Feathers were common among dinosaurs, but scientists aren’t certain if the fur-like coverings of pterosaurs—a group of flying reptiles—were of the same sort seen on dinos and birds or something completely different. The discovery of two exquisite fossils in China now suggests pterosaurs were very much covered in feathers, potentially pushing back the origin of this critically important evolutionary feature by 70 million years.
Pterosaurs lived between 230 million and 66 million years ago, and they were the first vertebrates to achieve true flapping flight. These ancient creatures lived alongside dinosaurs, and though they’re frequently represented in the media and in film, scientists actually know very little about them. Fossil evidence suggests they were covered in pycnofibres—a fuzzy, fur-like coating—but palaeontologists are divided on whether or not these coatings were similar to the feathered skin coverings seen on dinosaurs and birds, or if pterosaur pycnofibres represented something different entirely.
New research carried out by palaeontologists from the University of Bristol, Nanjing University, University College Cork, and several other institutions, now shows that pterosaurs featured not one but four different types of feathers. The new study, published today in Nature Ecology & Evolution, suggests pycnofibres are true feathers, pushing back the origin of feathers by about 70 million years.
The four feather types described in the new study: filaments, filament bunches, tufted filament, down feather. Image: Zixiao Yang
To be clear, these feathers aren’t like the ones we see on today’s birds. In the case of pterosaurs, three of the four feather types were filament based, appearing as either hair-like structures, bundles, or tufts. The fourth kind was the more familiar down feather. The authors of the new study, led by Michael Benton from the University of Bristol, said the primary purpose of these feathers was to provide insulation, but they could have also been used for tactile sensing, camouflage, and aerodynamics (but not flight).
These findings are based on two fossil specimens found at a site in Inner Mongolia—a site that also yielded evidence of ancient lakes, fish, insects, salamanders, and dinosaurs. The two pterosaurs, which date back to around 160 million to 165 million years ago, were chosen for the study because they were exceptionally well preserved and “absolutely covered in fur,” in the words of Benton. What’s more, the fossils were uncoated, meaning scientists hadn’t covered them in a protective coating like a lacquer. “We need a clean surface for our studies,” Benton told Gizmodo. The two species are Anurognathids, a family of pterosaurs. Both are small, likely juveniles, with wingspans no longer than 35 inches (90 centimetres). The two specimens are likely either Jeholopterus ningchengensis or Dendrorhynchoides curvidentatus.
The researchers used four different techniques to study the fossils, including conventional microscopes, scanning electron microscopes, fluorescence microscopy, and laser-stimulated fluorescence imaging. Together, these techniques allowed the researchers to study the fine structures at microscopic scales and to peer inside the fossils themselves. Remarkably, the researchers were able to observe melanosomes—a cellular organelle that synthesises melanin pigment—inside the feathers, suggesting these creatures had a ginger-brown colouring.
Laser-Stimulated Fluorescence (LSF) image of the pterosaur specimen. Image: Michael Pittman and Thomas G. Kaye
Scientists had previously suggested the existence of only one simple type of pycnofibre, but the new analysis suggests the presence of at least four. The researchers reached this conclusion after focusing on areas within the fossil where the feathers didn’t overlap, and where the feather structures were clearly visible. No anatomical evidence suggesting these structures were somehow different from those of birds of dinosaurs were detected, leading the researchers to conclude a single evolutionary origin of feathers, about 250 million years ago, long before the appearance of birds.
These purported pterosaur feathers date back to the Middle Jurassic, about 160 million to 170 million years ago. Some of the oldest-known feathers in the fossil record date back to the same period, but the difference here is that the occurrence of these feathers, and the animals they adorned, were plotted on the evolutionary tree (i.e. a phylogenetic analysis). This analysis projected the origin of feathers back to the common ancestor of pterosaurs and dinosaurs, namely ornithischians (plant-eating dinosaurs) and theropods (two-legged carnivorous dinosaurs and the ancestors of all birds)—a branching that occurred during the early Triassic, around 250 million years ago.
“We now know that feathers originated long before birds, and for insulation. What we didn’t know is that they were likely a shared structure across all dinosaurs as well as pterosaurs,” said Benton. “This brings their origin deeper in time to the Early Triassic when life was recovering from the devastation of the end-Permian mass extinction.”
Palaeontologist Armita Manafzadeh from Brown University, who wasn’t affiliated with the new study, said the researchers’ approach to studying these fossils was “remarkably integrative,” and a “gold standard” for this kind of analysis.
“They used four complementary methods to analyse not only the shape but also the cellular and chemical composition of pycnofibers, giving us a much more thorough understanding of pterosaur integumentary [skin] structures than ever before,” Manafzadeh told Gizmodo. “This work goes to show us that synthesising different methods can help us extract previously inaccessible data from fossils—and also that we still have a lot left to learn about pterosaurs,” she said.
Steve Brusatte, a palaeontologist at the University of Bristol who wasn’t involved in the new study, said these two new fossils are “incredibly” important.
“I think they show once and for all that pterosaurs had feathers, just like birds, and just like many dinosaurs,” Brusatte told Gizmodo. “If you just looked at the fluffy structures on these pterosaurs, and knew nothing about the skeleton they were attached to, you would think they were from a raptor dinosaur. If pterosaurs had feathers, that means that feathers probably weren’t a dinosaur innovation, but were first developed in a deeper ancestor on the family tree. We really have to reimagine the world of the Mesozoic as filled with many types of feathery, fluffy creatures on the land and in the sky.”
Benton expects some pushback from his colleagues, but he said his team’s research speaks for itself.
“Some will say [the pycnofibres] aren’t hairs or feathers, but shredded actinofrobrils (wing strengthening fibres)—we say they are not restricted to the wings but all over,” he said. “Some will say we are mistaken and none of them show any branching—we say: Have a look at the photos and specimens, and look for more specimens. Some will say feathers originated independently three or four times—pterosaurs, ornithischians, theropods—we say: Show us evidence that the pterosaur feathers are actually different in any way from these others.”
If his critics cannot provide answers to any of this, Benton said the simplest explanation is the single origin theory.
Manafzadeh said this study highlights some striking similarities between pterosaur pycnofibres and dinosaur feathers, but she’s not completely sure these structures truly had one evolutionary origin.
“This is because phylogenetic analyses like this one are very sensitive to how complete our datasets are—which is of course limited by what fossils we’ve found and how well-preserved they are,” Manafzadeh told Gizmodo. “It’ll be interesting to see how the results of this analysis change as more and more well-preserved, diverse pterosaurs are described and included in the dataset.”
Indeed, because this analysis was performed on just two specimens, it would be good to see similar fossils unearthed and studied, and by different teams. If Benton and his colleagues are right, there’s a creature somewhere in the fossil record that was the first to sprout feathers—somewhere in rocks dated to be at least 250 million years old. [Nature Ecology & Evolution]
Featured illustration: Yuan Zhang