The DinoBase Public Forum

There are a few fundamental biases in the fossil record and they can heavily influence what you are looking for. The older something is, the less likely you are to find it – every million years older it gets is another million years for it to be subducted, buried, eroded or destroyed. The smaller something is, the harder it is to find – 50 metre sauropods leave behind big bones that can be seen on the surface from half a mile away, rodent teeth are another matter. The more delicate something is, the rarer it is – it is more vulnerable to destruction before and after fossilisation, and even if you find it, it might be so badly crushed that all the details are lost. Finally, the rarer something was in life, the less likely you are to find it – a species with billions of individuals is more likely to enter the fossil record than one with a few hundred.

It might come as little surprise then to learn that despite intensive searches, and some very productive areas having been swept, Triassic pterosaurs are exceptionally rare. They are small, fragile, old and probably very rare (the group had jus appeared). Most of the few we have are badly crushed and have much of the animal missing.

However, (and this is a damned big ‘however’, with hobnailed boots on, and a large neon sign with ‘HOWEVER’ written on it round it’s neck), that has just changed. Raeticodactylus filisurensis is almost certainly the best preserved, most complete and generally all round excellent Triassic pterosaur known. It is in wonderful condition and tells us an enormous amount about the early days of pterosaurs. To pile glory upon glory, it is also totally bizarre and contains a number of very unusual features that make it unique in a great many ways. It would be going far too far to say it will revolutionise our understanding of the early days of pterosaurs, but it will add a massive chapter to what is currently a very short book.

That we have Raeticodactylus at all is a testament to it’s ‘father’ Rico Stecher. I have a whole blog post planned on Rico and his work, but in short he is simply a keen palaeo amateur who fond the specimen, prepared it, described it, presented his findings at a meeting (for which he had to take time off work to attend!) and then got it published. It is a fantastic achievement and one which I will write about extensively in due course. Rico will get his plaudits, but first I want to talk about the pterosaur. I met Rico while he was working on the description, he had come to Munich to look at our Triassic pterosaur material and we discussed his specimen at length, and ultimately I acted as the ‘translator’ on the description, giving the English a polish and helping him with some of the more technical aspects of the description. As a result, although I have not seen the specimen, I do know it pretty well having gone over the description several times and discussed it with Rico at length and have seen numerous photographs. As such I hope I can give some interesting insights into this bizarre little critter.

First off, as ever, I have no photos here, sorry. However there are some at Laelaps (I got beaten to the punch as Rico asked me to wait with this post until the paper was published, but Brian found it online early!) and even two seconds should be enough to convince anyone with a passing acquaintance of pterosaurs to realise how odd this guy is. Rico came to the Wellnhofer meeting in Munich and had the penultimate talk of the conference (immediately before Peter himself). I must confess to a little showmanship on my part as I was the only one who knew what was coming when he put up his first slide. I turned in my seat and quite literally saw jaws drop – yes, it is *that* weird.

Raeticodactylus is a rhamphorhyncoid pterosaur (obvious from the age and the skull shape) that can be diagnosed by any of about a dozen autapomorphies. I will not dwell on lots of interesting sublties – anyone *that* interested can go and read the paper, but there are still a large handful of very, very interesting features about Raeticodactylus that are worth discussing.

The most immediately striking thing about the specimen is the skull. Pterosaurs are well known for sporting some bizarre headgear, but even so this is extreme – especially in what must be a very basal taxon. Bony crests appeared *very* early in pterosaur evolution. The lower jaw is almost as strange, it has a deep anterior ‘keel’, the whole thing is very robust, the dentary is about half the size one might expect of a pterosaur and the articular is simply colossal (though quite possibly tied to the fact that the jaw is so damned big in the first place – it will need a big lever to shift it!).

The teeth are also interesting. Heterodont dentition is not that rare in pterosaurs (think Dimorphodon!) but there are unusual regardless. They show some nice fangs at the front and behind some nicely cusped teeth. Now previously cusps have only been seen in eudimorphodontids in pterosaurs, but several features suggest that this is *not* an eudimorphodontid. In short, cusped teeth evolved twice, and furthermore, there are a bunch of Triassic pterosaur fragments assigned to Eudimorphodon purely on the basis of cusped teeth – we might need to look at these again! Even this is not quite the end, and the teeth in the upper and lower jaws are arranged differently – tightly packed and overlapping in the mandible, but well spaced in the upper jaw. It gets harder with each passing sentence not to add an exclamation mark to the end of each line here, this thing is nuts.

The humerus is interesting as it is extremely long and slender. This does not make sense. If the damn thing was trying to fly it wants a short and robust humerus. Short to reduce the cycle time of a wingbeat, robust to support the heavy and powerful flight muscles required for powered flight (especially in such a basal taxon that one has to assume is not a great flier compared to some of the later clades). What was it doing? It certainly has the classic complex humeral head of a pterosaur indicating that there were extensive flight muscles, it is certainly not a glider or anything like that, but it is strange.

The femur is however, to those in the know, perhaps the crowing glory / weirdness of Raetico. Basically it looks like that of a theropod, or for that matter any of the derived archosaurs / ornithodirans that pterosaurs are derived from (in all probability – see number 15). It is long, slender, shows a nice sinusoidal shape and comes with a proper 90 degree angled head with a distinct caput. One of the ongoing issues over pterosaur origins is the relative lack of characters to tie them to possible ancestor clades and while the balance of power is with an ornithodiran origin, the evidence is still scant. This is therefore an enormous piece of the puzzle, which certainly *implies* a very close tie between Raetico (and by extension other pterosaurs) to the ornithodians.

Clearly there is still much to do. The paper out now is ‘simply’ an involved description and diagnosis and at the very least it’s systematic relationship to other pterosaurs needs to be determined, and further to that the possible implications for pterosaur origins. Other work is in preparation already on this taxon and Rico has kindly invited me to be involved with this work, so there is more to come. On the face of it, it does have characters that tie it to several other basal pterosaur clades and yet it is still very unusual. Rather like the anurognathids, it has some *very* basal features which are apparently combined with some highly derived features, and thus it could be a very basal taxon that is simply highly modified.

I am speculating (with an experienced eye) but I suspect it might just be deserving of its own family. It certainly has more autapomorphies than pretty much any other pterosaur I can think of off-hand given that it is perhaps only 50% complete. It’s systematic position is likely to be complex too because of the combination of features – it *could* just, possibly, turn out to be the most basal pterosaur known. It could also nest with the scaphognathines, or even collapse the rhamphorhyncoid tree to a bush. In short there is much to do here, and while it will be quite sometime before something is published on it’s systematic and phylogenetic affinities I suspect that pterosaur researchers are already plugging it into their matrices to see what happens.

For now though, the conclusions are simple. We have a great new specimen of a Triassic pterosaur that is well preserved, fairly complete and shows off a hatful of unusual features, both basal and derived. So, welcome Raeticodactylus to the literature, there are many people waiting to see what secrets you can reveal.




Edit: Without my knowledge, I have discovered that this post has been cross-posted to another site. For any visitors coming from there, please do explore the rest of the site. If nothign else, I have written two more pieces on Raeticodactylus!

Last edited by David Hone (2008-04-22 09:30:51)