Epic Flight Fail? Pterosaur Models Are Wrong, Says Study

By Gemma Tarlach | May 22, 2018 6:00 pm
An 1817 drawing of a juvenile pterosaur (then called a TKTKTK) shows a bat-like sprawl that researchers studying now say it impossible. (Credit von Soemmering T. 1817 U¨ber einen Ornithocephalus brevirostris der Vorwelt, Denkschriften der ko¨niglichen bayerischen Akademie der Wissenschaften, Math.-Phys. Klasse 6, 89–104.)

An early 19th century drawing of a juvenile pterosaur (then called a pterodactylus) shows a bat-like sprawl that is anatomically impossible. (More on this little fella below.) In fact, the authors behind a new study claim most reconstructions of these extinct animals in flight are inaccurate. But are they the ones who’ve got it wrong? (Credit von Soemmering T. 1817, Über einen Ornithocephalus brevirostris der Vorwelt, Denkschriften der königlichen bayerischen Akademieder Wissenschaften, Math.-Phys. Klasse 6, 89–104.)

Have paleontologists just been winging it? Up to 95 percent of the hip joint reconstructions of pterosaurs and their distant relatives, the most birdlike of dinosaurs, are anatomically impossible, according to new research that used a surprising source. But the study’s conclusions, counters a pterosaur expert, should be grounded.

Fleshing out an extinct animal from bones alone has always been paleontology’s greatest challenge, and mistakes have been made. But a paper published today makes the bold claim that the field has gotten aspects of flight, specifically hip mobility, wrong for a long time.

The authors say they’ve developed a new way to map how pterosaurs and some dinosaurs may have taken wing. It all starts with the common quail.

The common quail, shown here in a 1914 illustration, is not the most obvious pterosaur proxy. (Credit Wikimedia Commons)

The common quail, shown here in a 1914 illustration, is not the most obvious pterosaur proxy. (Credit Wikimedia Commons)

The small bird may be best known for being heard and not seen, but researchers looked at it and apparently thought “huh, that’s a good proxy for extinct ornithodirans.”

Right about now it’s worth reminding everyone that pterosaurs are not dinosaurs. Both pterosaurs and dinosaurs belong to the larger archosaur tribe, but so do birds (descended from one dinosaur lineage) and crocodiles, the archosaurs still with us today. The archosaurs are typically divided into the croc-like and the bird-like, the latter group sometimes called ornithodirans, a term not fully accepted in the field.

In fact, there is a lot of debate over which dead archosaurs fit where on the spectrum between crocodile and bird. For the purposes of this post, let’s go with the definition of ornithodirans that the authors of today’s paper seem to use, which would include birds, dinosaurs and pterosaurs. (Though it’s probably worth noting that the authors focus on maniraptors, the dinosaurs most closely related to birds, rather than the entirety of Dinosauria.)

Pterosaurs, meanwhile, often called flying reptiles, had tremendous diversity just within their order. They ranged from big as a bat all the way up to the famous Quetzalcoatlus, which was the size of some airplanes.

Witton, M. P., & Naish, D. (2015). Azhdarchid pterosaurs: water-trawling pelican mimics or “terrestrial stalkers”?. Acta Palaeontologica Polonica, 60(3), 651-660.

A 2015 illustration of one of the larger pterosaurs, with puny human for scale. (Credit Witton, M. P., & Naish, D. (2015). Azhdarchid pterosaurs: water-trawling pelican mimics or “terrestrial stalkers”?. Acta Palaeontologica Polonica, 60(3), 651-660)

Meanwhile, back in Dinosaurland, there have been a few non-bird species believed to be capable of some kind of flight, either powered or gliding, most notably Microraptor gui, the “four-winged dinosaur” from the Early Cretaceous, 120-plus million years ago. Researchers continue to debate just how flight-y Microraptors were, but that’s another topic for another day.

An artist's rendering of Microraptor. (Credit Fred Wierum/Wikimedia Commons)

An artist’s rendering of Microraptor. (Credit Fred Wierum/Wikimedia Commons)

Unlike birds (and closely related feathered dinosaurs that may have flown), pterosaurs evolved flight along a somewhat more bat-like pathway: Their wings were membranes attached to elongated finger bones. (In bats, the membranes stretch across the entire elongated “hand,” but pterosaur wings were attached to a single super-long fourth finger. Pinkie power!)

So, to recap, today’s study compares pterosaurs and some of the most bird-like dinosaurs, two diverse clans also very different from one another, to a quail.

About That Quail…

While much of the research on all these winged animals focuses on the winged bits — the forelimbs — the authors behind the new study zero in on the hip joints. They point out, correctly, that joints are integrated systems of bone, cartilage, ligaments, muscles, tendons, nerves and blood vessels — only one of which generally gets preserved in the fossil record: the bones, which tell only part of an animal’s story.

Dissecting a handful of adult quail, the team isolated the various parts of the hip joint, both bones and soft tissues, then mapped individual ranges of motion for each component, such as the ligaments or the bones. The authors were then able to layer different component maps, likening their system to charting countries and continents. You can show, for example, the continent of Africa with topography or with political boundaries or with both.

What they found, according to the paper, was that 94.72 percent of the hip joint poses that are possible based on bones alone are actually impossible when you add the constraints of soft tissue, particularly ligaments, that would have been present in the animal when it was alive.

While the authors noted that some of the bone-only poses they tested were extreme and probably would not be included in a reconstruction, they add that a lack of “consistent methodological constraints on hypothesized mobility” in the field doesn’t mean someone won’t try. The “bat-like” hip sprawl, for example, which has been proposed at various times for both pterosaurs and Microraptor, is possible with the quail’s bones but not when you include its soft tissue constraints.

As evidence that comparing a quail to a pterosaur is totally legit, the authors claim that the hip joints of birds, pterosaurs and maniraptoran dinosaurs (the dinos including and most closely related to birds, though there is disagreement on which species fall into this bunch) are “similar in several respects” such as the shape and positioning of the femoral head, or top of the thigh bone.

Flight Risk

I read the study a few times and, well, I had questions. A lot of them, about both its assumptions and conclusions. So I asked University of Leicester paleontologist David Unwin, a leading pterosaur expert not involved in the project, for his reaction to the paper.

“On the positive side, new data is always useful, and the basic approach of this study seems fine,” Unwin replied via email. “Understanding the anatomy/function of (living) birds and applying it to extinct birds/bird-like dinosaurs is reasonable, although the potential limitations of this approach needed much more analysis than given in this paper.”

That’s the good news.

“The pterosaur component of this paper is distinctly odd. It feels like it was bolted on later and in many respects is deeply flawed,” Unwin noted.

For example, Unwin continued, the bone structure around the hip joint — the pelvis and femur — is completely different for pterosaurs and birds, as several previous studies not mentioned in today’s paper have established. A recent study specifically on the musculature of the pterosaur pelvis is also ignored. Added Unwin: “There is no reason to suppose, therefore, that …the ligaments and soft tissues of pterosaur and bird hip joints are comparable, in which case the arguments made by the authors regarding soft tissue constraints on the orientation of the pterosaur femur are invalid.”

Unwin called the authors’ approach “baffling,” including their use of the 1817 juvenile pterodactylus illustration (seen at the top of this post) which was long ago dismissed as inaccurate. “The authors repeatedly refer to a ‘bat-like pose’ for pterosaur hind limbs. Why? This idea was abandoned decades ago,” he added.

There were other omissions, noted Unwin. The authors don’t acknowledge the debate over whether pterosaurs even were ornithodirans, nor do they address the hundreds of fossils — and thousands of pterosaur tracks — that contradict the study’s conclusions.

“Overall the paper seems completely outdated with regard to pterosaurs, using a terminology and understanding that seems rooted in the 1980s,” Unwin concluded. “A great deal more fossil material has been found over the last 35 years and ideas have moved on a long way – this paper hasn’t. Indeed one might ask why were pterosaurs included in this paper at all?”

A Diamond In The Ruffled Feathers

As in any field of science, in paleontology, hypotheses are put forth and tested and revised and, eventually, consensus emerges. Even the consensus may get scrapped and rewritten if sufficient, credible counterevidence turns up.

But the study out today is not going to rewrite any textbooks. It does offer a new way to map an extinct animal’s potential ranges of mobility, a method that may, once more broadly tested with a variety of proxies, provide a more accurate and detailed picture of how the animal actually got around. And that would be a terrific addition to the paleontologist’s tool kit.

The true value of the research is buried, however, in a strange refutation of dated ideas long ago refuted, and a curious crunching together of disparate animals.

As any eight-year-old can tell you, Quetzalcoatlus was no quail.

The study appears in Proceedings of the Royal Society B: Biological Sciences.

CATEGORIZED UNDER: Living World, top posts
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  • OWilson

    Articles about extinct flying giant pterosaurs, with “30 foot wingspans” have always had me wondering about how they actually got off the ground, given that gravity has not apparently changed since those times.

    The depiction of the human in the top photo seems to share my disbelief! :)

    From what we see today. the larger the bird, the longer the runway needed to take off and land. The larger the bird, the less flight capable it is.

    So, like with any science, it is good to review what we actually know for sure, and revise our theories accordingly. Good to see that!

    Thanks for the article!

    • Magmafrost13 .

      Pterosaurs didn’t take off the same way birds do. Im afraid Im not gifted enough with words to describe it, but I recommend looking up reconstructions of pterosaur launch cycles.

      • OWilson

        Maybe you missed the headline?

        Study says “Pterosaur Models Are Wrong”.

        So why would I waste my time?

        • Magmafrost13 .

          Is this a joke, or did you not read the actual article? The study’s comments on pterosaur physiology are sketchy at best. Thats what this article is about.

        • Lythronax argestes

          Don’t be dense. Are you really going to make such sweeping generalizations?

          • OWilson

            No, but I will continue to keep an open mind, and look forward to new information, in the “soft sciences”, lest I join those groups of “scientists” in their conventional wisdom, who continually give rise to headlines, like “Scientists puzzled!”, “Scientists scratching their heads”, and leaving their “settled science” dedicated followers with a little egg on their faces! :)

            Mother Nature, in her magnificence has evolved many methods of flying by insects, animals even plants, but I don’t recall “pole vaulting” as one of them.

            However I’m always willing to learn so if one of you could point me to a site where a study establishes that a pole vaulting, flying giant Pterosaur with a 30 foot wingspan, does not violate the principles of aerodynamics, I would be willing to suspend my skepticism!

            Thank you!

          • Joseph Daniel

            Look up any of several papers by Michael Habib and your questions will be answered. Be prepared to immerse yourself in real biomechanical math. Keeping an open mind is great. So is understanding where the field is currently at before saying you know better.

          • OWilson

            Old studies!

            This NEW study referenced in the article (Unwin) claims that the the assumption and premise of the older studies of Pterosaur bone structure is wrong.

            The debate continues! :)

            It’s all good!

        • Mike O’Sullivan

          I’d argue the headline is attention grabbing, considering the article ends with a tone of “the pterosaur stuff is fairly dubious”. The major problem really is that pterosaurs aren’t birds and are really not that comparable to them. Yes they both have wings but the entire skeletal structure is completely different. There isn’t a modern animal that serves as a strong analogy. I can certainly say the limitations of a quail hip don’t really reflect on the limitations of a pterosaur, the femoral and pelvic morphology is very distinct.

          • OWilson

            You say, ” There isn’t a modern animal that serves as a strong analogy.”

            So yes we are back to conjecture and theories.

            I tend to prefer newer theories than older ones.

            Ceratinly the awed audiences of Hollywood depictions of Dinosaurs, and Pterosaurs will be a little disappointed,

          • Lythronax argestes

            New theory hot off the presses: dinosaurs are actually made up and never existed. Are you gonna buy that too?

            New is not better.

          • OWilson

            I’ll leave you to your own theories.

            What a person believes is a personal choice.

          • Lythronax argestes

            Sorry, scientific consensus is scientific consensus.

            Or do you believe in a young earth too?

          • OWilson

            Strawman alert!

          • Lythronax argestes

            Pot, kettle…

    • Joseph Daniel

      Large birds need a large runway to get enough lift under their wings because they can”t jump high enough. Pterosaurs, according to Habib etal., use their long wings to basically pole vault into the air. Thus, they can get airborne easier than large birds.

      • OWilson

        No one obviously has ever seen these huge animals fly, so that is still conjecture in a rapidly changing science.

        The article indicates that the formerly accepted bone structure of these giants has been found recently to be erroneous.

        That would tend to negate earlier explanations of just how they were supposed to fly?

        • Joseph Daniel

          Conjecture? I do not think that word means what you think it means. It isn’t just guesses. I am talking about serious study of the anatomy and biomechanical possibilities. Pterosaurs were biomechanically incapable of taking off like birds. The studies have shown that the forelimb pole vaulting approach is the best proposed model of pterosaur flight. You should really read something from Unwin published since the 70s as he is not opposed to it either.

          You might also notice that the new article is not accepted by current pterosaur experts, for one reason because it disproves ideas discarded long ago.

          • OWilson

            “New” theories are rarely immediately “accepted” conventional wisdom “experts!”

            But that’s how science marches forward!

          • Joseph Daniel

            Well aware of that. But we are not talking about the old guard not accepting something new here. What we are talking about here is the old guard saying the paper is saying that hypotheses that were discarded decades ago are wrong. They already knew that and have moved on. Science has already marched on.

          • OWilson

            New evidence and new interpretations of that evidence, is coming up at a rapid pace.

            Best to keep an open mind!

          • Joseph Daniel

            Keeping an open mind is good, I agree, but that doesn’t mean blindly accepting everything that is new. Not all hypotheses are equal. They still need to be critically evaluated and flaws elucidated so they can be fixed. When experts point out flaws, those flaws need to be examined in light of the evidence. As is often said, keeping an open mind is good, so long as it is not so open your brain falls out.

  • http://www.reptileevolution.com David Peters

    Testing a wide gamut of pterosaur outgroup candidates reveals that pterosaurs are neither archosaurs nor archosauriforms, but lepidosaurs (from a new clade nesting between Sphenodontia and Squamata). Pterosaurs close to Padian’s Dimorphodon had more erect femora based on the head/shaft angle. Others had sprawling hind limbs, like those of modern lizards (Chlamydosaurus) capable of bipedal locomotion. Lifting the forelimbs off the substrate freed the hands to start flapping. Reducing the need to undulate freed pterosaur ancestors from Carrier’s constraint. More details, images and links here: https://pterosaurheresies.wordpress.com/2018/05/24/quail-hip-joints-are-not-good-models-for-pterosaur-hip-joints/

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