Argentavis magnificens was among the largest flying birds ever to exist, quite possibly surpassed in wingspan only by Pelagornis sandersi, which was described in 2014. A. magnificens, sometimes called the giant teratorn, is an extinct species known from three sites in the Epecuén and Andalhualá Formations in central and northwestern Argentina dating to the Late Miocene (Huayquerian), where a good sample of fossils has been obtained.
A North American team has studied the flight abilities of Argentavis magnificens, which lived six million years ago in Argentina.
The largest bird known to have taken to the skies would have been a remarkable glider, scientists say.
With its seven-metre (23ft) wingspan, the animal must have been an expert at riding thermals and updrafts. 
- Argentavis at Fossilworks.org
- Ancient American bird was glider. BBC, 2007-JUL-02. Retrieved 2008-JAN-14