This pigeon-size pterosaur, which lived roughly 160 million years ago, had branched filaments on its skin that resemble feathers.
Yuan Zhang/Nature Ecology & Evolution
By Gretchen Vogel
Ptersoaurs—flying reptiles, some as big as giraffes—were the first vertebrates to develop powered flight, more than 200 million years ago. Scientists have long known that these distant cousins of dinosaurs had fuzzy, furlike fibers on their skin. Now, a new study suggests those fibers might have been a kind of primitive feather. That would upend the assumption that certain dinosaurs—including modern birds—were the only ones to develop feathers.
Scientists have known since the 1800s that pterosaurs were covered in short hairlike filaments called pycnofibres, which probably formed a fuzz or furlike covering. But no one knows exactly what these fibers looked like when the animal was alive.
Michael Benton, a paleontologist at the University of Bristol in the United Kingdom, paleontologist Baoyu Jiang of Nanjing University in China, and their colleagues examined fossils of two pigeon-size pterosaurs found at the Yanliao Biota in northeastern China. The site is known for its exquisitely preserved fossils from between 165 million and 160 million years ago, including some of the earliest birds. The two pterosaurs caught the researchers’ attention because they were “exceptionally hairy,” Benton says, with unusually well-preserved pycnofibers.
Luckily, the specimens, now stored at Nanjing University and the Chinese Academy of Geological Sciences’ Institute of Geology in Beijing, had not been coated with the protective lacquer applied to many fossils that sometimes obscures details and prevents chemical analysis. Careful examination under a microscope showed they sported four types of filaments: a hollow, slightly curved hairlike filament—the standard pycnofiber—that covered most of the pterosaurs’ bodies; bushy tipped filaments on the neck, base of the tail, and parts of the legs; a differently shaped filament with bushy fibers extending from the middle on the head; and, finally, on the wing membranes of both animals, filaments that seemed to be tufts of branched filaments. “The correct term for a branching thing that grows out of the follicle of the skin is a feather,” Benton says.
These feathers, like down on modern birds, might have helped the warm-blooded animals regulate their temperature, the team reports today in Nature Ecology & Evolution. They could also have played a role in flight aerodynamics, coloration, and may have enhanced the animals’ sense of touch, the authors say. An artist’s rendering of the pterosaur based on the new study looks like a fluffy baby dragon—or perhaps a relative of Buckbeak, the hippogriff from the Harry Potter movies.
Pterosaurs are only distantly related to dinosaurs and birds, the other animals known to have had feathers. If the newly found structures really are a type of feather, Jiang says, that means the common ancestor of birds and pterosaurs may have had them, which would move the origin of feathers back from 175 million years ago to roughly 250 million years ago. It would also suggest that a broad variety of dinosaurs—including plant-eaters not directly related to modern birds—might have also had featherlike structures on their skin. (Some researchers have reported featherlike filaments on these dinosaurs, but those claims are vigorously debated.)
But David Unwin, a paleontologist at the University of Leicester in the United Kingdom, thinks the branched filaments are more likely to be structural fibers called actinofibrils that were part of pterosaurs’ wing membrane. “Whenever we have soft tissue in pterosaurs, wing fibers are always there,” he says. The branches, he says, could be decaying wing fibers that have started to unwind and fray.
Jiang, Benton, and their colleagues say detailed studies of the filaments support their theory. Using a scanning electron microscope, x-ray spectroscopy, and infrared spectroscopy, they discovered the structures were likely made of keratin—the protein that forms hair and feathers—and they found structures that looked like melanosomes, organelles that contain melanin and are also typically found in hair and feathers. (The melanosomes’ chemical composition suggests the fibers were likely brown or red, not black.) But actinofibrils could also have contained keratin and melanosomes, Unwin says.
From a genetic perspective, early evolution of primitive feathers isn’t so far-fetched, Benton says. The genes that control the growth of hair, feathers—and scales—are very similar, he notes. “A chicken has feathers and scales on its legs, and a rat has scales on its tail.”
While skeptical about the group’s interpretation, Unwin says the study will help scientists get closer to understanding pterosaur skin. “These are two really great specimens,” he says. “And the imaging studies they did were really, really good. It’s very helpful to have the data.”
Source: Science Mag