Pterosaur trabeculae

Time for another obscure word in the annals of vertebrate palaeontology and here is one that ties together birds and pterosaurs, if only in a nomenclatural sense. For those that do not know, both pterosaurs and birds have hollowed out, pneumatic bones which in life were filled with air sacs that were extensions of the lungs. However, this obviously could potentially weaken the bones and make them vulnerable to being broken and given the kinds of high forces that many of them would have to deal with (like the bones of the wing or legs for flight and landing respectively) you want to keep them strong.

IMGP2213Evolution has evolved an elegant way around the conflict here – keeping things hollow (and thus light) but strong with some biological scaffolding. The trabeculae are therefore the various small and often intricate little webs and buttresses and spars of bones that populate the insides of various bird and pterosaur bones, providing strength and support to the bone with the minimum of extra mass. These naturally tend to be denser in number and more complex in the ends of bones such as the one pictured here or those with higher stresses and strains, but they can be quite sparse in others.

Inevitably they are little discussed in the literature since in a well preserved bone you can’t see them and even in those that are broken open they are not always visible. Even if they are visible are themselves broken, or as shown here, so complex as to be beyond description. As a result they receive little attention though they are potentially very important as they may help show which bones are taking which stresses where and even in what orientation. As such there may be much functional anatomy hidden in the trabeculae and we have yet to investigate them properly, though with modern scanning methods and further interest beginning this may not be the case for too many more years.

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8 Responses to “Pterosaur trabeculae”

  1. 1 Nathan Myers 16/08/2009 at 3:09 pm

    I’m sorry to ask such a basic question, but how are trabeculae different from camellae? I.e., is it the same structure described in different terminological traditions, or are they corresponding structures in two lineages that might (or might not) have arisen independently, or are they structures that are recognizably, and maybe even functionally, different?

    • 2 David Hone 17/08/2009 at 9:34 am

      Well here you are only seeing the intricate ones at the base of a bone and elsewhere in the shaft they are essentially rods as opposed to folded layers so there is certainly more variation seen in the pterosaur bones than a typical sauropod (note: there may be rods in sauropod bones, but I have never seen them or heard of them: I’m sure one of the SV-POW guys can enlighten us). I think the nomenclatural difference is simply historical in that people were working on pterosaurs long before sauropods and in (most) cases those workers were non-overlapping and of course the two clades were considered very wide apart at the time and thus there would be no reason for them to think they might be related and share similar structures, hence the different names. (Just a hypothesis, I’ve not read enough of the very early literature to be able to establish this).

      My guess is that these are independent given the gap between pterosaurs and sauropods with non-pneumatic (or over very simple and minimal pneumaticy according to some) dinosauromorphs and basal saurischians. Still though, they are relatively close relatives and are trying to solve a similar problem so it might not be a surprise that they found a similar mechanical solution to it.

  2. 3 Mike Taylor 17/08/2009 at 3:27 am

    Shared by birds and pterosaurs, eh?

    *cough* *cough*

    • 4 David Hone 17/08/2009 at 9:26 am

      Sorry Mike you have honestly lost me there. Are you implying they are related in which case I did say it was a nomenclatural sense, or are you saying they are not called trabeculae in birds, which is how I have always known them? If the latter please enlighten me! If it is something else, what have I missed?

      • 5 Mike Taylor 17/08/2009 at 8:38 pm

        No, I am hinting that you inexplicable omitted by far the most awesome clade that has similar hollow bones reinforced by irregularly distributed bony struts!

      • 6 David Hone 17/08/2009 at 10:39 pm

        But not ones called trabeculae though. 😉 Dear me, you will cram sauropods into anything eh? Next you’ll be saying that they can fly – though Dino Frey and I did hypothesise this at one point: if you can just inflate those air-sacs with enough helium and then crank the tail as a propellor….

      • 7 Nathan Myers 17/08/2009 at 11:35 pm

        I guess you missed when we deduced that pterosaurs were just budded off sauropods’ neural spines, to carry them around when needed, and be sent off on foraging expeditions otherwise. You may think of a pterosaur as a sauropod’s over-elaborate cervical crest.

        It’s safe to say that not all sauropods had them.

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