*Edit: big picture finally fixed!*
With my choice of blog header (thanks again Luis!) I thought it about time I covered (albeit superficially) the fascinating world of pterosaur head crests. For all the (justified) interest that dinosaurs like Parasaurolophus and Styracosaurus provoke, really they can’t even begin to touch some of the more extreme pterosaurs in terms of diversity and, when you consider these things actually fly, size.
The header is an extract from a larger image of some of the biggest and most bizarre crests going and I have put up a copy of the original here to show off both Luis Rey’s artwork and the pterosaurs in all their bizarre glory. Shown are (L-R): Tropegnathus (by a nose), Dsungaripterus (curvy), Tupuxuara, then Tapejara imperator top – (soon to be renamed), Caulkicephalus (middle – orangey) and finally Nyctosaurus (actually seen with a reduced posterior bar – most unlike Luis to miss out on the opportunity to make something bigger!). These are all derived pterodactyloids, but actually crests extend across the whole of Pterosauria and there is barely a clade that does not have a crest of some form or another.
Actually, most branches of the pterosaur tree have at least one crested taxon, and indeed crests are so prevalent, it is quicker to list the clades which definitively do not have any crested members, and this is limited to just the basal dimorphodontids and anuroganthids. . It is actually pretty safe to infer that many pterosaur species for which crests *aren’t* known probably also had one of some description, given just how many had them, and because many species for which there is no evidence of a crest may have had a hidden one (see below). What is also interesting is the fact that many crests must have evolved independently many times over given the differences seen in crest morphology, in different parts of the pterosaur tree, and the different bones involved in their construction.
There are a variety of bones involved in crest construction in pterosaurs (though the fused and suture-less nature of adult skulls can make identifying them very difficult). At the very least though we see crests derived from the anterior part of the skull (and often including the lower jaw) in the ornithocheirids, many that rise vertically off the top of the skull like in Raeticodactylus or Germanodactylus, those that cover the top and rear of the skull like Thalassodromeus and those that project backwards such as Pteranodon or combinations of them such as in Dsungaripterus. There is more variety than this to be sure, but these extremes cover the range of morphologies (though often somewhat smaller than the ones described here – just look at the nubbin of a crest on Quetzalcoatlus).
Next we need to consider their actual composition – what are the crests made of? Bone is the obvious answer, but in many, if not most, pterosaurs it is not the full story as we shall see. Bony crests are of course relatively easy to find, if you have the skull of a pterosaur preserved from a crested species, chances are a crest will be preserved too, if only in part (they tend to be thin and thus break). However, even this is no guarantee – Nyctosaurus was long thought to be effectively crestless with perhaps simply a small bump at the back of the head, as the various skulls know for the animal tended to have the rear part broken off. Of course a pair of dramatic new specimens (see Chris Bennett’s site here for more) showed that not only was Nyctosaurus the owner of a crest, but if far outshone pretty much every other pterosaur going.
Importantly, there is also a soft tissue component to be considered too. The most dramatic examples are the magnificent tapejarids and especially imperator with an enormous extension of tissues springing from the back of an apparently thin and short bony crest at the front of the skull. There are two distinctly different soft tissues present in Tapejara imperator, with the lower part clearly having some form of stiffening fibres, and the upper one without. One also sees on a number of pterosaurs (including Germanodactylus) striations on the bone for the soft-tissue to attach to, giving it a firm anchor point on the skull. In Tapejara (pictured) especially we see a kind of grading of the bone working into the soft tissue as one transforms into the other.
Furthermore, there may be a number of ‘untapped’ crests yet to be found, and as hinted at above these might be present as soft-tissue crests even if forms with *no* bony crests. Perhaps inevitably, it is the UV work of Helmut Tischlinger that has revealed this as can bee seen with the presence of soft-tissue crests found in Pterorhynchus (where there is no bony component), Pterodactylus (a small occipital cone, but probably a fuller anterior crest too) and Germanodactylus (which has a simple and small bony crest). So those taxa for which there is only a slight pony protuberance, or even no apparent crest at all might well have had significant soft-tissue crests. Despite the extensive range of taxa which we already know were crested, it is possible that may others were too.
I’m not going to comment on crest function here if only because I want to talk about more fully once a couple of my own papers on the subject make it into print (the first is out in a couple of months) thought plenty is available elsewhere online (much of which I disagree with, which is another reason I am waiting for peer review to grind its way to publication). However, there are a couple of general comments worth making about crests in general before I finish. First of all is that while there is either direct or good supporting evidence for soft tissue components for some crests (like in Dsungaripterus) there is none at all for others (notably Pteranodon and more recently Nyctosaurus). Secondly, with the notable exception of Pteranodon, there is no convincing evidence (well, no studies!) that demonstrate sexual dimorphism in pterosaur crests and thus where we have lots of crested adults (like Sinopterus) this includes both males and females with crests). Finally, while I disagree with much that has been written about crests (both inside and outside the scientific literature) on thing that is rarely taken into account is the sheer diversity of crests out there – too often you see a reasonable account and analysis of the possible function of say the crest of Pteranodon and then this is applied ‘flat’ to ‘crested pterosaurs’. Come on, you just *cannot* compare Pteranodon to Tapejara, Tropegnathus, Dsungaripterus and Tupuxuara. They have different sizes, shapes, weights, distributions and compositions. Any explanation of crest function must take into account this variation, or limit its scope to one clade or crest type.
I’ll leave crests there for now, but this is a subject I’ll return to soon (-ish), so stay tuned.