Argentavis

Taxobox
name = Giant Teratorn


image_width = 250px
fossil_range = Late Miocene
regnum = Animalia
phylum = Chordata
classis = Aves
ordo = Ciconiiformes
familia = †Teratornithidae
genus = "†Argentavis"
genus_authority = Campbell & Tonni, 1980
species = "†A. magnificens"
binomial = "Argentavis magnificens"
binomial_authority = Campbell & Tonni, 1980

"Argentavis magnificens" (literally "Magnificent Argentine Bird") is the largest flying bird ever discovered. This bird, sometimes called the Giant Teratorn, is an extinct species known from (as of 2006) three sites from the late Miocene (6 million years before present) of central and northwestern Argentina, where a good sample of fossils has been obtained. [ [http://news.bbc.co.uk/2/hi/science/nature/6262740.stm Ancient American bird was glider] . "BBC", 2007-JUL-02. Retrieved 2008-JAN-14]

The humerus (upper arm bone) of "Argentavis" is somewhat damaged. It allows a fairly accurate estimate of its length in life, which was a bit shorter than an entire human arm.Campbell & Tonni (1983)] The species apparently had stout, strong legs and large feet which enabled it to walk with ease. The bill was large, rather slender, had a hooked tip with a wide gape.

Physical characteristics

Currently accepted estimates:
* Wingspan: 5.8 - 8 m (19 - 26 ft)
* Wing area: nearly 7 square m (75 square ft)
* Wing loading: c.11,5 kg/square m
* Length: 3.5 m (11.5 ft)
* Height: 1.7 - 2 m (5.6 ft - 6.5 ft)
* Weight: 60 - 80 kg (140 lb - 180 lb)

For comparison, the living bird with the largest wingspan is the Wandering Albatross ("Diomedea exulans", 3.63 m). Since "A. magnificens" is known to have been a land bird, another good point of comparison is the Andean Condor, "Vultur gryphus", which is not too distantly related to "Argentavis". This bird is among the largest land-birds altogether, with a wingspan of about 3 m and weighing up to 12 kg.

Flightlessness is not a simple question of weight, except in extreme cases. Site and structure of the wing must also be taken into account. As a rule-of-thumb, a wing loading of 25 kg/square m is considered the "de facto" limit for avian flight. [Meunier (1951)]

The "heaviest" extant flying bird is not heavier than 20 kg (several contenders, among which are the European Great Bustard "Otis tarda" and the African Kori Bustard "Ardeotis kori"). The Sarus Crane is the tallest flying bird alive, standing nearly as high as "Argentavis" due to its long legs.

The largest known flying creatures ever were certain pterosaurs, extinct flying animals distantly related to the dinosaurs. In 1971, remains of "Quetzalcoatlus" were found in Texas. The largest remains are inconclusive, and may indicate an individual with a wingspan as large as 18 m (59 ft).fact|date=September 2007 Such a wingspan, however, may violate fundamental structural limits imposed on biological fliers; some scientists favor a wingspan closer to 12 m (40 ft) in light of these arguments. Before "Quetzalcoatlus", the largest known pterosaur was "Pteranodon", with individuals with 9 m (30 ft) wingspan. [Wellnhofer (1996): p.139]

Ecology

As with all extinct species, not much can be known about the Giant Teratorn's behaviour. 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. It is probable that it used thermal currents as well. It has been estimated that the minimal velocity for the wing of "A. magnificens" is about 11 m/s or 40 km/h. [Vizcaíno "et al". (2000)] Especially for takeoff, they would have depended on the wind, as although their legs were strong enough to provide them with a running or jumping start, the wings were simply too long to flap effectively until the bird was some meters off the ground. However, skeletal evidence suggests that its breast muscles were not powerful enough for wing flapping for extended periods. [ [http://notexactlyrocketscience.wordpress.com/2007/07/08/argentavis-the-largest-flying-bird-was-a-master-glider/ Argentavis, the largest flying bird, was a master glider] .] Argentavis may have used mountain slopes and headwinds to take off, and probably could manage to do so from even gently sloping terrain with little effort. It may have flown and lived much like the modern Andean condor, scanning large areas of land from aloft for carrion. 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.

This species seems not as well-suited for predation aerodynamically as its relatives. It probably preferred to scavenge for carrion, and it is likely that it habitually chased marsupial carnivores such as Thylacosmilidae from their kills. Unlike extant condors and vultures, the other species of teratorns also generally had long, eagle-like beaks and they are believed to have been active predators, being less ponderous than Argentavis. When hunting actively, "A. magnificens" would probably have swooped from high above onto their prey, which they usually would have been able to grab, kill, and swallow without landing. Skull structure suggests that it ate most of its prey whole rather than tearing off pieces of flesh.

"Argentavis"' territories measured probably more than 500 square km, which the birds screened for food, possibly utilizing a generally north-south direction to avoid being slowed by adverse winds. Comparison with extant birds suggests it laid one or two eggs with a mass of somewhat over 1 kg - somewhat smaller than an ostrich egg - every two years. Climate considerations make it likely that the birds incubated over the winter months, mates exchanging duties of incubating and procuring food every few days, and that the young were independent after some 16 months, but not fully mature until aged about a dozen years. Mortality must have been very low; to maintain a viable population less than about 2% of birds may have died each year. Of course, "Argentavis" suffered hardly any predation, and mortality was mainly from old age, accidents and disease. [Palmqvist & Vizcaíno (2003)] As a comparison, the annual mortality rate for humans ranged between about 0.22 and 3% in 2007, according to the CIA World Factbook estimate.

Footnotes

References

* (1980): A new genus of teratorn from the Huayquerian of Argentina (Aves: Teratornithidae). "Contributions in Science, Natural History Museum of Los Angeles County" 330: 59-68.
* (1983): Size and locomotion in teratorns. "Auk" 100(2): 390-403. [http://elibrary.unm.edu/sora/Auk/v100n02/DJVU/P0390-P0403.djvu DjVu fulltext] [http://elibrary.unm.edu/sora/Auk/v100n02/p0390-p0403.pdf PDF fulltext]
* (1951): Korrelation und Umkonstruktionen in den Größenbeziehungen zwischen Vogelflügel und Vogelkörper ["Correlation and restructuring in the size relationship between avian wing and avian body"] [Article in German] . "Biologia Generalis" 19: 403-443.
* (2003): Ecological and reproductive constraints of body size in the gigantic "Argentavis magnificens" (Aves, Theratornithidae) from the Miocene of Argentina. "Ameghiniana" 40(3): 379-385. [http://webpersonal.uma.es/de/ppb/Argentavis.pdf PDF fulltext]
* (1996): "The Illustrated Encyclopedia of Pterosaurs". Barnes and Noble Books, New York. ISBN 0-7607-0154-7
* (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" 64 [Article in Spanish] [http://www.ciencias.uma.es/publicaciones/encuentros/ENCUENTROS64/aves.html HTML fulltext]

External links

* [http://news.bbc.co.uk/2/hi/science/nature/6262740.stm BBC News: Ancient American bird was glider] - BBC News article
* [http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/07/03/scidino103.xml How the dinosaur bird took to the skies] - Telegraph.co.uk article
* [http://www.cosmosmagazine.com/node/1421 Secret of flight for world's largest bird revealed] - COSMOS Magazine article
* [http://notexactlyrocketscience.wordpress.com/2007/07/08/argentavis-the-largest-flying-bird-was-a-master-glider/ Argentavis, the largest flying bird, was a master glider] - Article from the blog "Not Exactly Rocket Science"