Giant of the Skies was a Glider

11 July 2014 by Travis Park, posted in Fossil marine birds, Pelagornithids

Pelagornithids are awesome. Back in 2012, I was fortunate enough to publish my first scientific paper. Myself, along with Erich Fitzgerald of Museum Victoria and Trevor Worthy of Flinders University reported the first occurrence in Australia on these bizarre birds known as the pelagornithids. These avians aren’t your normal seabirds, with wingspans reaching lengths of over six metres and a beak lined with menacing tooth-like projections, they would look more likely to take your arm instead of your chips at the beach (if they weren’t extinct)!

Whilst all we had to work with in our paper was the distal end of a tibiotarsus, material found elsewhere is more complete, allowing researchers to investigate the biology of these animals, including how these giants managed to stay in the air. A new paper by Dan Ksepka, Curator of Science at the Bruce Museum in Greenwich, Connecticut, published in the Proceedings of the National Academy of Sciences (PNAS), has revealed new insights into the flight performance of the pelagornithids. What’s more, he’s done it with a new species of pelagornithid that is the largest flying bird ever described.

Author of the new paper, Dan Ksepka, with the holotype of Pelagornis sandersi. Image courtesy of Dan Ksepka

Author of the new paper, Dan Ksepka, with the holotype of Pelagornis sandersi. Image courtesy of Dan Ksepka

The new newly-described species, Pelagornis sandersi, lived in what is now Charleston, South Carolina some 25–28 million years ago. Uncovered when construction workers were working on Charleston Airport, the holotype material includes a cranium,  right ramus, partial furcula, right scapula, partial right humerus, partial right radius, fragments of ulna and carpometacarpus, right femur, tibiotarsus, fibula, tarsometatarsus, and a single pedal phalanx.

Using this material Ksepka has been able to make new predictions about the aerial abilities of the pelagornithids, suggesting that they were highly efficient gliders, exploiting a long-range soaring ecology. This fits with previous ideas regarding their flight style, yet the sheer dimensions of P. sandersi exceed the limit of what some mathematical modes state is the limit for flying birds, making this first ever quantitative analysis of pelagornithid flight capabilities an important development in studying their ecology. Ksepka used Flight 1.25, a program that can predict flight performance if you plug in variables such as mass, wingspan and wing shape. The results of the analysis show that P. sandersi was able to glide at fast speeds with a relatively low amount of altitude being lost. This would have allowed the animals to maintain an expansive range to exploit feeding patches. As Ksepka notes, “That's important in the ocean, where food is patchy”.

Artist Liz Bradford's reconstruction of Pelagornis sandersi soaring above the ocean waves. Image courtesy of Dan Ksepka.

Artist Liz Bradford's reconstruction of Pelagornis sandersi soaring above the ocean waves. Image courtesy of Dan Ksepka.

Although it’s clear that P. sandersi was extremely proficient at gliding, it’s not certain whether it was capable of horizontal flapping flight, with models suggesting it was too heavy to flap for any extended length of time. The question also remains of how the animal actually got into the air; with a running takeoff or manipulating strong wind currents mooted as possibilities for launch. A lack of flapping ability would mean however that if a pelagornithid crashed into the water it would be unable to return to the air again, much like modern frigatebirds. This indirectly supports the theory that the bony projections on the beaks of pelagornithids functioned to trap prey inside once they had been plucked from the water.

Just to give you an idea of how big this bird actually was, here is a illustration comparing it to a condor and an albatross, the largest living volant birds. Illustration by Liz Bradford, courtesy of Dan Ksepka.

Just to give you an idea of how big this bird actually was, here is a illustration comparing it to a condor and an albatross, the largest living volant birds. Illustration by Liz Bradford, courtesy of Dan Ksepka.

The dimensions of this bird are incredible. The skull is nearly 60 cm long, the humerus is estimated to be an astounding 94 cm, with the estimated total wingspan is between 6.06 and 7.38 m once the feathers are taken into consideration! These birds were truly impressive and it is a real shame that they went extinct (which is yet another unanswered question about this mysterious group). It doesn’t take a genius to see why I have a real soft spot for the subject of my first publication and why I sincerely hope to work on them again one day. Fantastic work by Dan on the paper, I look forward to hearing more about these fascinating, bizarre creatures.

References

Daniel T. Ksepka (2014) Flight performance of the largest volant bird. Proceedings of the National Academy of Sciences (advance online publication) doi: 10.1073/pnas.1320297111

Fitzgerald, E. M. G., Park, T., and T. Worthy. 2012. First giant bony-toothed bird (Pelagornithidae) from Australia. Journal of Vertebrate Palaeontology 32:971–974


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