What on Earth are pycnofibers?



You 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.

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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