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Argentavis

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Argentavis
Temporal range: Late Miocene (Huayquerian)
~9.0–6.8 Ma
↓
Life reconstruction of a grounded individual
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Cathartiformes
Family: †Teratornithidae
Genus: †Argentavis
Campbell & Tonni 1980
Species:
†A. magnificens
Binomial name
†Argentavis magnificens
Campbell & Tonni 1980

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]

Description

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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.[3] 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.[citation needed]

Size

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A comparison of Argentavis with (left to right) a human, a giant Miocene penguin, an emperor penguin, an elephant bird, an ostrich and an Andean condor. The estimated weight and wingspan of Argentavis as stated have since been reduced.

Estimates for Argentavis' wingspan vary widely depending on the method used for scaling, i.e. regression analyses or comparisons with the California condor. At one time, published wingspans for the species measured up to 7.5 to 8 m (24 ft 7 in to 26 ft 3 in) in width, but more recent estimates put the wingspan within the range of 5.09 to 6.5 m (16 ft 8 in to 21 ft 4 in). Recent studies present doubts on the wingspan of the species reaching or exceeding 7 m (23 ft 0 in).[4][5] At the time of description, Argentavis was the largest flying bird known to have existed but it has since been exceeded by another extinct species, Pelagornis sandersi, in wingspan, which the 2014 description estimated at 7 to 7.4 m (23 ft 0 in to 24 ft 3 in).[6][7] For comparison, the living bird with the largest wingspan is the wandering albatross, averaging 3 m (9 ft 10 in) and spanning up to 3.7 m (12 ft 2 in). When grounded, Argentavis' height has been estimated at 1.5 to 1.8 m (4 ft 11 in to 5 ft 11 in), roughly equivalent to that of an adult human. Furthermore, its total length (from bill tip to tail tip) was approximately 3.5 m (11 ft 6 in).[8]

Prior publications estimated the body mass of Argentavis at 80 kg (180 lb), but more refined techniques show a more typical mass would likely have been somewhere between 70 to 72 kg (154 to 159 lb), although weights could have varied depending on conditions.[4][8][9] 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 22 to 40 kg (49 to 88 lb).[6] 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 3.3 m (10 ft 10 in) with an average of around 2.82 m (9 ft 3 in), and the latter reaching a maximum of up to 15 kg (33 lb). 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 8.5 kg (19 lb) and 11.3 kg (25 lb), respectively.[10][11]

As a rule of thumb, a wing loading of 25 kg/m2 is considered the limit for avian flight.[12] A number of estimates related to wing loading have been produced for Argentavis, most notably the wing area, estimated at 8.11 m2 (87.3 sq ft), and the wing loading, estimated at 84.6 N/m2 (1.77 lb/ft2).[5] The heaviest extant flying birds are known to weigh up to a maximum of 21 kg (46 lb) (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 23 kg (51 lb).[11] Meanwhile, the sarus crane is the tallest flying bird alive, at up to 1.8 m (5 ft 11 in) tall, standing about as high as Argentavis due to its long legs and neck.[citation needed]

Paleobiology

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Life history

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Comparison with extant birds suggests Argentavis laid one or two eggs with a mass of around 1 kg (2.2 lb) 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 untill 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.[13]

Flight

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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 for to enable flapping of the wings for extended periods.[14] 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.[15]

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.[3] 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 11 metres per second (36 ft/s) or 40 kilometres per hour (25 mph).[16] 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.[citation needed]

Food

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Argentavis' territories probably measured more than 500 square kilometres (190 sq mi), 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.[13][17] 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 350 kilograms (770 lb).[18]

Unlike extant condors and vultures, teratorns generally had long, eagle-like beaks and are believed to have been active predators. This is seemingly true of Argentavis, although other teratorns are likely to have been more active, considering the substantial size differences. Argentavis may have ambushed small prey like rodents, armadillos and the young of larger animals such as ground sloths. The species would've required about 2.5 to 5 kg (5.5 to 11.0 lb) of meat each day.[13][19] When hunting, Argentavis may have lain in wait from a ground position. The skull structure of Argentavis suggests that it ate most of its prey whole, rather than tearing off pieces of flesh.[3][13]

References

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  1. ^ Argentavis at Fossilworks.org
  2. ^ Ancient American bird was glider. BBC, 2007-JUL-02. Retrieved 2008-JAN-14
  3. ^ a b c Campbell, Kenneth E. Jr.; Tonni, E. P. (1983). "Size and locomotion in teratorns" (PDF). Auk. 100 (2): 390–403. doi:10.1093/auk/100.2.390.
  4. ^ a b Alexander, David E. (24 July 2007). "Ancient Argentavis soars again". Proceedings of the National Academy of Sciences of the United States of America. 104 (30): 12233–12234. Bibcode:2007PNAS..10412233A. doi:10.1073/pnas.0705515104. PMC 1941455. PMID 17640902.
  5. ^ a b Chatterjee, S.; Templin, R. J.; Campbell, K. E. (2007-07-24). "The aerodynamics of Argentavis, the world's largest flying bird from the Miocene of Argentina". Proceedings of the National Academy of Sciences of the United States of America. 104 (30): 12398–12403. Bibcode:2007PNAS..10412398C. doi:10.1073/pnas.0702040104. PMC 1906724. PMID 17609382.
  6. ^ a b Ksepka, Daniel T. (22 July 2014). "Flight performance of the largest volant bird". Proceedings of the National Academy of Sciences of the United States of America. 111 (29): 10624–10629. Bibcode:2014PNAS..11110624K. doi:10.1073/pnas.1320297111. PMC 4115518. PMID 25002475.
  7. ^ Vergano, Dan (8 July 2014). "Biggest Flying Seabird Had 21-Foot Wingspan, Scientists Say". National Geographic. Archived from the original on July 8, 2014. Retrieved 8 July 2014.
  8. ^ a b VIZCAÍNO, SERGIO F.; FARIÑA, RICHARD A. (29 March 2007). "On the ftight capabilities and distribution of the giant Miocene bird Argentavis magnificens (Teratornithidae)". Lethaia. 32 (4): 271–278. doi:10.1111/j.1502-3931.1999.tb00546.x.
  9. ^ Campbell Jr, K. E., & Marcus, L. (1992). The relationship of hindlimb bone dimensions to body weight in birds. Natural History Museum of Los Angeles County Science Series, 36, 395-412.
  10. ^ Dunning, John B. Jr., ed. (2008). CRC Handbook of Avian Body Masses (2nd ed.). CRC Press. ISBN 978-1-4200-6444-5.
  11. ^ a b Wood, Gerald (1983). The Guinness Book of Animal Facts and Feats. Enfield, Middlesex : Guinness Superlatives. ISBN 978-0-85112-235-9.
  12. ^ Meunier, K. (1951). "Korrelation und Umkonstruktionen in den Größenbeziehungen zwischen Vogelflügel und Vogelkörper" [Correlation and restructuring in the size relationship between avian wing and avian body]. Biologia Generalis (in German). 19: 403–443.
  13. ^ a b c d Palmqvist, Paul; Vizcaíno, Sergio F. (2003). "Ecological and reproductive constraints of body size in the gigantic Argentavis magnificens (Aves, Theratornithidae) from the Miocene of Argentina" (PDF). Ameghiniana. 40 (3): 379–385.
  14. ^ Yong, Ed (2007-07-08) Argentavis, the largest flying bird, was a master glider. notexactlyrocketscience.wordpress.com
  15. ^ Williams, H. J.; Shepard, E. L. C.; Holton, Mark D.; Alarcón, P. A. E.; Wilson, R. P.; Lambertucci, S. A. (13 July 2020). "Physical limits of flight performance in the heaviest soaring bird". Proceedings of the National Academy of Sciences. 117 (30): 17884–17890. Bibcode:2020PNAS..11717884W. doi:10.1073/pnas.1907360117. PMC 7395523. PMID 32661147.
  16. ^ Vizcaíno, Sergio F.; Palmqvist, Paul; Fariña, Richard A. (2000). "¿Hay un límite para el tamaño corporal en las aves voladoras?" [Is there a limit to body size in flying birds?]. Encuentros en la Biología (in Spanish). 64. Archived from the original on 2001-05-13.
  17. ^ Tambussi, Claudia P. (June 2011). "Palaeoenvironmental and faunal inferences based on the avian fossil record of Patagonia and Pampa: what works and what does not". Biological Journal of the Linnean Society. 103 (2): 458–474. doi:10.1111/j.1095-8312.2011.01658.x. hdl:11336/53447.
  18. ^ Blanco, Rudemar Ernesto; Jones, Washington W (2005). "Terror birds on the run: a mechanical model to estimate its maximum running speed". Proceedings of the Royal Society B: Biological Sciences. 272 (1574): 1769–1773. doi:10.1098/rspb.2005.3133. PMC 1559870. PMID 16096087.
  19. ^ Croft, D. A. (2016). Horned armadillos and rafting monkeys: the fascinating fossil mammals of South America. Indiana University Press.[page needed]

Further reading

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