The Brouhaha Over the 'Bald Pterosaur'

Whether or not pterosaurs had feathers has enormous implications for our understanding of dinosaur evolution

Ruth Schuster
Ruth Schuster
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Visions of a pterosaur with and without feathers
Visions of a pterosaur with and without feathers.Credit: Megan Jacobs / University of Portsmouth
Ruth Schuster
Ruth Schuster

Oddly, considering they’ve been dead for 65 million years, pterosaurs keep springing surprises. Among the latest wrinkles in pterosaur paleontology are the discovery of a new species with a beak so strange it was mistaken for a fish’s fin spine; and a smackdown over the flying reptiles’ body coating. Specifically: Did pterosaurs have feathers, as claimed in 2018? Or were they bald?

In 2018, a paper published in Nature Ecology and Evolution concluded that pterosaurs had feathers. Then a paper published in September 2020 rebutted that they didn’t. To which the original team replied: Yes they did. To which the rebutters reply: You’re not engaging in our arguments.

For us iggies out there in layman-land, feathers on a flying creature makes sense until we consider the bat. Anyway, so what if pterosaurs did or did not have feathers? Actually, the evolutionary implications for saurians are huge.

Let’s start with what we know, which is that a lot of dinosaurs had feathers, not only the ones that survived the extinction event and evolved into birds. Maybe feathering was the basal dinosaurian condition.

Pterosaurs, artist's impression.Credit: MARK GARLICK / Science Photo Lib

But pterosaurs were not dinosaurs. Pterosaurs and dinosaurs branched off from a common ancestor around 250 million years ago – they were cousins, in the sense that we and chimps are cousins.

So much for what we know. It is also widely accepted that pterosaurs had fluff, consisting of “pycnofibers”: sort of like primitive hair but not so deeply rooted in the skin.

The question, explains yes-feathers advocate Prof. Mike Benton from the University of Bristol, boils down to whether pycnofibers were proto-feathers.

If both dinosaurs and pterosaurs had feathers, it would strongly indicate that feathering evolved before they did, in their common ancestor. That is the huge implication. By that theory, nudity in certain subsequent dinosaurian lines was a secondary adaptation, like the whale lost its feet.

On the other hand, if pterodactyls were bald, or if pycnofibers weren’t proto-feathers but some homologue, it could indicate that feathers evolved in the dinosaurian set. So, which is it?

The eye of the beholder: Yes, feathers

Potentially supporting the theory of early insulation is a paper published this July in PNAS on a newly discovered species named Kongonaphon kely, which lived 237 million years ago and would have struck fear in the hearts of proto-cockroaches, maybe. It was all of 10 centimeters (4 inches) tall. The implication of Kongonaphon’s discovery is that the earliest dinosaurs were possibly little rat-sized things and the first pterosaurs were not large either.

Kongonaphon kely, a reptile near the ancestry of dinosaurs and pterosaurs.Credit: Alex Boersma

Add to that the foul weather of the Cretaceous and we now understand the need, if not the imperative, for body cover. It’s theoretical for now: no evidence of proto-feathers has been reported in the common ancestor so far.

Back to the yes-feathers 2018 paper by Prof. Baoyu Jiang of Nanjing University with Benton and others: They argue that some pycnofibers in certain fossil pterosaur specimens show branching typical of proto-feathers. The team not only concluded that they were feathers but four types of them. Also, they say, similar feathers appeared in dinosaurs.

“We say pterosaurs had feathers,” Benton spells out to Haaretz. “So feathers originated at the root of pterosaurs and birds, some 250 million years ago, and this means all dinosaurs had feathers – or could have feathers – and feathers originated 100 million years earlier than the first bird.”

He adds that he, and he thinks most other paleontologists, are dubious about the bald pterosaur idea because “in fact, the fossils show clearly they had whiskery feather-like structures all over their bodies.”

Pterosaur drawn with four different feather types on head, neck, body, and wingsCredit: @Reconstruction by Yuan Zhang

The eye of the beholder: Nope

However, the September 2020 paper in Nature Ecology and Evolution by David Unwin of the University of Leicester and Prof. David Martill of the University of Portsmouth challenges the identification of the feathers as such or even as pycnofibers.

They suggest that the observed pycnofibers/feathers in pterosaur fossils were actually tough fibers in the wing membrane: The ostensible feather-like “branching” reported by Jiang, Benton and the team could be the result of these fibers decaying and unraveling.

Bald-pterosaur advocate Unwin sums up that fossil evidence for feathering in pterosaurs is very weak. “Exceptional claims require exceptional evidence – we have the former, but not the latter,” he stated.

It bears qualifying that Unwin and Martill don’t suggest in their article that “pterosaurs were bald.” They write “no proto-feathers on pterosaurs.” However, the press release from the University of Portsmouth does go there: “Naked prehistoric monsters,” its headline announced, and the text spells it out: the two professors “believe they [pterosaurs] were in fact bald.”

Fossil of Darwinopterus modularis, a pterosaur.Credit: Didier Descouens

The eye of the bewildered: Feathers?

Following that barrage, the original yes-feathers team rebutted that the pterosaurs’ “whisker-like” pycnofibers show four distinct morphologies, not just one as assumed, and three show branching characteristic of feathers. Moreover, they insist, all four pycnofiber types are morphologically identical to structures already described in dinosaurs and birds, including at a chemical level. Ergo, they are consistent with feathers and therefore they evolved a cool 100 million years earlier than the feathers on Archaeopteryx.

Bald-pterodactyl advocate Unwin feels the anti-feathers rebuttal essentially restated the conclusions of the earlier paper rather than addressing the problems that were raised, he explains to Haaretz. “Critically, we pointed out the extreme rarity of records of purported proto-feathers,” he says. And among other things, the bald-pterosaur team noted a separate study on the relationships of dinosaurs and pterosaurs, which concluded that branched pycnofibers in pterosaurs are not the same thing as proto-feathers in dinosaurs. Ultimately, they believe the branched pycnofibers observed by Jiang, Benton et al are preservational artifacts and they “remain firmly convinced of this conclusion,” he tells Haaretz.

Benton explains that the body coat of pterosaurs has significance for our understanding of their metabolism. “People always assumed pterosaurs had an insulation coat, and this enabled them to be warm-blooded,” he says. If they were bald, they would be more hard-pressed to maintain body temperature – but in any case he doesn’t believe they were bald.

Asked how paleontologists reach different interpretations of fossil evidence, pro-feathers advocate Benton explains that to be scientific is to be skeptical. It’s all about methodology, and there are criteria for identifying feathers. Key to their identification of the pterosaurian integument as feathering is his team’s identification of melanosomes (organelles containing pigment) in the filaments.

Dinosaur fossil with clear evidence of feathers.Credit: Yosef Kiat

Feathers and hair and fur and pycnofibers contain melanosomes, nestling within the keratin (the protein that makes up all these). If the structures observed under the electron microscope aren’t pycnofibers or feathers as bald-pterosaur team Unwin and Martill suggest, but are wing tissue – then it would be made of collagen, not keratin, and collagen doesn’t have ensconced melanosomes, Benton explains, adding: “Full stop.”

The fossil record has a great many dinosaurs and birds with feathers by this time, and the structures in the pterosaur filaments are identical under the microscope and in ultrastructure, he says.

So did pterosaurs have feathers? Stay tuned. Meanwhile, here’s a picture of a pterosaur with the weird beak, reported by none other than Prof. Martill and colleagues (lead author Roy Smith).

An artist's impression of Leptostomia begaaensis with the weird beakCredit: Megan Jacobs, University of Portsmouth

Leptostomia begaaensis was a peewee by pterosaurian standards – about the size of a turkey – and its beak was so unusual that at first the paleontologist finding the fossil thought it was a fin spine from a fish. Really.

If anything, it looks less like a monster of our nightmares and more like a kiwi – the bird and not the fruit, that is. Actually, its skin may have looked like the fruit. As we said, stay tuned.