Researchers from California and China identified the 50-million-year-old bone of a giant bird that lived in Antarctica. Paleontologists have uncovered a bird in the pelagornithid group that may be the largest known flying birds ever, with wingspans of roughly 20 feet. By comparing a pair of polar fossils to the remains of related birds, paleontologists have been able to identify the early history of these enormous fliers that were some of the first birds capable of soaring across seas. The jaw and foot bone were just two of a huge collection kept at the University of California Riverside. In 2003, however, more than 10,000 fossils of the Riverside collection were transferred to the University of California Museum of Paleontology at the Berkeley campus, the bird bones among them. The bird jaw, which came from a rock formation laid down over 37 million years ago, looks almost like a woodcutting tool rather than a bone. The jaw has a series of large and small spikes, outgrowths of the beak that have a passing resemblance to teeth. On a living animal, the points would have been covered in keratin and given the bird a sinister saw-toothed smile. That feature immediately identified the jaw as belonging to a pelagornithid, these birds that have a very long fossil record. Paleontologists have found bony-toothed birds from places all over the world, from New Zealand to South Carolina. The newly-described Antarctic fossils, though, are the oldest known and hint that these birds quickly diversified into a range of sizes within six million years of their origin. By 50 million years ago, there were bony-toothed birds from the size of a modern-day albatross to giants with wingspans twice as wide.