There have been many big birds in the history of life, from the 10-foot-high flightless elephant birds of Madagascar to the carnivorous, earth-bound, 9-foot-tall Brontornis of prehistoric Patagonia. But the roughly 6-million-year-old Argentavis magnificens was special. With a wingspan of 23 feet, this was the largest flying bird of all time. Exactly how such a large bird took off is a matter of debate, but its anatomy indicates that it was primarily a glider, like modern vultures and condors. Unless there is an even larger fossil bird out there, Argentavis may represent the upper limit for how big birds could get without sacrificing the power of flight.