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.
Evolution 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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