The Oldest Airborne Vertebrate Animal Was a Reptile With ‘Weird’ Wings

Paleontologists describe a 255-million-year-old weigeltisaurid fossil that likely glided through the air with the help of expansive winglike membranes

Fossilized weigeltisaurid skeleton on beige background
Scientists pulled this weigeltisaurid fossil out of an outcropping of copper shale in Germany in 1992. Now, Smithsonian paleontologists have fully described this animal, the oldest known vertebrate capable of gliding through air. Pritchard et al. 2021

Since the Middle Ages, humans have mined a rich deposit of shale stretching across Europe for copper, zinc, silver — and fossils. In 1992, a fossil collector in eastern Germany pulled a strange skeleton out of the mining refuse from this rocky layer. It had a pointy crown of horns, thin limbs and peculiar rods stretching out from its chest.

“These are a really weird set of bones. They don’t seem to exist in pretty much any other vertebrate animal,” said Adam Pritchard, an assistant curator of paleontology at the Virginia Museum of Natural History and former Peter Buck postdoctoral fellow at the Smithsonian’s National Museum of Natural History.

The fossil, it turns out, is an ancient reptile named Weigeltisaurus jaekeli, a reptile that lived over 250 million years ago — before the dinosaurs. Pritchard and Hans-Dieter Sues, curator of vertebrate paleontology at the museum, have published a new detailed analysis of the specimen in the scientific journal PeerJ. They posit that the animal, known as a weigeltisaurid, used those bony rods to support winglike membranes used for gliding, making it the oldest-known airborne vertebrate animal.

Weigeltisaurus jaekeli likely used its wide, winglike membranes to glide from branch to branch in the late-Permian forest. Paleontologists reconstructed the reptile’s anatomy in this drawing to illustrate its skeleton’s proportions. Pritchard et al. 2021

A strange specimen

The fossil hunter found the strange skeleton by splitting pieces of shale, cracking the fossil into two slabs. One slab ended up in the hands of a private collector and likely contains pieces of the reptile's bones. The other slab held most of the skeleton and landed in the collection of the State Museum of Natural History in Karlsruhe, Germany. Scientists pinpointed the fossil in the second slab as a Weigeltisaurus, which was first described from another fossil in 1930, but the reptile's body shape still remained an enigma to paleontologists.  

Over the years, some researchers suggested that the long bones protruding from the specimen’s abdomen could have allowed the animal to glide through the air like a flying squirrel. But the skeleton in the fossil is curved in on itself and some bones are overlapping, making it hard to tell if they’re just ribs, or something else.

Researchers cleaned the Karlsruhe fossil to expose its bones more clearly before analysis. The positioning makes it difficult to deduce the function of the long horizontal bones pictured at the fossil’s center. Diane Scott

“There are very few things like it,” Sues said of the fossil. A few other specimens from the same species have also been unearthed in England, Russia and Madagascar, but the fossil housed in the Karlsruhe Museum provides the most complete example of the animal’s anatomy. “This is definitely the one that brings it all together,” Pritchard said.

Pritchard saw the skeleton referenced in the scientific literature over the years as a grad student researching the evolution of early reptiles during the Permian Period, which lasted between 299 and 251 million years ago. “But no one had really gone in and done a very fine, detailed analysis of the skeleton of these animals.” When Pritchard came to the Smithsonian as a postdoc in search of a meaty project to dig his teeth into, Sues suggested he take a closer look at the weigeltisaurid.

Quality fossil time

Pritchard flew to Germany for a week to pore over the fossil at its home in the Karlsruhe museum’s collections. “I'm of the mind that if you're going to make a fossil the focus of a study you should spend a very large amount of quality time with it in person,” he said.

He took pages of copious notes, making an inventory of all the individual bones and building his own interpretation of how they all might fit together. “And then I photographed the heck out of it,” Pritchard said, to be sure he wouldn’t miss one tiny detail in the bones once he came back to the Smithsonian.

The weigeltisaurid specimen used in the bulk of Pritchard and Sues’ study is housed in the State Museum of Natural History in Karlsruhe, Germany. Adam Pritchard

After painstakingly measuring every rib, finger and toe, Pritchard laid out the weigeltisaurid’s

bones in several drawings and diagrams. He also mapped where the animal might fit on the reptile family tree by comparing each of its anatomical traits with those of other ancient lizards. Though it probably looked something like a chameleon, the weigeltisaurid belongs to an evolutionary line that split off from the lizards, crocodiles and snakes we know today.

“These are a more ancient lineage than any of those animals,” Pritchard explained.

Unique gliders

Initially, Pritchard looked at this project as a chance to explore a curious fossil on a deep level. “But as I got into the work, it became clear to me that there was one question that kind of remained. And that is the identity of the bones that seem to have formed the gliding membrane,” he said.

Pritchard and his colleagues’ analysis shows that there are more wing bones than vertebrae and that they lay separate from the rest of the skeleton, confirming that they would have supported two wide flaps extending from each side of the animal’s abdomen. This is a singular trait, Sues explained. There are gliding lizards that exist today, but their “wings” are attached to their ribs, he said.

While Pritchard and Sues are confident that weigeltisaurids were gliders, there’s not a lot else known about the animal’s life history. “I would love to know how they grew,” Pritchard said. “What did it look like when it popped out of the egg?” He also wonders about what the weigeltisaurid snacked on. His best guess is bugs, but he can’t be totally sure unless some direct fossil evidence turns up. “We don’t have a weigeltisaurid with insect material inside its abdominal region. But that would be cool,” Pritchard said.

Though he’s not currently working on these questions, Pritchard said that learning more about weigeltisauird and its relatives can give us a better appreciation for the diversity of reptiles — even before dinosaurs came on the scene. “Among paleontologists there’s this sense that once you get into the age of dinosaurs, that’s when reptiles really take off, develop all kinds of amazing features and just come into their own,” he said. But earlier animals like Weigeltisaurus are proof that reptiles have always been “super weird,” he explained. “They’re doing strange things that, if we didn’t have the fossils, we never would have expected.”

Editor's note: the headline was updated to clarify that the repitle was the oldest airborne vertebrate animal. 

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