Fossils unearthed at a construction project in South Carolina belong to a bird with the largest wingspan ever known, according to a new study. The animal measured 6.4 meters from wingtip to wingtip, about the length of a 10-passenger limousine and approaching twice the size of the wandering albatross, today’s wingspan record-holder. Like modern-day albatrosses, the newly described species would have been a soaring champ.
Fragmentary fossils of the new species—bones from a fairly complete skull, as well as some from one wing and leg—were discovered in 1983, when excavations began for a new terminal at Charleston International Airport. The fossils had been entombed in rocks laid down as seafloor sediments sometime between 25 million and 28 million years ago, says Daniel Ksepka, a vertebrate paleontologist who is now at the Bruce Museum in Greenwich, Connecticut. Ksepka was invited to check out the specimen, part of the collection at the Charleston Museum, when he worked at North Carolina State University in Raleigh. (The 3-decade delay in describing the species stems, in part, from the time needed to tease the delicate fossils from the rock.)
The largest bone of the bunch was an 81-centimeter-long fragment of humerus, which in humans stretches from shoulder to elbow. Ksepka’s analyses hint that the bone, if complete, would have been about 94 cm long. He extrapolated, based on the skeletal proportions of this species’ close relatives, that each wing would have measured almost 2.5 meters. Add wingtip feathers and the width of the body, and the bird’s total wingspan was likely 6.4 m but possibly larger, Ksepka reports online today in the Proceedings of the National Academy of Sciences. In comparison, the largest wild-caught specimens of today’s wandering albatross, Diomedea exulans, have a wingspan of only 3.5 m.
The new species, dubbed Pelagornis sandersi, is one of a handful within the genus Pelagornis—which means “bird of the open sea” in ancient Greek. These giant seabirds—all of them extinct and all the size of today’s albatrosses or larger—ranged worldwide, because their fossils have been found on all continents. Previously, scientists had suggested that pelagornithids, as the birds are known, were related to pelicans and albatrosses, but recent studies hint that the group is more closely related to ducks, geese, and swans.
Proportions of the weight-bearing bones in P. sandersi’s hind limbs suggest that the bird weighed between about 22 and 40 kilograms. That range, combined with the probable range of wingspans for P. sandersi, allowed Ksepka to estimate the gliding performance of the bird. For most combinations of body weight and wing proportions that he analyzed, P. sandersi outperformed a frigatebird and a vulture (two types of bird known for their soaring ability) and typically bested the gray-headed albatross, Diomedea chrysostoma. On average, Ksepka says, for every 1 meter the bird dropped while gliding, it could have moved forward 22 m.
Ksepka’s new analysis is “a solid piece of work,” says Mark Witton, a paleobiologist at the University of Portsmouth in the United Kingdom. It shows that P. sandersi “was a superalbatross,” he adds. The bird’s flight performance “is pretty much what you’d expect for a creature with that wingspan,” he notes.
Using the broad range of size and wingspan estimates to assess flight performance, rather than a single combination, “is a refreshing change from the speculations that sometimes characterize sensational finds of fossils representing truly gigantic extinct animals,” says Adam Smith, an evolutionary biologist at the North Carolina Museum of Natural Sciences in Raleigh.
P. sandersi’s body plan was well adapted to long-range flight, says Michael Habib, a vertebrate paleontologist at the University of Southern California in Los Angeles. If its winding flight paths were straightened out and then measured, “it would have been a [distance] champion,” he suggests. Habib explains that it would have been able to cross broad stretches of ocean by taking advantage of thermals (rising columns of air created over warmer-than-normal patches of ocean) to gain altitude, then gliding until it reached the next thermal.
The ability to soar long distances and forage for food with a minimum of effort might help explain how P. sandersi and its close relatives—which lived from 55 million years ago until about 3 million years ago—thrived worldwide. More mysterious, Ksepka says, is why members of this group died out. Possible causes of their demise include changes in climate that affected wind speeds over the seas, a change in the availability of preferred foods, or some combination of the two.