Argentavis magnificens is the largest flying bird ever discovered.
This bird, sometimes called the Giant Teratorn, is an extinct species known (as of 2006) from 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.
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. 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.
Currently accepted estimates:
Wingspan: 5.8–8 m (19 – 26 ft)
Wing area: nearly 7 m² (75 square ft)
Wing loading: c. 11.5 kg/m²
Length: 3.5 m (11.5 ft)
Height: 1.7–2 m (5.6–6.5 ft)
Weight: 60–80 kg (140–180 lb)
For comparison, the living bird with the largest wingspan is the Wandering Albatross (3.63 m). Since A. magnificens is known to have been a land bird, another good point of comparison is the Andean Condor, which is not too distantly related to Argentavis. This bird is among the largest land birds, with a wingspan of about 3 m and weighing up to 12 kg.
The ability to fly is not a simple question of weight, except in extreme cases. Size and structure of the wing must also be taken into account. As a rule of thumb, a wing loading of 25 kg/m² is considered the limit for avian flight.
The heaviest extant flying bird is not heavier than 20 kg (there are several contenders, among which are the European Great Bustard and the African Kori Bustard). 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 are a group of pterosaurs named azhdarchids, extinct flying animals that existed during the age of the dinosaurs and died out at the end of the Cretaceous. Estimations of the wingspan of the largest species like Quetzalcoatlus and Hatzegopteryx exceeds 10 m, with less conservative estimates being 12 m or more.