of land for carrion. It is probable that it utilised thermal currents to stay aloft, and it has been estimated that the minimal velocity for A. magnificens is about 11m/s or 40km/h. The climate of the Andean foothills in Argentina during the late Miocene was warmer and drier than today, which would have further aided the bird in staying aloft atop thermal updrafts.
Argentavis territories probably measured more than 500km2, which the birds screened for food, possibly utilizing a north–south flying pattern to avoid being slowed by adverse winds. This species seems less aerodynamically suited for predation than its relatives and probably preferred to scavenge for carrion. Argentavis may have used its wings and size to intimidate metatherian mammals and small phorusrhacids to take over their kills.[19] Phorusrhacids were the largest land predators in Miocene South America, and probably the biggest threats that Argentavis faced, with the largest species that coexisted with Argentavis, Devincenzia, weighing up to 350kg (770lb).[20]