What on Earth are pycnofibers?

Viewing6You wait month to publish a paper and then two come along in as many days. So with the baby killing theropods now dealt with, we can turn to pycnofibers.

Yes, finally that term all pterosaur workers have been waiting for has been established. Pterosaur ‘hair’, ‘body fibers’, ‘fur’ and the rest can be consigned to the bin to be replaced by the term pycnofiber. A new paper in Proceedings of the Royal Society B led by Alex Kellner (pictured), however redescribes some of the soft tissues from the wonderfully preserved anurognathid pterosaur Jeholopterus from the Yixian and sets this problem to rights by coining the term pycnofiber. It really is more of a housekeeping issue than anything else, but a useful one. Of course that’s hardly the main thrust of the paper in which we discuss the structure of the main wing as well as the pycnofibers themselves with both new observations and some more UV work from Helmut Tischlinger.

For those not keeping up, pterosaurs (among a great deal of other known soft tissues) were basically furry. Some at least (and given the sparsity of their preservation quite possibly many, or even all) were covered in some kind of integumentary fiber that looked really quite like fur. The best known of these is Sordes pilosus (the ‘hairy devil’) which is often mentioned round about this point as the best, but not only, example.

However being, well, pterosaurs one could hardly call their ‘fur’ fur, or hair for that matter, these being the preserve of synapsids (and by extensions, mammals). Nor (despite some calls for it) could they be considered protofeathers as there is no established homology between them and saurischian protofeathers and feathers (or for that matter ornithischian dermal structures). This has left pterosaur researchers with a problem – these are clearly different things and we refer to the quite often but with no-one having gone out onto a limb and named them, we were left with a variety of half-names all of them convoluted or presented in quotation marks.

This has been an issue for a while and I actually ended up discussing the idea of having a formal name (or at least acronym) for them to try and clear up the confusion with Daves Unwin and Martill not too long ago. (Ultimately they rejected my Pterosaurian Integumanraty Structures as forming the inappropriate acronym PISs, though I felt this a. wasn’t the point, and b. was quite pleased with my purile effort, though the ideas to have *something* persisted). Fortunately however this search is now over and the pycnofiber is born.

The counterplate of Jeholopterus. Modified from Kellner et al. 2009.

The counterplate of Jeholopterus. Modified from Kellner et al. 2009.

We of course also talk about other things in this paper, first off confirming that in this specimen the wing membrane attaches at the ankle and also that despite the short tail, there is a broad uropatagium (the rear wing) present. For the first time we observe actinofibrils (those fibers that support the wings) lying in multiple layers (not just a single one) and these tend to cross each other a little, though they are essentially subparallel. This tells us something about the structure and to a lesser extent function of the wing.

I won’t go in to this in more detail, not for lack of interest but simply because it rapidly gets very technical after this and requires quite a mountain of background knowledge of pterosaur anatomy and several decades worth of debate about various minor issues some of which are at least clarified here. I also have more things I want to say based on this work that will be going into another paper or two that I’m working on so understandably I don’t want to splash it around the web while I’m still writing it, so sorry if this report is a bit underwhelming. If you are really desperate to read into all this you can of course just read the paper since that’s kinda the point of publishing them.

Alexander W. A. Kellner,, Xiaolin Wang,, Helmut Tischlinger,, Diogenes de Almeida Campos,, David W. E. Hone,, & Xi Meng (2009). The soft tissue of Jeholopterus (Pterosauria, Anurognathidae, Batrachognathinae) and the structure of the pterosaur wing membrane Proc. R. Soc. B : 10.1098/rspb.2009.0846

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24 Responses to “What on Earth are pycnofibers?”

  1. 1 Thomas R. Holtz, Jr. 05/08/2009 at 8:30 pm

    Very cool. Congrats to you and the rest of the team.

    Also, I note that Alex is so tall he has to bend over to fit into a photograph…

    (And all this reminds me: still need to order that Pterosaur volume!!)

  2. 2 David Hone 05/08/2009 at 9:40 pm

    Hi Tom, thanks very much for the kind words and yes, DO order a Wellnhofer volume!

  3. 3 David Marjanović 05/08/2009 at 10:31 pm

    Nor (despite some calls for it) could they be considered protofeathers as there is no established homology between them and saurischian protofeathers and feathers (or for that matter ornithischian dermal structures).

    Does the paper demonstrate nonhomology, though?

    • 4 David Hone 05/08/2009 at 10:40 pm

      No but I think the burden of proof should be to provide homology than prove non-homology. Given the uncertain phylogenetic position of pterosaurs and (even if they are ornithodires) the gap between them (phylogenetically and temporally) and protofeathered dinosaurs, I think it’s safer to assume they are not homologous at this point.

  4. 5 Zach Miller 06/08/2009 at 12:39 am

    Bah–I keep forgetting about that pterosaur volume, too!

    Sounds like a great paper, but your link at the end of the post is busted, and a look at the “current issue” of Proc. Roy. Soc. B reveals no pterosaur paper… :-(

  5. 8 Tim Morris 06/08/2009 at 11:18 am

    Somehow, greg paul’s outdated musings about “dinosaurs not extinct if there were mouse sized forms” sound like a load of hooey.

  6. 9 mythusmage 06/08/2009 at 1:41 pm

    You do realize people are going to call it hair and fur anyway. There are popular terms and there are correct terms, and they’re not always the same. :)

  7. 11 Taissa 06/08/2009 at 3:55 pm

    I am still laughing with the name PIS. =D

  8. 13 Christopher Collinson 07/08/2009 at 10:14 am

    Dave, after reading the paper I have couple of questions. First when you say that the tenopatagium was “extensively covered
    by elongated and thick fibres here called pycnofibres.” Are you meaning to say that the pycnofibres were originating from the membrane or that the pellage of the body was just sort of sticking out laterally and overlying the proximal portion of the membrane? Secondly, could you provide more insight into the individual structure of the pycnofibres? They are said to be “further formed by smaller fibrils.” But how exactly are the smaller fibrils arranged, and why is it clear that is so?


    • 14 David Hone 07/08/2009 at 10:47 am

      Hi Christopher, thanks for your questions but I am sorry to say that I can’t really answer them since I have not examined the specimen in sufficient detail to really say so and i don’t want to put words into Alex’s mouth by speaking about how he interprets the material. I’ll see if I can get him on here to post an answer for you.

  9. 15 Dave Unwin 07/08/2009 at 5:43 pm


    I’ve been through the Jeholopterus soft tissue paper and found it very confusing.

    Just to get the ball rolling, here are a couple of lines from page 6, para 1:

    This is a very interesting claim that has important implications for the origin and homology of pterosaur ‘hair’ although, so far as I can tell, these implications are not discussed in the paper. More importantly, there does not appear to be any visible evidence for this ‘composite’ morphology in the illustrations and no further details are given in the paper. So, what exactly is the basis for this claim?

    How is this possible? Elsewhere in the paper you cast doubt on any homology with protofeathers.

    • 16 David Hone 07/08/2009 at 10:47 pm

      It may sound like a cop-out but this isn’t – Dave you know well that by definition not every author writes every bit of every paper or necessarily agrees with everything in it. As such, you really need to speak to Alex about this, not me.

      I would say though that we were well over the page limit for a Proc R Soc B paper and had to cut things out as well as pay the extra page charges. It’s not easy to cram in that much of a redescription and then cover all the implications of wing structure, preservation, claws, actinofibrils, pycnofibers etc.

      In any case I think the points you raise here are not mutually exclusive: we can hardly examine the homology (or otherwise) of various strucutres without a good understanding of their evolution and structure. As such, the identification of the composition of pycnofibers can hardly not have important implications for working out the homologies – just becuase they share soem features does not make them necessarily homolgous (depending on your level of homology of course – at one very deep level hairs are likely to be homologous with feathers). In short I don’t see the contradiction between pycnofibers having a similar composition to feathers and not actually being homologous with feathers.

  10. 17 Monad 03/11/2010 at 3:10 pm

    Hi Dave – I was reading the Jeholopterus paper you authored with Kellner and several others and it states with regards to pycnofibres that “They were possibly mostly composed of
    keratin-like scales, feathers and mammalian hair.” This seems to have confused some people:


    but I’m guessing just a typo – hyphen in the wrong place?

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