How did the world’s largest pterosaur fly?

Palaeontologists have painted the most complete picture yet of the world’s largest pterosaur, in six new papers published in a collection by the Journal of Vertebrate Paleontology.

Living 70 million years ago in inland marshes and open fields, Quetzalcoatlus was the biggest pterosaur and the biggest animal to ever take to the skies. Individuals stood at 3.6 metres tall and had a 12-metre wingspan – at least 50% bigger than the wings of the largest known bird.

But since palaeontologists only have a few fossilised bones, they know very little about Quetzalcoatlus. They previously didn’t know what it ate, how it walked with such massive wings, or how it launched itself into the air to fly.

Now, this new analysis reveals that Quetzalcoatlus likely leapt at least 2.5 metres into the air, before sweeping its wings to lift off.

“This ancient flying reptile is legendary, although most of the public conception of the animal is artistic, not scientific,” says Kevin Padian from the University of California, Berkeley, co-author on one of the papers.

“This is the first real look at the entirety of the largest animal ever to fly, as far as we know. The results are revolutionary for the study of pterosaurs — the first animals, after insects, ever to evolve powered flight.”

The six new papers help palaeontologists flesh out the bones of these giant airborne creatures. They not only describe how the species moved both on the ground and in the air, but also the pterosaur’s geological and ecological environment, its anatomy and its taxonomy.

Illustration of pterosaur skeleton
A sketch of the bones of Quetzalcoatlus northropi. When walking, the animal had a unique gait unlike any other, and distinctly different from that of the vampire bat. Credit: John Conway

The studies looked at the fossilised wing bones of the huge Quetzalcoatlus northropi, found in the late 1970s from Big Bend National Park in Texas, and compared them with dozens of specimens of a smaller Quetzalcoatlus species, about half the size of Q. northropi. The more complete skeletons of the smaller species allowed the team to apply findings to their larger cousin.

The research team found that Quetzalcoatlus was somewhat similar to today’s egrets and herons in how it fed, wading and stalking through rivers and streams.

“The jaws are very long and thin, tapering to a point,” Padian says. “And if you look at a heron or egret’s jaws, they’re the same — good for plucking lizards and other small game, but definitely not carcass-scavenging. It had no teeth.”

Instead, its long toothless jaw was likely used to sift crabs, worms and clams from the mud at the bottoms of lakes and rivers.

The larger species may have hunted alone, while the smaller species could have flocked together in lakes; at least 30 individuals were found at one fossil site.

The pterosaur was also similar to herons and egrets in how it launched itself into flight – using strong rear legs to jump to twice its hip height, then beginning to flap its wings as soon as it had enough ground clearance.

But the pterosaur was more similar to condors and vultures in how it actually soared through the air.

“Pterosaurs have huge breastbones, which is where the flight muscles attach, so there is no doubt that they were terrific flyers,” Padian says. “Their upper arm bone — the humerus — has huge, bony crests for anchoring the flight muscles, which are larger than those of birds and far larger than those of bats.

“The wings worked essentially like those of birds and other dinosaurs, to which pterosaurs are most closely related.”

Based on how the pterosaur could move its head, neck and jaw, the researchers also think it may have been able to spot prey from the air and swoop down to catch it.

The studies also examined how the pterosaur was able to walk with such huge wings. It walked on two legs, but even when folded up, its wings still touched the ground. So how did it avoid tripping?

“The animal first raised its left arm, then advanced its left leg in a full step, then it placed the hand on the ground,” Padian explains.

“The process was repeated with the right limb: the right arm lifted, the right leg advanced and emplaced the right foot, and then the right hand descended. It seems a cumbersome process to us, but the animal could execute the gait quickly and easily.”

Darren Naish, a pterosaur expert who was not involved with the research, says that this set of papers is a milestone for understanding this species. “To say that this work is long awaited is something of an understatement,” he says. “Never before has so much detailed information on azhdarchids (the pterosaur family that includes Quetzalcoatlus) been gathered in the same place. This work will serve as the standard go-to study of this group for years – probably decades – to come.”

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