Monster birds with wingspans that stretched up to 21 feet (6.4 meters) long, which is about as long as a U-Haul truck, flew above the clouds in Antarctica about 50 million years ago, a new study finds.

The very large species called pelagornithids arose 15 million years after an asteroid was said to have wiped the population of non-avian dinosaurs. The study, which was published in the journal Scientific Reports, studied the bone from a bird’s foot collected on Seymour Island near the Antarctic Peninsula in the 1980s.

It was Peter Kloess, a paleontology graduate student from University of California, Berkley, found the bone in 2015, among the collections of the University of California Museum of Paleontology. He found out that the bones were from an older rock, instead of what the label said to be 40 million years old, it was in fact, 50 million years old and far larger than the pelagornithid bones found during that age.

“I love going to collections and just finding treasures there,” Kloess said in a statement. “Somebody has called me a museum rat, and I take that as a badge of honor. I love scurrying around, finding things that people overlook.”

Kloess and his colleagues found another bone from the same island and era. Analyzing it, they found the skull to be 60 meters long, which might be the biggest pelagornithid ever found.