In 1983, excavations for a new terminal at the Charleston International Airport in Charleston, South Carolina, began with a bang, as metal hit bone. The construction workers had stumbled upon a fossil so big that it required a backhoe to unearth. Now, over thirty years later, the remains have been identified as that of the largest known bird ever to have flown our skies.
The creature lived 25 to 28 million years ago and had a wingspan of 20 to 24 feet—twice that of the largest volant (i.e., flying) bird alive today, the wandering albatross. Like the albatross, this ancient enormous bird soared long-range over the ocean, but how it managed to do so with a mass and wingspan that seemingly defies aerodynamic theory had, until recently, been a mystery.
"Anyone with a beating heart would have been struck with awe," paleontologist Daniel Ksepka told Reuters. Kspeka's study of the bird’s flight performance was published Monday in the Proceedings of the National Academy of Sciences. "This bird would have just blotted out the sun as it swooped overhead. Up close, it may have called to mind a dragon."
Kspeka has identified the fossil as belonging to a hitherto unknown species of pelagornithid, a group of giant seabirds birds that appeared in the Paleocene (66 to 56 million years ago, i.e. post-dinosaur extinction) and attained a global distribution before going extinct in the Pliocene Epoch (5.3 million to 2.6 million years ago). The pelagornithid remains found on every continent have in common large size, highly modified wing bones, and beaks lined with bony tooth-like spikes. Kspeka’s study, “Flight performance of the largest volant bird” uses data from the fossil of the latest and greatest pelagornithid species—named Pelagornis sandersi in honor of the former Charleston Museum curator Albert Sanders, who collected the fossil—to explain the bird's ability to soar.
“Pelagornis sandersi surpassed theoretical mass limits for flapping flight and wingspan limits for soaring flight based on previous models," says Kspeka, "but the extremely elongated wings and reduced hind limbs indicate it was a volant bird.” Using computer modeling, Kspeka was able to calculate aerodynamically viable flight parameters for the Pelagornis sandersi.
Kspeka’s findings indicate that the species was capable of highly efficient gliding flight. The bird likely launched from a running takeoff and obtained and renewed power from air currents. Its long wings would have reduced the relative size of wingtip vortices, Ksepka writes in the study, “reducing drag and thereby, improving glide ratio.” His modeled flight properties “indicate that P. sandersi attained high light:drag ratios in gliding flight and was able to glide at fast speeds with low sink rates.” Thus the bird would have been capable of capturing prey near the ocean’s surface while remaining in flight. This theory is “in keeping with the proposed gripping or trapping function of the psuedoteeth” common to all pelagormithids.
But the cause of these bird's extinction remains as mysterious as their ability to fly once was. “Our understanding of the ecology of pelagornithids is only starting to develop,” Ksepka writes. “New data suggest that they were remarkably efficient flyers, which together with their global distribution across all seven continents and long temporal range, makes the cause of their ultimate extinction all the more mysterious.” Thus mysteries of the remains...remain.