Birds With 6.10 m Wingspans Once Patrolled the Skies of Antarctica

Birds With 6.10 m Wingspans Once Patrolled the Skies of Antarctica
An artist's depiction of a pelagornithid, with its prominent toothed beak, being harassed by ancient albatrosses. (Illustration: Brian Choo)

A re-analysis of two fossils found in the 1980s has led to the discovery of an absolutely enormous Antarctic seabird.

The modern wandering albatross, with its 3.5-metre wingspan, is damned impressive. But this newly described bird, with wings stretching nearly 6 metres, is the stuff of imagination. Living during the Eocene between 50 million and 40 million years ago, this oversized pelagornithid, or “bony-toothed” bird, prowled the Antarctic skies in search of squid and fish, according to research published today in Scientific Reports.

The newly described bird was identified from two fossils: a foot bone and the middle portion of a lower jaw. The fossils were originally uncovered by a research team from the University of California Riverside, who found the pieces on Antarctica’s Seymour Island during two different expeditions. The specimens eventually made their way to the UC Museum of Paleontology at UC Berkeley and were promptly forgotten.

Five years ago, Peter Kloess, a co-author of the new study and a paleontologist at UC Berkeley, was browsing through the museum collection in hopes of finding something interesting, which he did.

“I love going to collections and just finding treasures there,” Kloess, who was still a grad student at the time, said in a UC Berkeley release. “Somebody has called me a museum rat, and I take that as a badge of honour. I love scurrying around, finding things that people overlook.”

Figuring he found something quite overlooked, Kloess, along with Ashley Poust from the San Diego Natural History Museum and Thomas Stidham from the Chinese Academy of Sciences in Beijing, decided to take a closer look at the two fossils. As the authors sum up in their new paper, “these Antarctic fossils demonstrate the early evolution of giant body size in [pelagornithids], and they likely represent not only the largest flying birds of the Eocene but also some of the largest [flying] birds that ever lived,” featuring wingspans between 5 and 6 metres.

Indeed, these birds are comparable to other extinct giants, namely Pelagornis sandersi (another pelagornithid), with its 6 to 7.3 metre wingspan, and Argentavis magnificens, which had a wingspan measuring 7 metres.

Of course, we’re talking about birds capable of flight; flightless, extinct elephant birds weighed upwards of 500 kg. And I’d be remiss to ignore the pterosaurs (not birds), with their jaw-dropping 10 metre-long wingspans. The species described in the new study is important in that it appeared far earlier in evolutionary history than these other avian giants (P. sandersi, for example, appeared between 25 million and 28 million years ago).

Pelagornithids were a successful group of bony-toothed birds that went extinct 2.5 million years ago following a 60-million-year reign. The giant pelagornithid described in the new study dates back to at least 50 million years ago, which is significant from an evolutionary perspective.

The new fossil discovery “shows that birds evolved to a truly gigantic size relatively quickly after the extinction of the dinosaurs and ruled over the oceans for millions of years,” explained Kloess. For context, the Cretaceous–Paleogene extinction event that wiped out all non-avian dinos happened 66 million years ago.

The five-inch segment of fossilized jaw. (Image: Peter Kloess/UC Berkeley ) The 12.7cm segment of fossilised jaw. (Image: Peter Kloess/UC Berkeley )

Pelagornithids are known as bony-toothed birds on account of the projections, or struts, on their jaws. These aren’t really teeth, as they’re covered in keratin, which is what our fingernails are made of. Scientists refer to these protrusions as “pseudoteeth,” but there’s nothing pseudo about them in terms of function, as these sharp bits were used to snag squid and fish from the oceans.

The lower jaw portion, approximately 40 million years old, still exhibits some pseudoteeth, but they’re badly worn down from erosion. Kloess and colleagues figure they were around 3 cm when the bird was alive. This jaw was once affixed to a rather large bird skull measuring 60 cm long. Careful measurements of the struts in terms of spacing and size, along with a comparative analysis of other known pelagornithids, pointed to the bird’s large size, making it one of the largest known members of this bony-toothed group. The spacing of the teeth also helped to distinguish the specimen from other pelagornithid species.

By reviewing notes left by the original researchers, the team realised that the fossil foot bone — a tarsometatarsus (a long bone of the lower leg) — was pulled from an older geological formation than presumed. This means the fossil is 50 million years old, as opposed to the originally presumed 40 million years old.

Back then, Antarctica had a warmer climate, and the surrounding oceans were filled with early penguins and extinct relatives of ducks, ostriches, and petrels, among other bird groups. The gigantic predatory pelagornithids remained an important member of this ecosystem for over 10 million years, the new research suggests.

“In a lifestyle likely similar to living albatrosses, the giant extinct pelagornithids, with their very long-pointed wings, would have flown widely over the ancient open seas, which had yet to be dominated by whales and seals, in search of squid, fish and other seafood to catch with their beaks lined with sharp pseudoteeth,” explained Stidham in the UC Berkeley release. “The big ones are nearly twice the size of albatrosses, and these bony-toothed birds would have been formidable predators that evolved to be at the top of their ecosystem.”

More fossil evidence would help to bolster the estimates provided in the new study. Still, the new paper offers some fascinating insights into life during the Eocene, with the dinosaur extinction event firmly in the rear view mirror.