New 'frozen dragon' pterosaur found hiding in plain sight

The flying reptile was mostly head and neck—and had at least a 16-foot wingspan, if not bigger.Wednesday, 11 September 2019

A new study in the Journal of Vertebrate Paleontology describes a new pterosaur called Cryodrakon boreas, ‘frozen dragon of the north winds.‘ The flying reptile had a wingspan of at least 16 feet and may have grown to a wingspan of up to 33 feet, the size of its relative Quetzalcoatlus northropi.
A new study in the Journal of Vertebrate Paleontology describes a new pterosaur called Cryodrakon boreas, ‘frozen dragon of the north winds.‘ The flying reptile had a wingspan of at least 16 feet and may have grown to a wingspan of up to 33 feet, the size of its relative Quetzalcoatlus northropi.
photo by Illustration by David Maas

In the icy badlands of Alberta, palaeontologists have found a “frozen dragon”: a new genus of pterosaur that once soared over the heads of dinosaurs with a wingspan that stretched at least 16 feet. The flying reptile—named Cryodrakon boreas—lived in what is now western Canada about 76 million years ago, during what’s known as the Cretaceous period.

“The animal, when alive, would not have been a frozen dragon,” notes study coauthor Mike Habib, a palaeontologist at the University of Southern California. “It would have flying in a landscape that would have been reasonably temperate ... but a hell of a lot warmer than central Alberta is now.”

The pterosaur’s bones have been known to scientists for nearly three decades, but it has only now been confirmed as its own genus, researchers announced on Tuesday in the Journal of Vertebrate Paleontology.

“For me, as a Canadian who also works on pterosaurs, it’s pretty cool to get an actual name for an animal that’s been kicking around for a while,” says palaeontologist Liz Martin-Silverstone, a research associate at the University of Bristol who wasn’t involved with the study.

For a long time, palaeontologists had instead assumed that the fossils belonged to a pterosaur called Quetzalcoatlus northropi, says study coauthor Dave Hone, a paleontologist at Queen Mary University of London. Both animals belong to a group known as the azhdarchid (azh-DAHR-kid) pterosaurs, which were notable for being mostly head and neck.

The azhdarchids are also known for reaching immense sizes, none more so than Quetzalcoatlus. When flying over what’s now Texas, the creature’s wingspan stretched more than 30 feet. When it was walking on the ground, as azhdarchids often did, it was more than eight feet tall at the shoulder, roughly the same height as some giraffes.

The discovery of Cryodrakon means North America was home to at least two genera of large azhdarchids, expanding our knowledge of ancient diversity and how the world’s largest flying creatures eked out a living.

Tricky pterosaurs

The partial skeleton that defines Cryodrakon was dug up from Canada’s Dinosaur Provincial Park in 1992. But its identity remained unclear for decades because of a paleontological paradox: Quetzalcoatlus might be the best-known and worst-known azhdarchid all at once.

Though Q. northropi was described in 1975, only one of its limb bones got a detailed writeup; the scientists who oversaw the giant’s remains never got around to publishing the rest. For 40 years, paleontologist Wann Langston worked off-and-on to complete the description—but then he died in 2013, leaving the work unfinished. An international team is currently trying to finish the job.

In the meantime, North American palaeontologists have been caught in a catch-22. If they found pieces of what looked like a large Cretaceous azhdarchid, they provisionally assigned them to Quetzalcoatlus, because they didn’t know enough about Quetzalcoatlus to say anything different.

“You’ve got this weird situation where Quetzalcoatlus is basically the first azhdarchid to be named, so it becomes the definition of the [group], and yet there’s no good description of it,” says Hone, who describes the situation as “a giant loop of not being able to solve the problem properly.”

Two key advances offered a way off the Quetzalcoatlus merry-go-round. In the past 15 years, paleontologists have found more types of azhdarchids in France, Morocco, Kazakhstan, Hungary, Romania, and elsewhere, giving a much better reference for diversity within this pterosaur group. In addition, a small number of researchers have since gotten the chance to see the Quetzalcoatlus fossils up close—including Habib, who measured the bones to model how the creature flew.

As a point of comparison, Habib visited Canada’s Royal Tyrrell Museum to see the partial pterosaur skeleton dug up in 1992, whose limb bone is among the best preserved in the world.

The remains first gained notoriety for their scars. The bones bear scratches and an embedded tooth that appear to be from a scavenger, most likely a relative of Velociraptor. But Habib soon saw more intriguing features. The more that he compared his measurements of Quetzalcoatlus to the Canadian fossil, the more he suspected it wasn’t Quetzalcoatlus at all.

Game of bones

Because the Canadian remains make up a partial skeleton, Habib’s colleague Hone had enough material to place the pterosaur on the azhdarchid family tree. He then zoomed in on the neck vertebra, whose ends are shot through with pneumatophores, the holes through which air sacs once entered the bone’s interior.

The arrangement of these pneumatophores can help scientists tell pterosaur species apart. And when Habib, Hone, and Royal Tyrrell Museum paleontologist François Therrien compared the holes in the Canadian pterosaur’s neck vertebrae against those for all other known azhdarchids, they found that its arrangement is unique.

To recognise the modern climate in the region where this pterosaur once roamed, they named the new pterosaur Cryodrakon boreas, or “the cold dragon of the north winds.” Habib, a fan of the TV show Game of Thrones, had also suggested Cryodrakon viserion, a reference to one of the show’s dragons, in part because of its rise from the ice, and in part because the animal might have reached movie-monster proportions.

The main reference fossil for Cryodrakon belonged to an individual pterosaur that had a roughly 16-foot wingspan. But the researchers realised that a separate fossil at the Royal Tyrrell Museum—a smashed-up tube of bone 16 inches long—was the middle portion of a neck vertebra from an azhdarchid that probably had a wingspan of more than 30 feet.

With its ends broken off, that vertebra had avoided identification for years: Paleontologists had even once tentatively described it as a leg bone. Because the fossil is fragmentary, researchers can’t say for sure whether it belongs to Cryodrakon, but the neck vertebra is definitely from an azhdarchid, and Cryodrakon is now the only known azhdarchid from that place and time.

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“There is a 9- to 10-meter wingspan azhdarchid in this formation; whether or not that’s exactly the same as the one we’ve described, you can’t say 100-percent,” Hone says. “It’s like you go out to Africa, and you find some giant cat tooth—it’s probably a really big lion, but without the rest of the lion attached to it, it’s a tooth!”

Martin-Silverstone agrees with the cautious approach: “I think they’re right that it’s an azhdarchid [neck] vertebra—I’ve seen this specimen, and I completely agree that that’s what it is,” she says. “But I would be much more conservative in saying it’s Cryodrakon, because, yeah, there’s no features on that at all.”

More work on Cryodrakon may help crack the mystery and add more clues to this large pterosaur’s lifestyle. Habib, for one, still wants to use the limb measurements to calculate how it flew—the project that inadvertently turned up the frozen dragon in the first place.

Future analysis could even peer deeper inside the pterosaur’s bones. Taissa Rodrigues, a paleontologist at Brazil’s Federal University of Espírito Santo who wasn’t involved with the study, says that taking thin sections of Cryodrakon bones could reveal how the pterosaur grew from hatchling to adult. Future fossils, she adds, could even test whether Cryodrakon varied in size based on sex.

“It’s amazing,” she says, “just to see how far we’re going.”

Fossils 101
Fossils 101
Fossils are echoes of an ancient past. Find out about the two major categories of fossils, how fossilisation occurs, and how fossils can help paint a picture of the planet's history.
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