Sometimes finding a skeleton in a closet can be a good thing – if you’re a paleontologist. Meet Pelagornis sandersi, a giant bird with a wingspan 21 feet across – so wide that it could have been the size of a (very) small plane.

The enormous extinct avian, described in the Proceedings of the National Academy of Sciences, pushes the limit of what’s possible in bird flight.

The one and only known Pelagornis sandersi fossil’s wings stretch a whopping 20.99 feet — about twice that of the royal albatross, among the largest living birds capable of taking to the skies. It sported strange tooth-like cones that protruded from its beak.

The remarkable bones were actually discovered in 1983 near Charleston Airport in South Carolina, but they remained hidden in a drawer at the Charleston Museum until study author Daniel Ksepka, a paleontologist then at North Carolina State University in Raleigh, came across them about three decades later.

“I was not expecting this bird when I went down there,” said Ksepka, now at the Bruce Museum in Connecticut. Ksepka named the strange specimen after Albert Sanders, the now-retired curator who collected the unique fossil after it was discovered – and who later invited Ksepka to come look through fossils at the museum.

P. sandersi, which lived 25 million to 28 million years ago, was probably larger even than another extinct mega-bird, Argentavis magnificens, Ksepka said. Some have previously estimated that Argentavis’ wingspan was nearly 7 meters, but Ksepka said with the data in hand, Pelagornis still wins: Argentavis would have had a size range of 5.09 to 6.07 meters and Pelagornis would have been about a meter longer, at 6.06 to 7.38 meters. (Argentavis was probably more massive, however.)

Birds come in all sizes – and some species that have cropped up over the last 150 million years have been a thousand times larger than their brethren.