That troublesome pteroid

Anyone who has been keeping up with pterosaur research in the last few years will have spotted the various exchanges going on over the pteroid bone. I am not sure I ma giving anything away or bringing something private out into the open air when I ‘reveal’ that the pterosaur community is petty small and there are some fairly big disagreements that have been going on for what seems, to a relative newcomer, like decades and this is simply the latest one. However it is one of great interest as this relatively innocuous bone is actually very important in pterosaur research.

“But what is a pteroid?” I (possibly) hear three or even four of you (possibly) ask. Come this way and all will be (possibly) revealed (possibly)….

pteroid1The pteroid is a small bone that articulates with the pterosaurian wrist and helps control the propatagium (the ‘front wing’ that sits in the crux of the arm). There are quite a few different types of pteroid ranging from a simple spike, to a long rod, and even a few with a 90 degree twist in the base like a bendy drinks straw. Thanks to a lack of direct pterosaurian ancestors in the fossil record we are not sure where the pteroid comes from, it’s either a highly modified wrist bone, or a ‘neomorph’ (that is a new bone that has evolved exclusively in pterosaurs) but it’s actual identity is rather irrelevant to the key question. Here is a nice picture of a pteroid in a specimen of Pterodactylus (black arrow) with the propatagium (red arrow) lying between the wrist (white arrow, where the pteroid articulates) and the upper arm (on the right).

And that question is “In what direction did the pteroid point? To the front or to the middle?” (or more technically, anteriorly or medially). Though you might want to add to that “And who cares? Is it really important?”Well a lot of us (OK out of pterosaur researchers) care and in a few ways it is important, but mostly it is an issue because the direction of the pteroid profoundly affects the way in which pterosaurs could have flown, with the two different positions offering a very different flight profile. A forward pointing pteroid (especially one that could be flipped to point downwards) has been suggested several times in the literature on the grounds that it would massively increase the size of the propatagium and enable the wing camber to be significantly increased which in turn would increase the lift available to the pterosaur, providing more control and great efficiency, something that would be especially advantageous to some of the 12 and 13m wingspan giants of the end Cretaceous.

However, despite the intuitive appeal there was no real evidence for this, and certainly no figures to back up the idea until some recent computer model based research suggested that a forward pointing pteroid could add up to 30% lift when compared to a medial pteroid / small propatagium. What’s more, it was also suggested just how the pteroid could articulate on the complex pterosaurian wrist to produce the necessary effects. Suddenly the idea was a lot more credible than before and actually had some data to back up the concept, but as ever this was not the whole story at all.

For a start, not everyone agreed that the proposed articulation was not even necessarily possible and in fact the pteroid could only have articulated at a point that would make it point medially. (I’ll not go into the details because it gets really, really messy, but essentially you have several of ‘dips’ in the various wrist bones where something like the pteroid could articulate, and both a pteroid and a small bone called a sesamoid that needed to fit – which one went where, and how?). Secondly, the proposed orientation would put huge stresses on the pteroid and in several species it is incredibly long and thin or even sinusoidal and there was no way it could have supported the forces suggested to be going through it (and it may have also torn the propatagium with a pointed tip). Thirdly at least some pteroids simply couldn’t orientate forwards (not least those with a bend in the middle) so at the very least if the forward interpretation is true for some we will still have to have medial ones for others. So how can we resolve this issue?

Well the obvious response is to check the fossil record (naturally) and of course to bear in mind that just because something is possible or apparently good does not mean that it happens (i.e. a forward pointing pteroid would massively increase lift, but that does not mean pterosaurs necessarily evolved it). Sadly as you might have guessed the fossil record is not as clear cut as one might expect on the issue – surely sooner or later you will just have a wrist preserved with the pteroid jammed in one socket and the sesamoid in another, problem solved. Well, no and when you think about it for a rather obvious reason. The pteroid is of course bound up in the propatagium (a muscular sheet of tissue) and furthermore no matter its orientation would have been held in place by a bunch of tendons and ligaments, and possibly various muscles as well. That means when the animal dies and muscles rot or contract and ligaments and tendons shrink as they dry the pteroid gets yanked out and moved. It is only ever found in what appears to be a natural articulation in the ‘roadkill’ 2D specimens from places like the Solnhofen of Germany such as the one pictured. Here it might well be articulated, but since it is flat you still can’t see exactly where it joins the wrist or how, and the animal is small too that does not help.

If you check various abstracts appearing in various palaeontological meetings over the last few years (SVP, SVPCA and EAVP) you will see a swathe of pteroid descriptions moving back and forth between several researchers in addition to some major papers either published or making their way through the review process. Currently the consensus seems to be swinging back in favour of a medially facing pteroid and at the least this must have been true for some animals (those with exceptionally thin pteroids, or crooked ones). The real question now is exactly how and where that articulation occurred on the wrist, but this one is set to run for quite a while yet. It seems odd that so much attention and interest could be generated by such a small bone, especially one so often preserved so well. As ever, new finds are coming to the rescue with better preservation and new information available but it will still be some time before the dust settles on this one. I’ll keep you posted. In the meantime, you can try Chris Bennett’s pteroid challenge .

48 Responses to “That troublesome pteroid”

  1. 1 Zach Miller 08/11/2008 at 3:56 am

    Well, I thought Unwin’s SVP presentation was odd for a couple of reasons, but mostly because the finger-like sesamoid bone is apparently no longer the origin point of the pteroid. Instead, the pteroid sits between two proximal carpals while the sesamoid just sits there? What’s the purpose of that sesamoid? It looks like there’s an articular facet RIGHT ON TOP OF IT, but apparently not. It ended up looking like pterosaurs have TWO pteroid bones, one long and thin, one short ‘n’ fat (the sesamoid).

    I came away unconvinced, and still subscribe the the idea that the pteroid bone points toward the shoulder, articulates with that wierd sesamoid, and anchors a large ligament for the propatagium. You know, just as 99% of the pterosaur wrists (that I’ve seen) show.

    Also, just because a computer model simulates a better wing area if the pteroid is oriented medially doesn’t actually mean anything. Organisms are not usually “perfected.”

  2. 2 ScottE 08/11/2008 at 4:06 am

    “Organisms are not usually “perfected.””

    No, not usually, but yet, sometimes, they are in fact just about that. Feathers are a prime example. For surface-area to weight and structural integrity, you’d have a hard time coming up with something that tops the feather as an airfoil component.

    (We need to get together and talk about this stuff for Gina’s class. It might make for interesting discussion…)

  3. 3 Christopher Collinson 08/11/2008 at 6:59 am

    Firstly, the “short fat sesamoid” is not a sesamoid, its the medial carpal.

    A Sesamoid is a bone thats is found embedded in a tendon at the point where the tendon passes over a joint. They protect the tendon as it transfers the force generated by muscle around the joint, as well as increasing the mechanical advantage of the tendon. Your knee cap is a sesamoid and they are also found in the wrist and foot. The sesamoid everyone in pterosaur research is talking about is “Sesamoid B,” a little circular element that according to Bennett and a majority of the fossil evidence, slots into the notch/articular surface at the tip of the medial carpal. This also happens to be where Wilkonson and others have/had in the past reconstructed as the position where the pteroid articulates. Bennett reconstructs the point of articulation as being on the medial surface of the medial carpal.

    On David Unwin’s SVP2008 talk; his abstract appears to be summery of and supporting Matthew Wilkinson’s work re: broad propatigum, anteriorly directed and mobile pteroid articulating to the anterior surface of the medial carpal. However, from the brief mentions here and there I gather, it seems, that his actual talk was quite different and that he now advocates a pteroid articulating with the proximal syncarpal. This is something that wouldn’t really surprise me as Ive noted a close relationship between the two in some specimens. Can someone who was actually present for his talk straighten this out for me?

  4. 4 Zach Miller 08/11/2008 at 8:25 am

    Christopher, I saw the talk, but I’d really need to be able to draw it. I think better in pictures than verbal descriptions. But I’ll try. This is the line drawing that Unwin presented as how the pterosaur wrist looks: The medial carpal is pointing forward, looking sort of like a bizarre finger bone, on top of the distalmost carpal bone. In between the two main carpal bones sits the pteroid bone, also pointing forwards, although he stressed that, at rest, the pteroid could lay down, pointing toward the body. I didn’t see any evidence of an actual joint there, but whatever.

    The “ouline” of the propatagium goes from the base of the clawed fingers to the outstretched pteroid (completely engulfing the medial carpal in the propatagium) to the shoulder.

    The propatagium did not end up looking like a triangle, though, but a curved line, as though some mysterious tissue were acting upon the distal end of the propatagium to gently curve it upward. Again, a picture is worth a thousand of these things. I’d like to post my take of it on my blog, but the embargo forbids it (ARGH!).

  5. 5 David Hone 08/11/2008 at 10:05 am

    One thing to add is Dave Unwin largely changed his position from the time he submitted the abstract to the time he gave his talk. His words to me yesterday on the subject were roughly “yes, I got it all backwards” so dn’t use this year’s abstract as a reference for where he currently stands on the issue.

  6. 6 Christopher Collinson 08/11/2008 at 12:36 pm

    Hmm, ok. Unwin’s new arrangement sounds pretty much like Bennett’s except he has the pteroid floating rather than articulated with the medial face of the medial carpal.

    This is quite the about face from Unwin, he must have seen something pretty interesting.

  7. 7 Nathan Myers 14/01/2009 at 5:35 pm

    Congratulations to Dave Unwin for his volte-face. It takes a big man, etc.

    Couldn’t one or other of you-all take an Engineering Statics course? There’s no way a bone that thin could counter any bending stress. About all it might be good for is to help damp down flapping in the wing membrane.

  8. 8 David Hone 15/01/2009 at 6:01 pm

    Well why not speak to Wilkinson or Templin or Bramwell?

  9. 9 David Peters 17/12/2009 at 3:06 am

    There’s something about the pteroid articulation and orientation in the latest issue of JVP (Dec. 2009)along with a genesis hypothesis.

  10. 10 Doug Henning 17/12/2009 at 10:46 pm

    Hmmmm….David, might you have written it? You have a good point about the carpal articulation proximal-to-sesamoid but I cannot follow you down the primrose path to prolacertilian pterosaurs. Articulation may initially have been along the carpals and, as the pterodactyloids developed, the derived condition of the wafer-thin pteroid disarticulated and merged more into the propatagium, becoming structurally less necessary for flight control. Has this been considered?

  11. 11 David Peters 18/12/2009 at 8:30 pm

    Wafer thin?
    Merged into the propatagium?
    Less necessary for flight control?

    Where does all this data come from?

  12. 12 Jack 18/03/2010 at 4:19 am

    How about a simple explanation.
    The thumb right down to the wrist fused?

  13. 16 David Peters 19/03/2010 at 1:14 am


    Evidence always helps. For instance, you might want to indicate how your digits II-V came to become identical to the standard I-IV in terms of joint number, unguals, etc.

    What would happen to your hypothesis if a vestigial digit V appeared on the lateral side of the big metacarpal IV? Just wondering.

    When in the family tree of pterosaurs or pre-pterosaurs do you propose your proposed changes happened?

    These are the support items you must bring to your argument. Make it so.

  14. 17 Jack 19/03/2010 at 4:48 am

    I am working with the idea that the pterodactyl evolved from the bat or they shared a common ancestor. I have been studying this – looking at every aspect of it.
    So I do not relate the pterosaur finger phalanges to a reptile hand. I relate it to the fingers and the phalanges of the bat.
    It is not easy to get info on the phalanges of the fingers of the bat. If anyone has info on the phalanges of the fingers of the bat I am very interested.
    And I am working with the idea that the pteroid is the thumb and it has been fused.
    Also it may be that ancient bats had slightly different finger configurations and may even have differed from one type to another.

    • 18 Jack 19/03/2010 at 5:05 am

      Figures 8, 9 and 11 in this link have some info on bat phalanges.

    • 19 David Hone 19/03/2010 at 8:10 am

      That just will not work, full stop. GO and look at the bones IN DETAIL and you will see the unbeliveable huge number of changes to go from a bat to a pterosaur. It’s not a question of ‘just’ changing the hands – pretty much every detail in the skull and skeleton is different. We know how the muscles groups fit together in pterosaurs to power flight and it’s very different to that of bats (since they are mammals), bats have soft bones and pterosaurs don’t, bats can echolocates and pterosaurs can’t (indeed their brains and ears are built very differently), pterosaurs have the classic set of diapsid fenestra in the skulls that bats lack, pterosaurs have airscacs, bats have a clacar, pterosaurs have a pteroid, their teeth are rooted differently, their body coverings are different, bats lack actinofibrils etc. etc. etc.
      I find it impossible to accept that you have looked at any of this in a fraction of the detail required to understand this problem. Cuvier was talking about this problem in the 1700’s and was able to show why pterosaurs were not bats then, and science has moved on just a wee bit since. I suggest you start there and not bother with posting unsupportable nonsense on here. Read some books, or better yet, read this:

      • 20 Jack 19/03/2010 at 8:16 am

        Boy it did not take long for the word “nonsense” to appear.
        If you do not about the phalanges in the bat, just say so. I don’t need the rest of the baloney.
        I can talk to all the issues of the anatomy.

      • 21 David Hone 19/03/2010 at 8:26 am

        Well, if you have read anything in detail of any part of the anatomy of pterosaurs and bats it should be more than obvious that they are incredibly different. There is good reason that researcher have considered pterosaurs as reptiles for 250 years and bats as mammals for several thousand years. If you are going to try and overturn that and draw me (or any researcher) into a serious discussion of this you need to demonstrate that you know what you are talking about. I get enough cranks and creationists on here to want to avoid any others.

        I do know about bat phalanges having studied bats before. Dont’ cover your ignorance by suggest that I am ignorant. I gave you a huge raft of absolute fundamental differences between the two groups and you simply suggest I lack a knowledge of the details of one aspect of one small part of the anatomy of one clade.

        If you can talk about all the issues of anatomy, great, well done. I’m glad you are doing the research and reading. However, *I* don’t want to talk about it. Find someone who does, and try and get a paper published if your evidence is good enough.

  15. 22 David Peters 19/03/2010 at 8:32 am

    If we were a wee bit closer to April 1, I’d say you were being pranked, David.

    Then again… oh, well. Maybe, as you suggested, not worth the bother.

    • 23 Jack 19/03/2010 at 10:01 am

      Before we even get started the minds close.
      Oh well.
      If bat phalanges are beyond you then there is not much I can expect from you.
      But go ahead – tell me again that you know it but you are just not going to say. No problem.

      • 24 David Hone 19/03/2010 at 10:17 am

        I didn’t talk about closed minds, I suggested you were ignoring the evidence, or hadn’t read the evidence. Knowing bat phalanges really quite well (as I have already said) is ultimately irrelevant to the argument. We do not classify organisms according to single isolated characters, so even if bat phalanges were indistinguishable for pterosaur ones (which they aren’t) it would not make bats pterosaurs or vice versa.

        Do you know about the molecular and crystalline structure of bat phalanges? They are rather different to other vertebrate bones, and indeed the histology is diganosably different to pterosaur phalanges, they also lack pneumatopores and the ‘wing groov’ that you see in pterosaurs. So see, i do know about them, and more than can be gleaned from a single online parataxonomy document. As noted above this is not the only issue and I make a huge list of other things you will have to ‘solve’ if you want to tie these together, arguing about my supposed ignorance of bat phalanges does NOT invalidate all of my points.

        Like i say, I’m satisfied with my own education and information and that of tens of thousands of scientists working over hundreds or years. If you disagree, fine, go and get the evidence and publish it and show the world. Scientists welcome discussion. However, we do this based on evidence. Just saying you want to discuss things doesn’t count. I have better things to do with my time and in any case, while I have worked on bats and do know a fair bit about them, I have better things to do with my time that discuss their realtionships with pterosaurs (or otherwise). Why not do me the courtesy of accepting that actually i am quite knowldgeable on the subject, but don’t want to discuss it with you, here, now? That’s hardly unreasonable, this is my blog after all. There are plenty of forums out there for this, not least the actual scientific literature itself, research meetings, and online discussion groups.

        So save us both the hassle since I am simply reasonably asking that you not clutter up these boards with unsupported claims or accusations of ignorance on my part. I’m happy and indeed willing to discuss anatomy. I’m not happy and unwilling to have to expend great effort and energy showing something to be fundametally incorrect at every level that could be gained with 10 minute of reading of any decent evolutionary textbook. If you really are genuinely interested, go get a copy of Dave Unwin’s pterosaur book, or Wellnhofer’s one, or e-mail a few researchers and ask for some papers. But here I am politely, if forcefully, asking you not to bug me and this site with this kind of thing.

      • 25 Nick Gardner 19/03/2010 at 2:23 pm

        Jack, why are you ignoring all other points of evidence and only looking to gross similarities between phalanges (not even of the same digit…)?

        If anything is close-minded, I’d say that is…


  16. 26 Jack 19/03/2010 at 8:20 pm

    Nick, we have to start some place.

  17. 27 Nick Gardner 19/03/2010 at 9:59 pm

    That’s great, but in doing so, you’re ignoring all the bodies of evidence that clearly point to the non-affinities of bats and pterosaurs….

    • 28 Jack 19/03/2010 at 10:13 pm

      Nick, let’s start with the bat finger phalanges and go from there. As I said we have to start somewhere.
      After that, you can choose the next characteristic to look at, if you like.
      But we have to start somewhere or we will never start at all.
      Do you know the finger phalanges of the bat?

      • 29 David Hone 19/03/2010 at 11:05 pm

        It matters not if Nick knows bat fingers or not. I do, as I think I demonstrated above, and indeed that they are very different given the otherwise conservative nature of tetrapod digits. I also know the rest of the anatomy and the fossil record too. With something like this you don’t have to start ‘somewhere’ you have to start ‘everywhere’. As I have noted already we don’t work from single characters but all of them. Taxa are not defined by single simialrities (or dolphins would be grouped with seals and manatees and fish with icthyosaurs). Focusing on one character does not work and as I have *also* noted, there are plenty of differences between bat and pterosaur phalanges. Finally as I have ALSO noted already, this whole thing is basically ridiculous. Bats are not pterosaurs and there is a staggering number of reasons to note why. Please don’t fill this forum with this kind of silliness – there are other places you can do it.

  18. 30 Jack 19/03/2010 at 11:18 pm

    I learned a long time ago that when people say they have info but they are not going to give it, it is because they actually don’t have it.
    But that is okay. If you don’t have this basic info, you probably don’t have much else to contribute to my researches either. Best I find that out early and not waste time here trying to get info you don’t have.
    Perhaps your expertise is elsewhere.

    • 31 David Hone 20/03/2010 at 9:57 am

      Sorry you are either not reading what I am writing or are deliberately ignoring it. This ends this conversation. I have the information, I have spelled it out above and even listed books where more information is available (and actually you never specifically asked for any anyway). If you check my links or on my sister-site ( you can download PDFs of pterosaur anatomy for free.

      I am providing information and you are claiming that I am not, while just repeating the rhetorical question “Ah, but what about bat phalanges?” while never actually stating what these supposed similarities are. Only one of us is with holding ideas and claiming to have evidence which is not shown and it is you, not me.

      You are clearly a fool or a troll. I’ll be deleting anything else you put here along these lines. Goodbye.

  19. 32 Jack 23/03/2010 at 9:24 pm

    Goodbye Dave.

  20. 33 Jack 24/03/2010 at 5:26 am

    From David Warburton:
    To be as complete as possible (just in case there are other interested parties out there…):

    Propatagium (antebranchial membrane) is supported from the shoulder to the metacarpal of digit I. There are two phalanges, the distal one bearing a claw.

    The chiropatagium (wing membrane) is supported from the lateral side of digit I by digits II-V, DV being almost at 180 degress to DI when the wing is extended. DII-V have three phalanges each (although phalages can sometimes fuse or be lost in some bats).

    The medial apsect of DV, the side of the body and the femur and shank (tibia & fibula) support the plagiopatagium (lateral membrane).

    Finally, in those bats that are not free-tailed, the uropatagium (tail or interfemoral membrane) is attached to the tail and the inner (medial) surfaces of the femur and shank and the calcar jutting off from the ankle region (and there may or may not be a post-calcarial lobe extending caudally from the calcar).

    Bats have very limited loss or fusion of the bones in the hand compared to birds, so their phalangeal counts are the same (or very close) to our own of 14.

    • 34 David Hone 24/03/2010 at 7:25 am

      So ‘goodbye’ APART from yet another irrelevant post. This is just a list of very basic bat characteristics. You do not, as I have said now I think 4 times, actually compare it to the details of pterosaur anatomy which is what you claim. Go away.

  21. 35 Nick Gardner 24/03/2010 at 7:25 am

    this shit is so dope

  22. 36 Zach Miller 24/03/2010 at 11:02 am

    I’m actually engaged in an email conversation with this fellow on this very topic. I have gotten him to see that, in fact, pterosaurs should be ancestral to BATS, since Bats arise in the Eocene, long after pterosaurs went extinct. I also got him to see that bats and pterosaurs are very different, and cannot be a monophyletic group.

    His latest email has suggested that birds evolved from pterosaurs. Progress!

    • 37 David Hone 24/03/2010 at 12:09 pm

      Well in a sense. You have more patience than me, clearly. Obviously I don’t mind trying to help people, but equally they need to show some willing and that requires a basic level of understanding and research on their part.

  23. 38 Zach Miller 25/03/2010 at 1:01 am

    Heh. I don’t know about that. Apparently my referencing our conversation on this blog insulted him somewhat, and he has stopped all communication with me.


    • 39 David Hone 25/03/2010 at 8:45 am

      Well I don’;t think I ever like upsetting people and I always want to inspire, not put off. But equally, I give up my time to do this kind of stuff and being met with beligerence / arrogance / ignorance / aggression (delete as appropriate) by some people when a modicum or research / politeness / willingness would go a long way is not the way to encourage me to help.

  24. 40 Zach Miller 26/03/2010 at 3:41 am

    That’s really the attitude I was getting on the email thread, too. You can lead a horse to…uh…the gigantic differences between bats and pterosaurs, but you can’t make him drink the…er…diapsid skull.

    • 41 David Hone 26/03/2010 at 8:48 am

      That’s about it. People get overly focused on a couple of differences and assume the rest is unimportant or outweighed – it isn’t.

  25. 42 mattvr 26/03/2010 at 6:32 pm

    You guys are amazingly patient with, erm, some kinds of people.

    Dave, I think this really relates to much you’ve discussed before. For some reason people think Paleontology is a ‘make believe’ science where anyone with a bit of imagination can do it.

    Perhaps this is what other individuals with other kinds of degrees believe as well?

    “What I do is *hard science*, those dinosaur guys just have to dig stuff up and see if it looks like anything else.”

    • 43 David Hone 26/03/2010 at 9:23 pm

      COuld be.

      It’s certainly galling that I am asked to bestow a level of geniality and respect for an idea being thrust at me, whe, (at the risk of being provocative) the perosn is themselves showing a lack of respect for my experience and knowledge. It’s odd, demaning time and respect while failing to give it, when (one might think) it should be expected by the person who has dedicated their time to become and expert and whose time is being demaned by the visitor in question.

      You try to be polite, your try to help, you try to encourage. But it’s only human to get frustrated at times (and bloody outraged and furious on occasion). As Zach says, you can’t *make* them learn.

  26. 44 David Peters 01/04/2010 at 4:23 am

    Dave, on the subject of pteroids, why do certain workers connect the proximal propatagium to the neck when it appears that the proximal anchor should be the deltopectoral crest, as shown in your Vienna specimen at the top of this blog page?

    • 45 David Hone 01/04/2010 at 7:19 am

      I suggest you look against the specimen if that’s what you think. That’s an artefact of shrinkage of the propatagium after death (as is common in all wing membranes) and the way the specimen has been preserved. The Vienna specimen shows something very different. Taphonomy and specimen have to be taken into account.

  27. 46 David Peters 01/04/2010 at 8:12 am

    I’m a little confused by your answer. “Against the specimen”? Do you mean next to the cervical series? I assumed that was the preservation of the trapezoids, if so.

    When you have a moment, no rush, tell me how you differentiate shrinkage from relaxation. I haven’t seen any of the former in wing membranes. Plenty of the latter.

  28. 47 David Hone 01/04/2010 at 8:16 am

    No, my terrible typing. That should say ‘again at the specimen’. and should say and the ‘way the specimen has been prepared’, not ‘reserved’.

  1. 1 Neomorphs « Dave Hone's Archosaur Musings Trackback on 27/10/2010 at 9:39 am
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