In 1983, construction workers who were building a new terminal at the Charleston Airport in South Carolina made an unusual discovery—pieces of a large fossilized skeleton, including parts of a skull and limb bones. Paleontologists from the nearby Charleston Museum were called in to investigate the find, and museum director Albert Sanders dispatched a team headed by staff member James Malcolm to excavate the skeleton.
"Museum Pieces" is a diary series that explores the history behind some of the most interesting museum exhibits and historical places.
The geological deposits here were around 25 million years old, from the Miocene era. At this time, the Earth’s global temperature was quite a bit warmer than today, and the sea level was considerably higher. Most of South Carolina was at the bottom of a shallow tropical sea. These layers of rock had already yielded fossils of ancient marine life, including extinct sharks and primitive whales.
But the bones from the airport were different: although large, they were very thin-walled, and their interior was hollow and filled with what had once been air sacs to lighten them. These were adaptations typical of birds, which reduced the weight of the bones to make flight easier, and Sanders recognized them as the skeleton from an odd group of ancient birds called pelagornithids.
The birds first evolved during the Jurassic period, from a group of dinosaurs closely related to the famous Velociraptor. At the end of the Cretaceous 65 million years ago, when a mass extinction wiped out the dinosaurs and other groups such as the flying pterodactyls and the marine mosasaurs, the birds continued, and soon evolved to fit into many of the ecological niches that had been left empty by the disappearance of the extinct Cretaceous animals—known as “adaptive radiation”.
By about 50 million years ago, a particular group of ancient birds had adapted to fill one of the ecological niches that had been occupied by the now-extinct pterodactyls. The first pelagornithid to be discovered was found in France in 1869. Consisting of a single wing bone recovered in shallow marine deposits, it was given the scientific name Pelagornis miocaenus, which means simply “Miocene ocean bird”. Almost nothing was known about it. Over the decades, however, new specimens were found in California, Oregon, Maryland, South Carolina, Peru, Chile, Portugal, Morocco, and New Zealand. All of them were found in marine deposits: the pelagornithids were apparently a wide-ranging group of ocean-going birds that must have been fairly common in Miocene seas.
Bird skeletons are, by nature, however, very delicate, and the thin-walled bones did not preserve very well. As a result, most of the fossil finds consisted only of single bones or portions of a limb or skull, and most of these were broken and smashed. As a result, it was very difficult to compare specimens, and paleontologists tended to assign each individual find to its own genus or species. On rare occasions, new finds allowed these names to be consolidated: in one instance a new partial skeleton allowed three other bones, a skull from Dasornis, a leg bone from Neptuniavis, and a wing bone from Argilliornis—which had each been given their own names—to be recognized as different parts of the same bird.
The scrappy and incomplete nature of the finds also made it difficult to determine the evolutionary relationships of the pelagornithids. Authorities who studied the same bones came to radically different conclusions: some decided that the pelagornithids were primitive relatives of the pelicans and storks, while others argued that they were ancient cousins of the ducks and geese.
Despite the taxonomic mishmash, the pelagornithids shared some common characteristics. One unusual trait was their size. They were extraordinarily large birds—even the smallest of them were larger than the modern albatross. At this time, the largest known flying bird was Argentavis magnificens, a 6 million year old relative of the vultures with a wingspan of up to 7 meters (about 23 feet). The largest of the pelagornithids rivaled this, exceeding 6 meters.
But the oddest and most significant trait of the pelagornithids was found in their beaks. The earliest small birds of the Jurassic, such as Archaeopteryx, had the same type of socketed teeth as their raptor dinosaur ancestors, which probably helped them to seize and hold insect prey. But as birds evolved to become bigger and better fliers, they lost their teeth as an adaptation to reduce their weight, replacing their socketed teeth with a lightweight but strong beak made of a hornlike sheath that grew from the jawbones.
The pelagornithids appear to have led a life somewhat like a modern albatross or some of the ancient pterodactyls, soaring long distances over open oceans and catching fish near the surface for food. (Fossil skulls show signs of a salt gland near the eyes, allowing them to drink sea water and excrete the excess salt). Holding on to a slippery wriggling fish while flying is difficult, however, and although the pelagornithids, like all birds, had lost their teeth long ago, they now evolved a replacement called “pseudoteeth” to help them grip their prey. These consisted of ragged sawlike points that projected from the edge of the jawbone into the mouth, and were covered in life by the same hornlike proteins that made up the bird’s beak. Although they looked and functioned like teeth, they had no sockets and no enamel, and they were not grown and replaced like real teeth—if one of these sharp projections happened to break off, it was permanently lost.
It was an elegant evolutionary solution, and it became the defining characteristic of the pelagornithids, who were also known to scientists as the pseudodontorns, or “false tooth birds”. The pelagornithids became a quite successful group, found as fossils in ocean deposits across the world from about 50 million years ago to about 2 million years ago.
At the Charleston Airport, Sanders saw that the new skeleton he had recovered consisted of a shoulder blade, some wing bones, some leg bones, and most of the skull. The nearly-complete jaws bore the ragged “pseudoteeth” typical of the pelagornithids, and Sanders therefore tentatively identified it as a species in the genus Pelagornis, bits and pieces of which had already been found at other locations in South Carolina. Using a backhoe to pull out the entire stone block containing the fossils, he painstakingly transported it to the Charleston Museum, where it was first placed into storage and then underwent the long process of “preparation” to remove the delicate bones from the rock. It wasn’t until 2013 that the cleaned fossils were ready for study, and bird expert Daniel Ksepka was able to take a detailed look.
Immediately, Ksepka recognized that the bones were noticeably larger than any other specimen of pelagornithid, and he named it as a new species, Pelagornis sandersi (in honor of the museum director who had excavated it). Extrapolating from measurements he was able to take, he estimated that the bird stood about as tall as a human and had a total wingspan somewhere between 6.1 meters and 7.4 meters (between 20 and 24 feet). This made P. sandersi likely larger than the teratorn Argentavis, the previous record-holder, making Pelagornis the largest-known flying bird—over twice the size of today’s largest albatross. (Pelagornis was not, however, the largest flying creature—the pterodactyl Quetzalcoatlus was as tall as a giraffe and had a wingspan of 11 meters, or some 33 feet.)
Using computer modeling, Ksepka estimated the giant bird’s weight at somewhere between 50 and 90 pounds. Even with a conservative estimate, this exceeded the aerodynamic limit for bird wings: at a weight of more than 5 pounds per square foot of wing area, a bird would not be able to produce enough lift by flapping to get itself off the ground. The joints in the wing bones in this skeleton were also not well-suited for flapping motions, but were apparently capable of locking the extended wing into place as a fixed aerodynamic plane. Ksepka therefore concluded that, once Pelagornis got itself off the ground (by running downhill into the wind or launching itself from a cliff face, like a hang glider) it flew in a manner similar to the modern albatross, gliding on wind and thermal air currents to provide lift and rarely flapping its wings. Using very little energy, albatrosses can glide over the ocean for days at a time, and it seems likely that Pelagornis lived a similar lifestyle. Since the legs on the skeleton are short and relatively weak, the giant birds apparently did not spend much of their time on the ground.
The original fossil bones of Pelagornis are kept in a secure storage area at the Charleston Museum. A reconstruction of a complete skeleton is now the centerpiece of a new “natural history” wing of the museum, which displays various fossils found in South Carolina. An exhibit tells the story of the discovery of Pelagornis.
NOTE: As some of you already know, all of my diaries here are draft chapters for a number of books I am working on. So I welcome any corrections you may have, whether it's typos or places that are unclear or factual errors. I think of y'all as my pre-publication editors and proofreaders. ;)