(CN) – The origin of feathers occurred 70 million years earlier than previously thought, according to an international team of paleontologists.
Publishing their findings Monday in the journal Nature Ecology & Evolution, the team from Nanjing, Bristol, Cork, Beijing, Dublin, and Hong Kong show that pterosaurs – a flying reptile – shared four kinds of feathers with the dinosaurs they lived side by side with between 230 and 66 million years ago.
Two major groups of dinosaurs – the plant-eating ornithischians and the bird ancestors theropods – also show four kinds of feathers: simple filaments or hairs, bundles of filaments, filaments with a tuft halfway down, and down feathers.
It has long been known that pterosaurs had some sort of furry covering often called 'pycnofibers', but until now scientists presumed the covering was fundamentally different from that of feathers of dinosaurs and birds.
"We went to Inner Mongolia to do fieldwork in the Daohugou Formation,” lead researcher Baoyu Jiang of Nanjing University, China, said.
"We already knew that the sites had produced excellent specimens of pterosaurs with their pycnofibers preserved and I was sure we could learn more by careful study."
Zixiao Yang, also of Nanjing University, described the opportunity he and his colleagues had to work on some amazing fossils.
"I was able to explore every corner of the specimens using high-powered microscopes, and we found many examples of all four feathers," Yang said.
Maria McNamara of University College Cork, Ireland, added that while some critics suggested the existence of only one simple type of pycnofiber, their studies show that different feather types are real.
"We focused on clear areas where the feathers did not overlap and where we could see their structure clearly. They even show fine details of melanosomes, which may have given the fluffy feathers a ginger color," McNamara said.
Birds have two types of advanced feathers used in flight and for body smoothing, the contour feathers with a hollow quill and barbs down both sides. These are found only in birds and the theropod dinosaurs close to bird origins. Other feather types of modern birds include monofilaments and down feathers that are seen much more widely across dinosaurs and pterosaurs.
Researchers say the armored dinosaurs and the giant sauropods probably did not have feathers because they were blocked just as hair is suppressed in whales, elephants, and hippos. In pigs, piglets are covered with hair like puppies but hair growth is blocked in adulthood.
Professor Mike Benton from the University of Bristol's School of Earth Sciences said the group’s evolutionary analyses showed clearly that the pterosaur pycnofibers are feathers, just like those seen in modern birds and across various dinosaur groups.
"Despite careful searching, we couldn't find any anatomical evidence that the four pycnofiber types are in any way different from the feathers of birds and dinosaurs. Therefore, because they are the same, they must share an evolutionary origin, and that was about 250 million years ago, long before the origin of birds," Benton said.
This discovery has amazing implications for our understanding of the origin of feathers, but also for a major time of revolution of life on land, according to Benton.
"When feathers arose, about 250 million years ago, life was recovering from the devasting end-Permian mass extinction,” he said.
By then mammal ancestors had hair, and the pterosaurs, dinosaurs and relatives had likely acquired feathers to help insulate them as well. Independent evidence shows that land vertebrates, including the ancestors of mammals and dinosaurs, had switched from sprawling to upright gait, had acquired different degrees of warm-bloodedness, and were generally living life at a faster pace, researchers say.
"The hunt for feathers in fossils is heating up and finding their functions in such early forms is imperative,” Benton said. “It can rewrite our understanding of a major revolution in life on Earth during the Triassic, and also our understanding of the genomic regulation of feathers, scales, and hairs in the skin."