Guest post: How did pterosaurs extend their wing finger?

edina-daveThere are all kinds of aspects of palaeontology that in some ways we can only guess at how these things might have lived, functioned and behaved as living organisms. However one of the key aspects of science is the ability to make predictions and with careful use of analogy and homology (and of course the fossil record), we can try to work out some of those complexities that otherwise might leave us stumped. My former student Edina Prondvai and I have a new paper coming out in Historical Biology discussing how pterosaurs might have been able to extend that massive fourth finger and keep it stead during flight while minimizing energy expenditure. Edina takes us through it in this guest post:

The dominant characteristic of pterosaurs is the hyper-elongated fourth manual digit, that solely supported the extensive flight membrane. It is by far the longest lever arm along the leading edge of the wing among all actively flying vertebrates. Keeping this in mind it seems to be very odd that no one has paid special attention to the obvious energetic problem faced by pterosaurs: the extension of the enormous wing finger and its stabilization and control during flight. Thus the following questions went through my mind: Could such an extremely enlarged device have been operated exclusively by muscle force? If yes, how big should those muscles have been to be able to operate the wings properly? Is there enough space for them on the wing and shoulder bones at all? If not, how could pterosaurs have gotten around the problem and used as little musculature as possible to minimize the energy output (and the demand of higher neural control and to avoid significant mass increase especially in the distal wing that goes with it) but have still been able to fly? In the light of discoveries of giant pterosaurs such as Quetzalcoatlus or Hatzegopteryx this energetic problem of operating the wings during steady flight with muscles that require constant energy input and neural control to work becomes even more evident.

Despite their obvious evolutionary separation, the only extant flying vertebrates (birds and bats) managed to overcome the same problems in the same way (however, of a much lower magnitude due to the incomparable size-dimensions): biomechanical automatism has been built in their skeletal, muscular and connective tissue system.

The osteological investigation of several 3-D specimens of pterosaurs have made it clear to me that bones alone cannot provide solution for the former problems because there is no indication of a bone-based automatic mechanism in the wing function such as the geometric ‘drawing-parallels’ system in birds. Consequently the solution in pterosaurs must have involved soft tissues to a considerable degree. Since all powered flying animals have to face the same energetic problems here we got to the point where the extant life-style analogues must be used to fill in the gaps of our knowledge about the unpreserved soft parts and their possible significance in pterosaurs.

Based on the morphology, position, role and relative importance of ligaments and tendons in the automatic wing operation of birds and bats we were able to provide two possible models for the wing finger extension in pterosaurs.  In the first model we hypothesise the presence of a bird-like ‘propatagial ligament’ or ligamentous system which runs from the shoulder girdle to the wing finger. When the distance between the origin and insertion of these ligaments (hence the tension in them) increases by means of active elbow extension they automatically and passively perform and maintain the extension of the wing finger during flight and prohibit the hyperextension (and dislocation) of the elbow. In the second model, which has been derived from the first, pterosaurs have a more bat-like tendinous extensor muscle system on their forearm that shares the loads of wing finger extension with the bird-like propatagial ligaments. Both models fit with our existing understanding of the muscles and tendons of pterosaurs and where they attach to the various wing bones.

Wing extension model in pterosaurs. At rest (A) the elbox is flexed and the elasticity of the red tendon pulls the fouth finger into a retracted position. When the arm is extended (B) the tendon is stretch and the wing finger is pulled up into position and held in place, while preventing the elbow for being dislocated.

Wing extension model in pterosaurs. At rest (A) the elbox is flexed and the elasticity of the red tendon pulls the fouth finger into a retracted position. When the arm is extended (B) the tendon is stretch and the wing finger is swung up into position and held in place, while preventing the elbow from being dislocated.

Although merely hypothetical, both models provide a natural solution to avoid unnecessary exertion by: 1. reducing the muscle mass and by extension weight in the distal wing, 2. preventing hyper-extension of the elbow against drag, and 3. automating wing extension and thereby reducing metabolic costs required to operate the pterosaurian locomotor apparatus during flight. Future research is required both to test these models and to look for evidence to support them in the pterosaurian record, by they may help to reveal how an important part of pterosaur flight operated.

17 Responses to “Guest post: How did pterosaurs extend their wing finger?”


  1. 1 Zach Miller 15/04/2009 at 2:16 am

    Wonderful analysis! This is something I’ve privately wondered about for years. Do you think extension of one joint (say, the elbow) would automatically extend the other joints along the arm? I ask because that’s the case in many birds: folding the elbow results in the wrist folding back, and straightening the elbow results in the wrist straightening out.

  2. 2 Roger 15/04/2009 at 9:16 am

    Very cool. I’m also curious to know if torsional stresses at each of the joints in the fourth finger were particularly high, and if so, if there was a ligament system to counter that as well.

  3. 3 Edina Prondvai 15/04/2009 at 4:25 pm

    First of all, thank you very much for your comments!

    In response to the question of Zach Miller:

    When I first wondered about this question I only looked at it as a mechanical problem: I simply sketched the bones of the extended wing as sticks and found that (as it is mostly the case) the shortest way is the straight, so I connected the shoulder region with the proximal end of the “wing finger” to symbolize the structure that would be in the best position to extend the wing finger. That would do, I thought, so as next step I checked how it is in birds. I knew of course about the “drawing parallels” in birds which is a bone-based automatism that passively causes the complete flexion-extension action you mentioned above. But it’s something very different that pterosaurs surely could not do. That’s simply because the arrangement and shape of the wing bones and the articulation-design between them is not suitable for doing some kind of analogous action as birds do. I know this for sure as it was one of the things I checked in the first place. And that’s exactly what convinced me: if there was any kind of automatic reaction in the extension of the wing finger in pteros (which is to be expected for all kind of energetic reasons) it must have relied on soft tissues rather than on the mechanical linkage of bones. And surprisingly enough it turned out that birds do also have a soft-tissue based automatism in addition to their bone-based one (to the “drawing-parallels”) namely a propatagial ligament that runs exactly in the same topographical position as the straight line I drew on my “ptero-stick-wing” (between the shoulder girdle and the distal wing)! And as I went on with reading some more bird anatomy-literature I realized that this ligament (it is a system rather than one single ligament) has a very similar biomechanical function as I predicted for that straight line in pterosaurs! After that (to cut it short) I adopted this “bird-ligament” to pterosaurs and concluded that a lot of problems with wing finger extension can be solved this way. I did not extrapolate this automatism to the flexion process as it could have been operated only by muscle force since the tension in the stretched wing membrane and in the trailing edge structure, the profile drag during flight all acted against extension and for flexion of the wing finger. So in my opinion the main energetic problem of pterosaurs was not how to flex but how to extend the wing.
    Pfu, that was long. But I hope it was not “maunderings” and I’ve answered your question.

    In response to Roger’s question:

    Well, I’m quite sure there must have been very tough ligaments stabilizing those interphalangeal joints. However, I have no idea how effective they were at that. As I’ve experienced from flight engineers it must have been a great deal of work to counteract those forces acting on the wing finger during flight. They say the wing finger would strongly curve upwards and showed us a simulation of that. It was really convincing. Nevertheless, these things (pteros, dinos, etc.) did things I will probably never get how they did them (e.g. I cannot even imagine how giant pteros could have landed or fed from the water or how incredibly tendinous muscles sauropods must have had to carry that enormous body etc.). So as far as I’m concerned estimating the relative importance of soft tissues is always a guess-work but must always be considered. I’m sure there was a ligamentous system around the interphalangeal joints (as there is everywhere in the manus and pes of tetrapods) but how these extra forces coming along with their lifestyle could have been counterbalanced…I have absolutely no idea. But it would certainly be worth and interesting to reconstruct. Do you have a taste for it? :-)

  4. 4 Roger 15/04/2009 at 9:39 pm

    Edina- yes, the biomechanics of some of these massive Mesozoic critters boggles the mind! I’m looking at Mesozoic bird functional anatomy for my doctoral research, so any work on pterosaurs will have to wait :)

  5. 5 Edina Prondvai 16/04/2009 at 6:39 pm

    Roger – ohh…what a pity…we could have worked together :-)
    But your topic sounds very interesting to my ears. Could you specify it a bit more? And is/are there any paper/s out of your work yet? I’d really keen to read it/them!

  6. 6 Roger 16/04/2009 at 7:03 pm

    Could end up working on pterosaurs some day! Only 6 months into PhD. Have a paper describing a furcula from the Cretaceous of Australia coming out in the next issue of JVP, though it was sort of outside my PhD work…

  7. 7 ciavatti 24/04/2009 at 6:08 am

    Your model is interesting. A nice application of retraction of the claws of a cat. But how does he interacts with the movements of the patagium and actions of pteroide?

    • 8 Edina Prondvai 29/04/2009 at 4:14 pm

      The pteroid is not directly included in this wing finger extension action. Our models assume that the pteroid was connected to a tendon which ran from the shoulder region (e.g. from posterior neck muscles or shoulder muscles)to the medially pointing end of the pteroid and manipulated the propatagium accordingly. Although the reconstructed ligament runs in the propatagium, it is closer to the arm muscles and embedded in connective tissues and thus can work along with the anteriorly positioned leading edge tendon. I guess the leading edge tendon should have had an independent muscle control but could have co-operated with the ligament, as well. But what kind of patagium-movements did you mean?

  8. 9 Amin Khaleghparast 27/05/2013 at 10:43 pm

    Hello Dr. Dave Hone
    Thank you for your help and call to Dr. Mike Habib…..he respect to your call and answer to my Email….many thanks! he like my Dimorphodon skeleton specially my sketch is an effort related to hid theory for launch.

    http://paleo-reptiles.deviantart.com/art/Dimorphodon-skeletal-reconstruction-II-372726094

  9. 10 Amin Khaleghparast 27/05/2013 at 11:05 pm

    Dear friend, Dr. Dave Hone!
    Mark Witton never tell me his opinion about my sketch….although he have many art about Dimorphodon….Mike Habib told me about an Dimorphodon expert in your country…..Dr. Lorna Steel (from Isle Wight …. Polacanthus Isle)…..I have an Email about her:
    lorna.steel@pterosaur.net

    but after use, I never have any answer…..Do you have her Email or Gmail?

    I really need to her guide for correct my mistakes about my Dimorphodon skeleton….specially for giveing me a picture about 5 wrist bones of Dimorphodon (2 part of proximal carpals and three part of distal carpals) and pteroid and sesamoid….please help me….if you call Lorna Steel and Mark Witton and Wellnhofer for give me such pictures about Dimorphodon or telling me their expert opinion about my sketch. I do not way for getting their answers….they may pay attention to your request as a famous scientist!

    http://paleo-reptiles.deviantart.com/art/Dimorphodon-skeletal-reconstruction-II-372726094

    John Sibbick pictures are good but is not perfect for details of bones….

    my sketch is free access for every papers or books, website want speak about Dimorphodon….I think my sketch is a new effort about Mary Anning discovery and I am happy every pterosaur expert can help me for correct my sketch.

    • 11 David Hone 28/05/2013 at 12:36 pm

      Hi Amin,

      In general researchers do try and help out with such requests, but remember that we are very busy people with a lot of work to do, and we get a lot of requests like this. It’s simply not that easy or quick for each of us to try and find time for every request like this that comes in, and nor can you really ask five different people to help out on the same thing. I see from your page you have already had feedback from 8 different people and now you want more. I appreciate you want to get things right, but you can’t just keep bugging more and more people to get these answers, but need to better learn to find the information yourself.

      Certainly asking me to e-mail other people for you is pretty unreasonable, and if these people don’t want to reply, getting me to ask on your behalf is unfair on me and them.

      Just keep putting the hours in yourself to find the information yourself, that’s how this works.

  10. 12 Amin Khaleghparast 28/05/2013 at 11:22 pm

    my dear friend, Dr. Dave Hone!
    Thanks for your help….Dr. Lorna Steel respect to your call and connect me by Email….many thanks!

    I think Mark witton or others be interesting to speak about their love, Pterosaurs….but also, I understand bad economical condition in real life…….also, I have many economical problems. but my art is free access for every researcher need to them….also, I add name of my advisors beside my art for respect to their copyright…..Dimorphodon lived in England….therefore, you can ask yourself Why an Iranian biologist leave Molecular lab and try to make a scientific illustration about Dimorphodon for free…..my answer is “love”….I love Paleo-reptiles and I think Mark Witton, you and other friends have similar emotion…..I like to have a little role for help to next generation find better imagination about these animals….In Iran, We do not have any university filed about fossils…..therefore, I just try to be different of other Iranian people and start to an effort for improve condition…..I feel duty for this problem….more than 15 years of my life, I try to study paleo-reptiles with all of limitations in my country….If I perform every work about Molecular subjects until now, I was a famous researcher in my country….but I select other goal for my life…..Mary Anning was not scientist but Now, we know their effort was very valuable…..I forget many famous scientists with many papers and Noble prize but I remember Mary Anning, her Dimorphodon, and her love yet…..I hope scientists try to be like her in science instead of increase papers in an academic space…..I just want to continue her goal without any economical goal!

  11. 13 Amin Khaleghparast 29/05/2013 at 1:38 pm

    my dear friend, Dr. Dave Hone!
    I speak with Dr. Lorna Steel…she is very kind but she told me she is not a Dimorphodon expert…..I am surprised How a pterosaur from England (Dimorphodon) do not have any expert for analysis it….I am really surprised…..I do not want take your valuable time for research but if you know, please tell me name of Scientists or experts study Dimorphodon!

    it is just a friendly request!

    have a good time, Amin

    • 14 David Hone 30/05/2013 at 7:27 pm

      Well Kevin Padian wrote several major papers on this in the 1980s and did his PhD thesis on it, so a good amount of work has been done. Start there – there’s lots of photos and description.

  12. 15 Amin Khaleghparast 10/07/2013 at 10:41 am

    my popular scientist, Dr. Dave Hone
    First of all, Thank you for introduce Kevin Padian to me…you are a good friend for me :)

    http://www.lib.utexas.edu/books/britfossils/plates/txu-oclc-13370987-4-pterosauria-plate17_3000.jpg

    I look at Owen’s reconstruction on Dimorphodon…Now have a Question….between skull and claw of Dimorphodon, We see a small skull with mammals teeth…Do you see this skull?

    What is this small skull? a mammal as food or a baby Dimorphodon?

    Do any scientist have spoken about this small skull in this picture until now?

    • 16 David Hone 10/07/2013 at 10:56 am

      I have no idea, I’ve never seen the image before. The obvious thing to do is get hold of the original paper and read the figure caption / description.


  1. 1 Guest post: Rhamphorhynchus…again: Superprecocial “flaplings” or defenseless hatchlings? « Dave Hone's Archosaur Musings Trackback on 21/03/2012 at 7:39 am

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