Pterosaurs – such beautiful fossils, but so much controversy

I think pterosaurs are cool and unusual for all sorts of reasons. However, one of the unique things about them is the controversy they attract. I have seen more in depth discussions (and vociferous arguments) based on pterosaurs than anything else in the palaeo community and I have a hunch as to the answer.

Pterosaur fossils are really very unusual compared to say dinosaurs or corocdiles. We have quite a few specimens (in the thousands, for relatively complete bones in tens of thousands for fragaments and isolted elements – though the majority represent just three genera – Pterodactylus, Rhamphorhynchus and Pteranodon) and a decent amount of diversity a hundred or so genera). But here things start to break down – while many pterosaur specimens are truly beautiful and amazingly preserved (for small fragile little things) they are also incredibly ambiguous.

Crushed flat and only preserved from a single orientation, pterosaurs do not provide half the information you might expect from a dinosaur fossil in a similar condition. The ends of bones (and thus the joints) are often not exposed, or are covered by calcite crystals, skull bones are fused together so well that we cannot trace their outline to see how they fit tighter and what this might mean for their origins and relationships, the flight membranes (if preserved) are usually detached and loose so their actual shape and orientation is hard to reconstruct, they are so shorn of normal cladistic characters the systematics of even some well know groups is highly uncertain and plenty more besides.

In short, even two great experts with years of experience, having seen the vast majority of known specimens and with an intricate knowledge of reptilian anatomy can come to very different conclusions about a given specimen. It happens with pterosaurs. A lot.

Can the leg rotate like this because the joint is loose, or is this a function of a lightweight skeleton and the joint would have been severely restricted in life? How do you tell who is right? How can we ever tell? Take the first and the animals could perform amazing feats of flight with amazingly disjointed limbs, take the second and they are far more normal reptiles that are the victims of capricious fossilisation that do not give us the whole picture.

Such is the fate of pterosaur research, but it is a situation I just do not see with the dinosaurs except perhaps when it comes to the birds. There we have the same situation – glorious specimens with feathers and other soft tissues regularly preserved, but with just the right amount of ambiguity in both that getting an exact reconstruction that everyone agrees on is all but impossible.

With a good 3-D skeleton you have a good idea about many aspects of the joints, orientations and how muscle scare might have influenced muscle shape and locomtion etc., prominent teeth and an understanding of how the skull bones operate as a unit give a good indication of feeding and lifestyle, and the detailed structure of vertebrae etc. can reveal secrets of support and locomotion – all of which in pterosaurs are either lost, highly reduced or cannot be determined. With a good dinosaur skeleton people might disagree on the details, or interpret something like the feeding ecology differently – but the basics will be agreed on by everyone – either the evidence is clear-cut, or simply not enough information is available to make a decision and even then it tends to be pretty minor. For all the hoo-ha that surrounds T. rex and the use of its fingers or how fast it could run no-one argues that it was a quadrupedal herbivore that lived in shallow water, yet these are the kinds of questions that are still not finally settled for many pterosaurs.

Still, disagreement might be rife (and even occasionally bitter) but it makes work more interesting and more rewarding. If you think you are onto something new, you have to get it right and convince all the doubters using every bit of evidence you can muster and determine every other possible interpretation of the data and how it might affect your ideas. If nothing else you can look forward to a long series of papers attempting to rebut the ideas of your colleague whose thoughts contradict your own while he does that same to you. Just occasionally though I would like a more definitive answer on some aspect of pterosaurs – it is very rare that someone comes up with something and the only response to be ‘yes!’

This is a revised version of a Mk.1 post, to see the original with comments etc. go here.

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