Revising the frog-mouthed pterosaurs: the anurognathids

If you hunt around the right bits of various websites, you can still find adverts for a book called ‘The Pterosauria’ that doesn’t exist. Conceived as a pterosaurian equivalent of the famous ‘The Dinosauria’ text book it was to have chapters devoted to each major group and some other big aspects of pterosaur biology. Originally scheduled to appear in 2009 it got put back again and again and then slowly collapsed as content failed to be produced. The ghost of it is still remains in various places where there are previews available and for many authors (including me) it was a source of colossal frustration. Months had been devoted to writing chapters that could not easily be published elsewhere as they were in specific formats and these kinds of very long and detailed species by species reviews are not accepted even by many review journals.

Thanks to Mark Witton who produced this beautiful restoration of Jeholopterus for this paper.

In my case a chapter on pterosaur origins and another on anurognathids were left languishing and a couple of attempts to resurrect them didn’t work when I ran short of time and of course they slowly became more and more out of date. However, a recent block of time appeared and I decided to dust this off and find a home for it. Much of it hadn’t dated since, well describing all the known specimens and giving a general overview of their history and anatomy was going to be the same, but there’s been an absolute flurry of anurognathid discoveries and new taxa and unnamed specimens in recent years as well as some conflicting discussions about their phylogenetic position. (You can see some of the progressions from this old blogpost I wrote in 2008 when there were only four genera known and the work that would become this paper was planned).

The anurognathids are a wonderful group of small non-pterodactyloid pterosaurs known from Europe and various parts of Asia that are perhaps the most distinctive of the early pterosaur groups and probably the latest survivors. They had bizarrely short and broad skulls made of tiny spars of bone and with few teeth and remarkably short tails for non-pterodactyloids. They were mostly small and are interpreted as having been hawking for insect prey on the wing. There are few specimens (even with the recent discoveries) that are hard to tell apart because they are all so similar and yet almost every different specimen has been named as a new species.

So they are both really unusual and not very well known and that means even if this has taken time to come to fruition, a review of them would be rather handy. And so as you might imagine, this post coincides with a new paper doing exactly that. Somewhat inevitably there’s not a huge amount to talk about here since as it’s a review, it doesn’t contain too much that’s new – the primary role is to bring things together and synthesise them so most of what is there is already known (at least to people who keep up with the pterosaur literature). Reading the review will bring you up speed if you want all the basics, but I do want to talk here about a couple of the more interesting things I have added.

The first one is the validity of the various taxa. It’s hardly unknown for pterosaur clades to be made up of lots of species each represented by only a single specimen but the anurognathids are pushing even that. While I can’t immediately think of any calls for synonymy of any taxa, the fact that so few specimens have been described in detail and the poor quality of the preservation of many means that the available lists of diagnoses have been pretty weak to date. They are not much better now, but I have at least revised and updated the diagnosis of every taxon. There are two consequences of this that are important. First off, all the current taxa seem valid, and moreover, some of the recently illustrated, but not yet named, specimens also look like they are distinct taxa and there’s probably several new names needed. Secondly, the second species of Dendrorhynchoides, D. mutodongensis is as distinct, if not more so, than many other anurognathid genera and as such needs to be elevated to the genus level.

I didn’t want to name the other putative taxa without the permission of the original describers but in this case, I named D. mutodongensis with Junchang Lu so it’s only fair game for me to sort out the naming. JC, as he was known, sadly passed away recently and he had published on multiple anuroganthid specimens so it is appropriate that in his memory I erected the new genus Luopterus to house the species. 

Next up, the variation in the different species is quite odd. Anurognathids are weirdly conservative, even compared to other pterosaur groups and while the poor preservation of the specimens hasn’t helped up find distinguishing traits between them, once you sit down and really look it’s hard to find the kinds of traits that you might normally use to separate out genera and species. That said, there are some bits of variation which while commented on before are quite notable in this context (and there is more coming on this in a future paper that I’m involved in). The length of the tail is really variable and while these are as a whole short-tailed (even the longest of them is much shorter than other non-pterodactyloids) there is really quite some difference between the longest and the shortest. I don’t know what this means but it’s an area worthy of greater attention. Similarly, the smaller anurognathids tend to have extraordinarily large heads and the larger ones rather small ones. There could be ontogentic effects here since many of the smaller specimens are juveniles but it stands in contrast with the more general isometry of other pterosaurs, and could be linked to prey sizes or even eye size. If they are, any many people suspect, nocturnal then juveniles need huge heads to house huge eyes.

The holotype of Anurognathus, the first anuroganthid

Finally, there is the issue of the ‘folded’ wings. While some disarticulation can occur in decaying pterosaurs unless the specimen has disintegrated the various bones of the wing finger stay together. Presumably they are held together by numerous strong ligaments or they would not be able to hold up the forces of flight. It’s a very derived condition since of course all other archosaurs (indeed tetrapods generally) can flex their fingers. Anurognathids however, despite having some exquisitely preserved specimens, and nearly all of them being basically articulated, show the joints of the wing finger being flexed. This suggests that they are doing something really rather different with their wings, when flying or even when on the ground. One thing to note is that this is also seen in one other set of pterosaur specimens – embryos. That implies that either anurognathids have inherited this trait from their ancestors (if they are, as some suggest, the first branching group of pterosaurs) or have secondarily acquired what is essentially a paedomorphic trait of wing flexion.

I’ll leave it there for now. There’s plenty more in the paper that you can read and there is obviously more research to come (indeed I’m working on another anurognathid paper that’s come about in part through this work) so don’t want to go over this in detail when it’s already a review. Hopefully this does sort out a few issues and pave the way for a better understanding of these most interesting of pterosaurs.

The paper is currently available online as a preprint but a final formatted version should be out soon: Hone, D.W.E. 2020. A review of the taxonomy and palaeoecology of the Anurognathidae (Reptilia, Pterosauria). Acta Geologica Sinica.