Imagine an albatross with a hacksaw for a mouth. Set that strange creature about 50 million years in the past and you’ve got the image of a pelagornithid, a group of ancient avians that included some of the largest flying birds of all time. And now paleontologists have uncovered in that group what may be the largest known flying birds ever, with wingspans of roughly 20 feet.
The new study documenting the birds, published today in Scientific Reports, is the result of a fossil detective story spanning from Antarctica to California. By comparing a pair of polar fossils to the remains of related birds, paleontologists have been able to identify the early history of enormous fliers that were some of the first birds capable of soaring across seas.
During the 1980s, University of California Berkeley paleontologist Peter Kloess says, scientists searching for Antarctic fossils found some delicate bird bones—a jaw and part of a foot from an ancient bird—on Seymour Island. Those bones then made a long journey to California, but their story was only just starting.
The jaw and foot bone were just two of a huge collection kept at the University of California Riverside. In 2003, however, the 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. And they stood out. “Bony-toothed jaws are rare in the vertebrate record,” senior museum scientist Pat Holroyd says. “When you see one, you remember it and mentally file it away for later.”
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, also known as bony-toothed birds that have a very long fossil record. The oldest pelagornithids evolved about 56 million years ago, and the most recent flew through the skies about two million years ago. Their fossils are found all over the world.
When Kloess visited the University of California Museum of Paleontology to pore over the collections, Holroyd pointed out the bird’s jaw bone. The jaw seemed interesting enough for its rarity, but there was much more to the story. “I started this research project thinking it would be a short descriptive paper on a jaw fragment to add to the knowledge of a cool group of birds,” Kloess says, adding, “I had no idea that it would represent a giant individual.”
Researching the jaw set Kloess and colleagues looking for additional bony-toothed bird bones in the museum collections. The researchers were in luck. In addition to the jaw, the collection included a foot bone—technically called a tarsometatasus—from another Antarctic pelagnornithid. The bone came from another large individual, but its real importance was in its age. A different researcher who previously studied the foot bone labeled it as belonging a rock unit called the Submeseta Formation, which is between 43 and 35 million years old, but by looking over where the fossil was found the researchers reassigned it to a rock layer in the La Meseta Formation, about 50 million years old. This falls within a time called the Eocene, when life had recovered from the asteroid-induced mass extinction and was thriving again. Together, the foot bone and the jaw indicate that large bony-toothed birds thrived in the Antarctic for millions of years.
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. The next closet fossil contender is an extinct vulture relative called Argentavis, which had a wingspan between 16 and 20 feet. The close competition might be a signal that these birds were pushing the boundaries of flight. Previous studies have calculated that the largest of the bony-toothed birds were near the limit of how big a bird could get and still fly, meaning these birds are the strongest contenders for the largest flying birds to ever soar.
And matched with the new data on the age of the fossils, Kloess says, “we can say that giant pelagornithids appeared earlier than previously known and that Antarctica saw a range of pelagornithid sizes from the early to late Eocene.” Small to large, bony-toothed birds were an important part of ancient Antarctic ecosystems.
Those impressive wings would have allowed the pelagornithids to range far and wide, soaring long distances on outstretched wings. That helps explain why fossils from various species of pelagornithids have been found all over the world during their extended evolutionary tenure. These long-lived and successful birds likely using their spiky jaws to feed on fish and squid snatched from just beneath the surface.
In the case of the birds described in the new study, the avians lived in an environment that would have seemed strange in some ways and familiar in others. “Eocene Antarctica was much warmer than we see today,” Kloess says, with carpets of ferns and stands of conifers on land that sheltered prehistoric marsupials and even frogs. Some of the other birds might have seemed familiar, though. Ancient relatives of penguins, albatrosses, and falcons have been found from these rocks, with the bony-toothed birds adding to the flock.
Naturally, the existence of these big birds raises the question of whether there might be larger fliers out there, especially because fossils of the ancient seabirds are so rare. “It’s hard to know if we have yet found the largest pelagornithids,” Holroyd says.