Dr. David Unwin from the University of Leicester and University of Portsmouth’s Professor Dave Martill believe Mesozoic flying reptiles called pterosaurs had a relatively smooth skin without any covering.
An artist’s impression of a bald pterosaur and a feathered pterosaur. Image credit: Megan Jacobs, University of Portsmouth.
Pterosaurs were Earth’s first winged vertebrates, with birds and bats making their appearances much later.
They thrived from about 210 to 65 million years ago, when they were wiped out by the asteroid that also doomed the non-avian dinosaurs.
It is widely held that pterosaurs were covered with hair-like structures called pycnofibers.
In 2018, Nanjing University paleontologist Zixiao Yang and colleagues proposed that some pterosaur pycnofibers were branched, exhibiting ‘brush-like’ and ‘tuft-like’ morphologies.
Going further, the team compared the branched pycnofibers to protofeathers, previously reported for several dinosaurs, and argued that they share a common origin.
“Feathered pterosaurs would mean that the very earliest feathers first appeared on an ancestor shared by both pterosaurs and dinosaurs, since it is unlikely that something so complex developed separately in two different groups of animals,” Dr. Unwin and Professor Martill said.
“This would mean that the very first feather-like elements evolved at least 80 million years earlier than currently thought.”
“It would also suggest that all dinosaurs started out with feathers, or protofeathers but some groups, such as sauropods, subsequently lost them again — the complete opposite of currently accepted theory.”
Dr. Unwin and Professor Martill propose that the branched pycnofibers in pterosaurs are not protofeathers at all, but tough fibers which form part of the internal structure of the pterosaur’s wing membrane, and that the ‘branching’ effect may simply be the result of these fibers decaying and unraveling.
“The idea of feathered pterosaurs goes back to the 19th century but the fossil evidence was then, and still is, very weak,” Dr. Unwin said.
“Exceptional claims require exceptional evidence — we have the former, but not the latter.”
“Either way, paleontologists will have to carefully reappraise ideas about the ecology of these ancient flying reptiles,” Professor Martill added.
“If they really did have feathers, how did that make them look, and did they exhibit the same fantastic variety of colors exhibited by birds.”
“And if they didn’t have feathers, then how did they keep warm at night, what limits did this have on their geographic range, did they stay away from colder northern climes as most reptiles do today.”
“And how did they thermoregulate? The clues are so cryptic, that we are still a long way from working out just how these amazing animals worked.”
The team’s paper was published in the journal Nature Ecology & Evolution.
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D.M. Unwin & D.M. Martill. No protofeathers on pterosaurs. Nat Ecol Evol, published online September 28, 2020; doi: 10.1038/s41559-020-01308-9
