Dave Hone's Archosaur Musings

I’m delighted that today I have a new paper out with a really exciting new pterosaur, that I think adds an awful lot to our understanding of pterosaur evolution, as well as the animal itself being rather interesting. It’s often fairly easy to say that a new find ‘fills a gap in the fossil record’ but some gaps are much bigger than others, or a situation is rather complex that can be clearly resolved with the right fine (or at least, provide an interesting new hypothesis). To follow through this new find and its implications, we need to start with a short bit of pterosaur history and evolution.

For the first couple of centuries of pterosaur research we could split them into two groups: the rhamphorhynchoids and pterodactyloids and the two simply didn’t connect. The earlier rhamphorhyncoids (now properly called ‘non-pterodactyloid pterosaurs’) had proportionally small heads and necks, a separate naris and antorbital fenestra, a short wing metacarpal, wing fingers where phalanx 1 was quite short and 4 quite long, a long fifth toe and, most obviously, a long tail that was usually bound together with long zygapophyses. The pterodactyloids were then the opposite, long heads and necks, a single merged nasoantorbital fenestra (NAOF), a long wing metacarpal, a long 1st and short 4^th wing phalanx, a reduced 5^th toe and a short and unbound tail.

This all changed with Darwinopterus and the discovery of a pterosaur with a big head and neck, an NAOF but otherwise a very much non-pterodactyloid body plan. This gave us a new grade, the monofenestratans, and when a bunch more species and specimens were found or recognised, they formed a nice cluster that were all close to one another but clearly different from their forerunners and the later pterodactyloids. It certainly answers some questions – the head and neck evolved first and then the rest of the body changed, but it’s not really showing a clear transition or pattern of all of these various characters that are being altered. All of the characters past the neck might have changed second, but in which order did they alter, and which ones came first in the head? For that, we’d really need some more intermediates, one that plugs the gap from the non-pterodactyloids to the first monofenestratans, and then again from these to the pterodactyloids? To try and simplify the problem, we have A, C and E, but can we get B and D? Well, guess what?

So in the new paper out today, I and my colleaguesdescribe and name a new monofenestratan, Skiphosoura. There’s a *lot* I could say here, but there’s a lot in the paper and a massive supplementary info section, so I’ll try and keep this short and sweet and concentrate on the big stuff.

First off, it’s huge, the biggest known from anything like a complete specimen and one of the largest things in the Solnhofen (important aside, it’s from the Solnhofen), alongside the biggest Rhamphorhynhcus and Petrodactyle coming in close to 2 m in wingspan. Although disarticulated, it’s nearly complete with almost every bone present and they are in somewhat 3D, so we get access to tons of data we’ve not had before in the monofenestratans. It has a bony head crest, it’s got big teeth, it’s pretty robust and it’s got long legs. Looking at the specimen that first time I saw it, it was clear it had some odd features and it certainly looked more derived than Darwinopterus and the others, but was it really? When we ran a phylogenetic analysis is where things really got interesting.

Skiphosoura really does come out as ‘D’ in the analogy above, it’s got a bunch of features that we associate with the early monofenestratans, but it’s also got some very pterodactyloid like features that show a transition from one state to the other and plug this gap very effectively. Even more intriguingly, Dearc, the recently described Scottish giant is pulled up from being a derived rhamphorhynchine close to Rhamphorhynchus, and to being ‘B’, the link from these to the monofenestratans. Lining these up we then get a really clear transition for pretty much all of the characters I listed up top.

The head in Dearc is notably long and its neck is longer than earlier forms, plus the naris is huge so these are all more derived that we see in the traditional ‘rhamphorhynchoids’ but are not yet at the  monofenestratan condition (and as an aside, have a more derived prepubis too, so it’s not quite all head and neck first). In Skiphosoura, we have the big head and long neck and confluent NAOF of the monofenestratans, but we also now have a longer wing metacarpal than before, the wing finger proportions are nearly all the same, so 1 is longer and 4 shorter than the earlier forms but not at the pterodactyloid ratios, the fifth toe is greatly reduced, but still has two bones and not the one of the pterodactyloids and most notably the tail is short, but still bound by zygapophyses. So, we’ve got a bunch of features that more derived than in Darwinopterus and kin, but not quite at the pterodactyloid condition.

This is really, really cool. This is giving us a real insight into the pattern and timing of changes across the whole skeleton and what that means for how and when all these different and important shifts happened. Remember that the pterodactyloids get much bigger than the earlier forms, and have a fundamental change in their wing shape (the massive reduction in the uropatagium that comes with a short tail and reduced 5^th toe) and a fundamental difference to how they walk, so these are not just anatomical traits changing, they represent a fundamental shift in their biology and with massive implications for how pterosaurs changed over time and the opening up of new niches and the creation of a new body plan. Skiphosoura and Dearc really plug those gaps and help show the transition and this should be a major source of research going forwards looking at those changes to the body plan and the implications to flight and terrestrial locomotion to explain how the pterodactyloids became the animals that they were and that dominated the Cretaceous. Hopefully this is a first, but major, step in that progression.

There are obviously various other things in this paper too, that are at least worth mentioning here briefly. While this is not the first monofenestratan from the Solnhofen, these are currently very rare and so this is quite an addition. The 3D nature of the skeleton adds a ton of new information on these intermediates and is basically the only one that is preserved like this right now, so it’s really important in that regard. We have a new phylogeny in play, that it addition to the resolution in the middle of the tree, adds some novel relationships down the bottom (or firms up some previously very uncertain areas), and on a personal level, it’s nice to see Petrodactyle included and it pop out basically where I thought it would, and with some more characters supporting it’s identification as a valid taxon. I should mention at this point, that there’s a ton of new characters in this tree (which is really comprehensive) and, if we’re right about the relationships, there is a serious bit of taxonomic revision needed on the various Darwinopterus-like taxa with animals previously considered different species of a single genus being spread around the tree. Finally, we have some commentary on ecology and behaivour of these animals, so there is a lot crammed in and stuff that is relevant to pterosaur evolution, taxonomy, relationships, anatomy, flight, ecology and more. It is, therefore, I think fair to shout about it quite a bit!

Obviously to round off, I want to thank my collaborators and coauthors, Adam Fitch, Stefan Selzer, and René Lauer and Bruce Lauer (and the Lauer Foundation). It’s taken a ton of work to get to this point and I’m delighted we made it. Now go read the rest of the paper because there’s a lot to unpack here and this isn’t doing much more than scratching the surface. You can access it here:

Hone, D.W.E., Fitch, A., Selzer, S., Lauer, R., & Lauer, B. 2024. A new and large darwinopteran reveals the evolutionary transition to the pterodactyloid pterosaurs. Current Biology.

While I’m posting links, it seems like a good opportunity to mention that like so many others, I have made the leap to Bluesky, and I do also have a (not that much used) LinkedIn account too. So if you want to follow me there, please do. For now my Twitter is still running, but I think it’s only a matter of time till that fades, but my Facebook page is still doing fine. There will be a new episode of Terrible Lizards next week that will be all about this paper, so more info coming there soon too.