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
This ancient ‘hairy dragon’ may have sported primitive feathers
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’s 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 also could 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.”
Although 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.”
doi:10.1126/science.aaw4030
