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of attempts to resurrect them didn’t work when I ran short of time and of course they slowly became more and more out of date.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.

Terrible Lizards, series 2

A few months ago I put up a post to launch a dinosaur-centric podcast called Terrible Lizards. I and my co-presenter, Iszi lawrence, really didn’t know how popular it might be or how much momentum it would get. As such we recorded one series and then crossed our fingers.

Happily, it has been well-received and encouraged we have recorded and are already releasing episodes for the second series. The first couple of episodes are already up and we’ve kicked off with two taxa that feature regularly in the Musings in Velociraptor and Protoceratops.

All of the episodes of both series 1 and 2 are available here. It’s also available on iTunes, Spotify and all kinds of other platforms so it should be easy enough to get hold of it on your favourite website or set-up. New episodes will be coming every Wednesday for the next few weeks and there’s extra stuff available for some of our patreons too.

 

A second specimen of Luchibang?

I was going though a bunch of files this week hunting down some photos of Chinese pterosaurs and came across this one. I took it in a small private museum in Liaoning ten years ago and so didn’t record any details at the time since the material was never likely to be accessible for study and I was only there for an hour or so. There’s also no scale and of course the lighting is less than ideal. My memory of it is sketchy at best, but I remember it being quite a large specimen, though if it has stuck in my mind any further it would have been obvious then (and indeed more recently) what it looked like – it could be a second specimen of Luchibang.

A second specimen of Luchibang?

One thing that was very difficult with naming that taxon was establishing that it was genuine given its unusual mixture of features and proportions. Despite a very extensive section in the supplementary information of the paper on nature of the specimen and extra preparation work to establish that is is genuine, I’ve still seen comments online (including from people who should know better) claiming it might be a composite. I have though also heard of other specimens in China that are long-legged istiodactylids and apparently I’d already seen one but forgotten.

This is clearly an istiodactylid based on the skull, with the classic rounded jaw tip and teeth limited to only the front of the mouth. Like Luchibang and indeed a number of Liaoning istiodactylids, the mandible has rotated and is not in lateral view like the rest of the skull (though here the skull is rather crushed). The neck vertebrae are similarly ornithocheiroid-like and also preserved in dorsal view. The wings and legs though are not like ornithocheiroids, with a wing-finger with distinctly azhdarchoid-like proportions and long hindlimbs with large feet. This would generally be an odd combination, but taking some quick measurements on the photo shows that the broad proportions of the jaw, coracoid, humerus, ulna, wing metacarpal, wing phalanges, femur, tibia and metatarsal are all very similar to those of Luchibang. At the bare minimum that makes this extremely intriguing and without looking further into it, does make this a potential second specimen.

That said, there needs to be caution here. Looking as closely as possible at this less than perfect photo, throws up some oddities. The toes are a rather odd colour compared to the rest of the skeleton (though they look like they might simply not have had lacquer put on them), the humeri look weirdly wide (though could be crushed), and the wrist elements appear to be missing. There’s some kind of odd effect around many of the bones which could be clean up work and some filler, but could also be where bones have been moved around to make things look better, or of course rather worse, have been added in from another specimen. Even so, as with Luchibang, there is very considerable overlap across numerous elements. The mandible overlaps one of the wings, the cervicals overlap with the scapulocoracoid, the proximal wings and femora overlaps with the mass of bones of the torso and other wing and leg parts are in close association with each other.

So while I’d preach caution about this specimen without much better photos (and of course far better still, seeing it in person), it is a credible candidate for a second long-legged istiodactylid. Despite the fact that it looks like it has had work done on it, it would be rather odd indeed that someone had created a composite where they had managed to find an istiodactylid skull with a first wing phalanx of the correct length underneath it and of the right colour and preservation type to match with an unrelated azhdarchid body of the right size and proportions, that happens to have an ornithocheird-like posterior cervicals on it, and where all the different elements are a match in size for a second, unrelated specimen. In short, while some details are a little questionable, it looks like the majority of the elements as presented are all from a single specimen and that’s an azhdarchoid-like winged and legged istiodactylid, and right now that means Luchibang.

More and better presented specimens with proper descriptions are really needed here, but I think on balance this provides reasonable mutual support of both specimens being genuine. The faked Chinese fossils I’ve seen have numerous obvious anatomical issues or the composite parts are of very different preservational quality and type. Even poorly faked and restored specimens are often sold for very large sums and the goal is to produce something extremely aesthetically pleasing, not scientifically plausible, so there’s little motivation to make exceptional and high-quality fakes, especially from specimens like this one where the skull is mashed up. As such, then as reported, there do appear to be more of these istiodactylids out there with the potential to explain a lot more about their unique proportions and ecology and this is hopefully only an indication of more to come from Chinese collections.

 

How to grow your dragon – pterosaur ontogeny

Life reconstructions of Rhamphorhynchus on display in Munich.

The giant pelagic pterosaur Pteranodon is probably the most famous, and is certainly the most iconic, of pterosaurs and specimens and casts of this show up in museums around the world. There’s something like 1100 specimens in public collection and plenty more in private hands. Unfortunately though, almost all of them a squashed very flat and they are often rather distorted and worse, the overwhelming majority are very incomplete and often composed of only a few elements. They are also almost all of a good size (‘subadult’ and up) with only one specimen recognised as being something close to juvenile in age. That means that while this is an amazing number of specimens, it’s also really quite hard to work with as the data is limited in lots of ways.

However, if we turn to Rhamphorhynchus we have only a fraction of the number of specimens but pretty much all the other issues are absent. Most specimens are complete or at least have a very healthy amount of the specimen present, they are often flat but show nothing like the distortion of Pteranodon and there are even fully 3D specimens. They also cover a near order of magnitude in size with everything for animals of c 30 cm wingspan up to nearly 2 metres and include everything from putative hatchling-sized animals to a couple of genuine outliers that are much bigger than other known individuals. Thus despite the relatively low numbers they represent and absolutely fantastic resource for studying various aspects of pterosaur biology.

The numbers of course are not tiny, well over 100 good specimens, and that alone would make them an exceptional sample of most terrestrial Mesozoic archosaurs. The legendary Solnhofen researcher Peter Wellnhofer catalogued over 100 of these in his amazing 1975 monograph on them and this dataset has become an industry standard for pterosaur research ever since. However, we are still discovering more and there are plenty sitting in various collections around the world that nave never entered the literature because, well, there’s already 100 of them out there. But even big samples are improved with the addition of more material and so for the last decade I’ve been scouring collections and databases and hunting down every specimen I can to add it to Peter’s data. That takes us from his total of 108 to 129. The ‘real’ total is actually a little lower since several of his were in private hands and two of mine are casts, though of unique specimens, and not all of these are complete. Even so, it represents a hefty increase in the available data and marks the first major increase in the catalogue in 45 years.

Obviously I’m not going to make a dataset like that and sit on it, so this post inevitably marks the publication of an analysis of growth in Rhamphorhyunchus. In a lot of ways, this mirrors Chris Bennett’s fantastic 1995 paper on this genus where he convincingly demonstrated that all specimens belonged to a single species and not multiple ones as previously thought, and part of his arguments for doing this looked at the relationships between various elements based on Wellhofer’s dataset. Chris’ point was that while there were some discreet clusters of specimens (which he attributed to year classes) most of the alleged differences between the putative species vanished when you put them on a graph and the rest were classic ontogenetic traits like the fusion of the pelvis in large individuals of big eyes in small ones. So while he didn’t really deal with growth as such, he was already showing similar patterns to what I and my coauthors confirm now – Rhamphorhynchus was weirdly isometric in growth.

In other words, in the case of the vast majority of their anatomy, young animals are basically just scaled down adults. This is a weird proposition for a terrestrial vertebrate as most undergo some quite notable and even extreme allometry with some parts proportionally growing and others shrinking as they grow. Think of young animals with big eyes, in big heads and large hands and feet, or antelope with especially spindly legs and so on. But in the pterosaurs even the smallest animals are, aside from the eyes, basically carbon copies of the adults.

Rhamphorhynchus

One of the less well preserved Rhamphorhynchus out there, it nevertheless has most elements intact

To put this in context we looked at another group of quadrupedal, powered flying vertebrates with bony spars supporting membraneous wings, the bats. Yes, obviously they are not ideal in terms of their ancestry but functionally they are about the best analogue you could get for a pterosaur. Looking at their development we see that juveniles have proportionally very small wings and right around the time they start to fly and become independent, their wings grow rapidly. This is the pattern we would expect, young animals have only so much they can invest in their development and growing wings that are not being used is what we would expect, exactly as things like sheep (and indeed dinosaurs) don’t grow their horns until they reach sexual maturity, they are not being used before then. We do though, see the bats developing their legs early as they need to grip into cave roofs and their mothers so it’s not a case of overall reduced development of limbs, but clearly selective growth.

Birds are functionally poor analogues of pterosaurs but are much closer phylogenetically and are the only other powered flying tetrapod so we also looked at some existing datasets for them too. Most birds, unsurprisingly have allometric growth of various elements, but like bats the legs develop before the wings with one notable exception, those that are hyperprecocial. Some birds like mallee fowl are capable of flying within days, or even hours of having hatched from the egg. These birds have isometric growth and this immediately then suggests that Rhamphorhynchus at least (as has been suggested before) was precocial and flying while young.

This may sound correct since if you are flying when young and flying when adult you probably want to be the same but that’s not the case. As a flying animal in particular, relying on wings to hold you up you have a problem. If you grow isometrically you wings will get longer and wider but your weight will increase much faster since you as a whole will get longer and wider and deeper. So mass will increase much faster than wing area and that can only have a profound impact on how you fly. There are two things that might offset this, first of all different animals can use different flying gaits at different sizes which might mean that performance is not quite as different as might be predicted from this (though we’d still expect juveniles to be more agile) and secondly, changes in pneumaticity. Birds increase penumaticity as they grow and there’s evidence this is the case in other pneumatic clades too and if so for pterosaurs, then the mass increase in adults would also be offset somewhat by a proportionally lower mass in adults for a given volume than juveniles.

Precociousness has been suggested in pterosaurs before based on the evidence for them flying while young, but it has also been challenged. It suggested that to be flying at that size would require a huge amount of effort and this would leave little energy for growth. That’s largely true, but overlooks that there could be post hatching parental parental care. That is normal for archosaurs (including dinosaurs) and we would expect it for pterosaurs. Being precocial in terms of the ability to move does not mean they have to be independent, things like horses have babies that are capable of running within hours of birth but are still suckled for months, and various ducks take their ducklings out to sea soon after hatching. That’s obviously not the quite same thing as the energetics of flight, but it does show that being a good locomotor is not mutually exclusive with parents protecting and feeding their offspring.

So in short, Rhamphorhynchus is perhaps the best pterosaur for large studies about populations and growth and this genius at least grew isometrically, and this may or may not be the same for other pterosaurs. This then may or may not have some big implications for pterosaur taxonomy which is often based on the ratios of various wing elements. But it does imply that young pterosaur could fly, and fly well and that adults and juveniles were probably flying in different ways to each other and that could then have implications for where and how they foraged and what they ate. This is an incremental step in our understanding of this group (and again, much of what we say has been said before but this firms things up nicely) and hopefully opens up the options for further research on them as living animals.

 

The paper is open access and available here:

Hone, D.W.E., Ratcliffe, J.M., Riskin, D.K., Hermanson, J.W. & Reisz, R.R. 2020. Unique near isometric ontogeny in the pterosaur Rhamphorhynchus suggests hatchlings could fly. Lethaia.

Terrible Lizards – a new dinosaur podcast

With a near global lockdown and people stuck at home there’s been a rash of new podcasts forming (or at least a rash of jokes about everyone starting new podcasts while they are stuck at home) and here is the latest (and by extension, greatest) – Terrible Lizards. In my defence, I’m no stranger to podcasts and actually this one had been in the works since January and the lockdown has merely hastened its arrival rather than being its origin.

I’m no stranger to podcasts having been interviewed for loads of them at various times, but I’ve certainly never run one so this is a big step up. It is something I’d been considering for quite some time but there were various barriers to getting it going (not least time and some real expertise) when a chance meeting with an old friend suddenly made everything viable.

At a mutual friend’s Christmas party, I couldn’t help but spot the distinctive figure of Iszi Lawrence who I’d not seen in nearly 15 years so went over to say ‘hello’. Iszi was starting out as both a stand-up comedian and an undergraduate student in Bristol back while I was doing my PhD and we lived in the same block of flats. We got on well and hung out a bit and then I jetted off to Germany and we lost touch (this was before Facebook and other things like that) and as so often happens that was the end of a small friendship.

However, as also so often happens, meeting again it was like no time had passed and we were soon chatting nineteen to the dozen and catching up. She’d continued on the comedy circuit and also now runs and hosts several podcasts and radio shows (as well as writing childrens’ books and doing other stuff – find it all here) and we talked about me doing a guest spot on one of the history ones to talk about the early days of palaeontology and cover people like Mary Anning and Gideon Mantell. This though quickly morphed into doing an actual, proper, new and dedicated dinosaur podcast and so here we are.

There are of course, plenty of natural history podcasts, those on palaeontology generally, dinosaurs specifically and all kinds of others. I don’t think there’s real competition between them since it’s not like people can’t listen to them all, but it does immediately beg the question of what’s different or special about this one. I think the answer there is that we are trying to reach a truly lay audience – this isn’t a podcast that’s aimed at dinosaur geeks and nerds or students and academics, or even children – but one for people who like science but may know little more than the names Tyrannosaurs, Triceratops and Diplodocus.

We try and delve into a different subject in each episode and this is aided, in the best possible way, by Iszi’s ignorance. She can steer me to what needs to be said and explained and given context and of course her wit is there to stop me rambling on about gastralia excessively.  Her experience and expertise also means she generally knows how to host and edit one of these things so against all odds I even end up sounding vaguely professional, it’s quite a marvel. If all of the wasn’t incentive enough, we’ve managed to secure a special guest for each episode so alongside comedian Jo Caufield, Richard Herring and Alice Fraser we have historian Tom Holland, podcaster Dan Schreiber, dino-nerd and cake-maker Ralph Attanasia and legendary biologist Chris Packham to ask me some obscure, odd and downright naughty (Richard Herring, inevitably) questions about dinosaurs.

Obviously readers on here won’t normally fit our key target audience but I’d still hope it would be enjoyable to listen to and you’d learn something from it. There’s so much to talk about and explore and recover that it should be appealing no matter your existing levels of knowledge. Do though please share this to anyone who might want a listen and might enjoy it, reaching out well beyond the dino aficionados is a key part of this and you can make a huge difference with a like and share and tweet and whatever. The first two episodes are up right now here on iTunes and on here website here and we’ll be adding one a week for the next few weeks. This is something of an experiment so if we don’t get a good number of followers and subscribers this may be a short series (so consider that either a warning or a blessed relief).

Do give it a try and do give it a share. First episode? Well it could hardly be anything else, could it?

 

Gharials, dinosaurs, sexual selection, dimorphism, communication and conservation

Male (above) and female (below) gharial skulls. Photo courtesy of Larry Witmer.

So, yes, new paper time and which the concept behind this one was quite simple the outcome (as is so often the case) rather spiralled out into a bunch of other, very interesting aspects. As I noted in the run up to this post, I’ve been working a lot on sexual selection and what it means for dinosaurs in particular and wanted to use gharials as the perfect model for dinosaurs but lacked a dataset on these rare animals. A chance post by Larry Witmer led me to contact him about his dataset but it turned out to be only three animals, not the dozens I’d hoped for.

It was though, enough stimulus to get me hunting and with Jordan Mallon roped in with his interest in testing these ideas we just needed to get enough data. Happily, my former undergrad student Patrick Hennessey wanted to get engaged in some research and had time on his hands, so while I e-mailed every museum curator and croc research I could asking for photos of skulls, he set off to visit every collection in the south of the UK that was accessible. Some months later and we had an incredible set of over 100 specimens. We know of more too from photos that lacked scalebars (we were unuseable) or were in museums where we couldn’t get a response from the curator, or had various bits of skin preserved which concealed key bits of data. (We also found a good few mislabelled specimens of Tomistoma while we were at it). Still, 100 is a massive dataset for this kind of work and especially for such a rare animal and this gave us an excellent platform for our analyses.

Digging into the gharial literature though we soon found other issues. Despite the fame of these animals, their rarity means the literature on them is very small and very little is known in detail or was last written about in detail decades ago. To complicate things further, the two distinctive male traits (a fossa on the snout that correlates with the ghara, and a pair of palatal bullae) have never been truly convincingly shown to be definitively male accoutrements. Happily, an analysis of the data did suggest that the fossa was clearly a male feature and the bullae most likely were too.

Moving onto the central point of the project, analysis of the dataset showed that without pre-existing evidence for a given specimen being male or female, discovering any evidence of dimorphism was very hard, even for a dataset of over 100 animals. Gharials are strongly dimorphic in body size but the overlap between larger females and smaller males across much of the data, and the unknown sex of juveniles (which shown neither fossae nor bullae) makes finding this signal impossible. This matches what Jordan and I have said in a previous paper, and suggests that short of very large datasets and / or very strong dimorphsm (even more than seen here) or very good evidence for the sex of most specimens, it will be hard to find. That means that for the average data set we have for even well-represented species of dinosaurs (well under 100 incomplete specimens, no idea of levels of dimorphism but unlikely to be well above what we see in modern species, and no data on sex) we are not going to get a signal on dimorphism even if it’s there. I’m sure dimorphism is common in dinosaurs but I’m also sure we’re not finding it.

Female (left) and male (right) gharial snouts, the latter showing the expansion of the snout and the narial fossa anterior to the opening that makes the nares. Image courtesy of Larry Witmer.

That is, of course, based on things like body size or where a feature is expressed in both sexes (as, for example, ceratopsian fills appear to be). Presence-absence dimorphism (where one sex has a feature the other does not) should still show up relatively clearly with much smaller sets of data, but we’re not aware of any species that would obviously fit this criterion. The fossil record isn’t giving up numerous horn-less Allosaurus or dome-less Pachycephalosaurus specimens and while there are things like the two Khaan specimens with different tail anatomy, it’s just those two for now rather than a nice dataset of a dozen or so. Well-known taxa like Centrosaurus and Coelophysis are distinctly lacking in obvious dimorphism.

All of this is hopefully interesting and important for understanding sexual selection in the fossil record and as a guide for future research, but this work also threw up some interesting information for the gharials themselves which is worthy of comment. First of all, we were able to show that the fossa on the snout which is the correlate for the ghara is strongly positively allometric. This is no big surprise but it’s good confirmation that this feature is under sexual selection, and conforms with the (limited) evidence that the ghara starts growing around the time that these animals become sexually mature. We also note that it likely serves as an honest signal, since it would generate tremendous drag on the tip of the snout and that’s pretty critical for an animal with a super thin and presumably hydrodynamic set of jaws used to catch fish.

Surprisingly though, the bullae don’t show this pattern. They first appear on skulls around the same time as the fossa suggesting they are also linked to reproduction, but they first appear just before the fossa. We suggest that this is because the ghara while still small, may not need a fossa to hold it onto the skull and so the ghara and bullae may start growing at the same time, but the bullae would appear on the skeleton first. The bullae are also not allometric, so while they are larger in larger males, they are not disproportionately larger. This suggest that while they are an important part of the reproductive biology (and presumably as part of the palatal sinuses, potentially in making noise) it might be there merely to indicate sexual maturity rather than be an actual attractor. Either way, these give us some hints about the reproductive biology of these animals which gives us some hypotheses to test.

One last thing we spotted is that the very largest males are quite disproportionately robust. They have unusually wide skulls (including the normally slender snout) and also have very thick teeth, with animals only 20% smaller having teeth about half as thick. To our knowledge this has not been observed before and quite what this means isn’t certain. We hypothesise that these very large individuals might either have especially strong heads and teeth for fighting each other, or perhaps because they are entering a different niche and are able to exploit much larger prey than others. Either way, this points to an important issue given how endangered gharial populations are.

Very young gharials, yet to display any external features that might indicate their sex.

With animals under strong sexual selection, a few individual males will have a disproportionate amount of the mating opportunities in a population. But those males are also likely very well adapted to the prevailing conditions. They have, essentially, a good combination of genes allowing them to grow so big and maintain such a large ghara. If they are operating in a different niche and that isn’t taken into account (they may be eating much larger fish species compared to other gharial for example) when trying to protect them and conserve their habitats, then they might be especially vulnerable. If your genetically best adapted and fittest individuals are at most risk, that’s potentially very bad news and is unlikely to be good for the long term survival and genetic health of the population. This is of course, potentially rather speculative, but it’s supported by what we understand of strong sexual selection and the observations about the largest male skulls. It’s certainly something that is worth checking out in more detail and at the bare minimum it’s an interesting observation about their ontogeny and what that might mean for our taxonomy in the fossil record.

So here ends a very long process to analyse and assess dimorphism in gharials as a model for dinosaurs. It has thrown up far more complexity and nuance, especially in the living species themselves, than I ever thought but that has been in itself most interesting. It only remains for me to thank my coauthors for their contributions on this paper, and the huge number of curators and researchers who generously checked catalogues and sent in photos for us, the paper really would not exist with them all.

Hone, D.W.E., Mallon, J.C., Hennessey, P., & Witmer, L.M. 2020. Ontogeny of a sexually selected structure in an extant archosaur Gavialis gangeticus (Pseudosuchia: Crocodylia) with implications for sexual dimorphism in dinosaurs. Peer J.

 

Sexual selection in dinosaurs, the story so far…

I have a major new paper coming tomorrow on sexual selection in dinosaurs. This is an area in which I have been extremely heavily involved in the last decade and have published numerous papers on this subject with various colleagues, writing about the underlying theory of sexual selection and how it might appear in the fossil record, providing evidence for it and actively testing hypotheses. This has also led into my working on related issues of ontogeny and social behaviour in dinosaurs which feed back into these areas to try and deal with certain aspects that came up as a result of these analyses.

Suffice to say I’m not going to go back over the whole history of my work in the field, or that of plenty of other researchers which is both relevant and important. But a little bit of context is important with respect to the coming paper because it’s something that I’ve had in my mind to do for about as long as I’ve been working on this subject but I didn’t think I’d be able to do because the dataset didn’t exist.

All of the work I have done really tried to get into answer the questions of which features of which dinosaurs may have been operating under sexual selection and can we tell. (More properly, I should say socio-sexual selection since teasing out social dominance signals from sexually selected signals is probably impossible though mostly the two are more or less synonymous in various ways so it’s not a major issue conceptually). The short answer is that really quite a lot of features probably are under some form of sexual selection. We can see this by the fact that we can rule out functional explanations for things like ceratopsian crests as being anchors for muscles attachments, radiators, or for defence because they are highly variable and / or fundamentally don’t work (Elgin et al., 2008; Hone et al., 2012). They are costly traits to grow and lug around (be they stegosaur plates or hadrosaur crests) and so clearly have a fitness cost, ruling out species recognition as a signal (Knell et al., 2012; Hone & Naish, 2013). Similarly, there is no clear pattern of differentiation among sympatric species as would be critical for a recognition trait (Knapp et al. 2018). They are highly variable both within and between species, another hallmark of sexually selected traits (Hone & Naish, 2013; O’Brien et al., 2018) and finally they grow rapidly as animals reach sexual maturity which is absolutely characteristic of sexual selection (Hone et al., 2016; O’Brien et al., 2018).

The one issue that has remained elusive in all of this is the vexed issue of dimorphism. This has proven very hard to detect for a variety of reasons, but most notably the generally small sample sizes we have for dinosaurs and the tendency for males and females to overlap in size and morphology over much of their lifespan (Hone & Mallon, 2017). To top it off, mutual sexual selection can reduce or even eliminate dimorphism making it harder still to detect and meaning even an apparent absence of it, does not mean sexual selection is not in operation (Hone et al., 2012).

It would be nice to be able to explore the issue of dimorphism in particular in more detail with an extant analogue. Plenty of comparisons have been made to various living taxa in terms of dimorphism (be it body size or major features like a crest or sail) but they run into various issues. Mammals are nice and big and often have things like horns that differ between males and females (either in shape or presence / absence), but they’re phylogenetically very distinct and have the problem of growing quickly to adult size and staying there. Lizards offer something interesting with some dimorphic species with various signal structures (like some chameleons) but then while they are reptiles, most are small and the biggest varanids have no sexually selected structures. Birds are obviously literally dinosaurs but have a mammalian-like growth and are not very big. While there’s plenty of size dimorphism in them, there are few that have obviously dimorphic traits that would show up in the skeleton (like horns).

That leaves the crocodylians, which are off to a good start. Some are very large and take a long time to grown to adult size, all are egg layers, they are sexually mature long before full size meaning they would likely express sexually selected traits while still quite small (like dinosaurs and unlike birds or mammals), and a number are also sexually dimorphic in body size. The only thing missing is some kind of sexually selected bony feature, or at least one with a clear osteological correlate.

And so to the gharials, the wonderfully weird crocodylians of the Indian subcontinent which tick every single one of these boxes right down to the growth on the snout of males, the ghara, that is absent in the females. This has long been obviously the one taxon that ticks pretty much every possible box and would provide an excellent living model to analyse and see how easy (or not) dimorphism is to detect when you have a known dataset to work from. The obvious limit to this plan is that these animals are extremely rare and most museums have few, if any, specimens. The one species that was pretty much perfect for my plans immediately fell out of contention because I couldn’t see how I could get a dataset together that would be sufficient for analysis, so the idea was shelved. Until recently…

Obviously, to be continued.

 

Papers on sexual selection, dimoprhism, socio-sexual signaling, social behaviours and related subjects in fossil reptiles:

O’Brien, D.M., Allen, C.E., Van Kleeck, M.J., Hone, D.W.E., Knell, R.J., Knapp, A., Christiansen, S., & Emlen, D.J. 2018. On the evolution of extreme structures: static scaling and the function of sexually selected signals. Animal Behaviour.

Knapp, A., Knell, R.J., Farke, A.A., Loewen, M.A., & Hone, D.W.E. 2018. Patterns of divergence in the morphology of ceratopsian dinosaurs: sympatry is not a driver of ornament evolution. Proceedings of the Royal Society, Series B.

Hone, D.W.E., & Mallon, J.C. 2017. Protracted growth impedes the detection of sexual dimorphism in non-avian dinosaurs. Palaeontology, 60: 535-545.

Hone, D.W.E., Wood, D., & Knell, R.J. 2016. Positive allometry for exaggerated structures in the ceratopsian dinosaur Protoceratops andrewsi supports socio-sexual signaling. Palaeontologia Electronica, 19.1.5A.

Hone, D.W.E. & Faulkes, C.J. 2014. A proposed framework for establishing and evaluating hypotheses about the behaviour of extinct organisms. Journal of Zoology, 292: 260-267.

Hone, D.W.E., & Naish, D. 2013. The ‘species recognition hypothesis’ does not explain the presence and evolution of exaggerated structures in non-avialan dinosaurs. Journal of Zoology, 290: 172-180.

Knell, R., Naish, D., Tompkins, J.L. & Hone, D.W.E. 2013. Is sexual selection defined by dimorphism alone? A reply to Padian & Horner. Trends in Ecology & Evolution, 28: 250-251.

Knell, R., Naish, D., Tompkins, J.L. & Hone, D.W.E. 2013. Sexual selection in prehistoric animals: detection and implications. Trends in Ecology and Evolution, 28: 38-47.

Hone, D.W.E., Naish, D. & Cuthill, I.C. 2012. Does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs? Lethaia, 45: 139-156.

Taylor, M.T., Hone, D.W.E., Wedel, M.J. & Naish, D. 2011. The long necks of sauropods did not evolve primarily through sexual selection. Journal of Zoology, 285: 150-161.

Elgin, R.A., Grau, C., Palmer, C., Hone, D.W.E., Greenwell, D. & Benton, M.J. 2008. Aerodynamic characters of the cranial crest in Pteranodon. Zitteliana B, 28: 169-176.

 

 

Books to read to become a palaeontologist

Despite (or because of) writing a long piece on ‘how to become a palaeontologist’, I still get loads of questions from people who want help and advice about getting into this field. While I encouraged people to read a lot, I didn’t get too specific since everyone has different backgrounds and areas they want to get into, and books (especially on dinosaurs) come out in a huge flurry and tend to date quickly. However, a recent query and some pondering led me to realise that actually there’s a core group of books I would recommend which is likely to be a useful starting point years or even decades from now (and indeed, many of the books are already decades old).

What may surprise people is that basically there’s no dinosaurs on the list and not really any palaeontology. This is because people who want to learn about palaeontology, whether just because they are interested, or because they have an active plan to becomes one, tend to get really obsessed with facts. Learning lists of formations and dates and faunal lists and how many teeth a species have are useful, but this use is limited. This stuff constantly changes and gets out of date and if you don’t know it or forget it, you can always look up the answer. What is infinitely more useful, is understanding – a knowledge of the principles at play and the fundamental basis of how organisms and systems work, and how we obtain and apply that knowledge.

In other words, reading dinosaurs books is a poor way to learn about palaeontology (in some ways, I’m obviously not suggesting someone who wants to work on dinosaurs shouldn’t read books on dinosaurs or learn about them). So with that in mind, here’s my list of ten books to read to get into palaeontology. I should stress that this is very far from exhaustive and it’s skewed to books in areas that I am interested in, and as a result there’s not a lot of geology in there. Still, at least ¾ of this list will be useful for anyone wanting to embark on a palaeontological career or just getting a better understanding of the field, or for that matter almost any are of biology.

These are presented in a rough order in which to read them where I think they would most benefit and build on each other, though equally that is far from important and it wouldn’t really be an issue to read them in a random order.

 

  1. Charles Darwin – Origin of Species

If I’m honest, it’s pretty tedious and repetitive as a book to read (the Victorian style of popular science writing doesn’t necessarily hold up too well 150 years later) but it can hardly be avoided. It’s so fundamental to the basis of modern evolutionary theory as well as being so important historically that even if it’s a slog to get through, any wannabe biologist of any stripe should read it.

  1. Richard Dawkins – Selfish Gene

A modern classic and important to understand the role and important of genetics in evolution. As such it’s an important successor to The Origin and is also something of a period piece for the state of biology and evolution when it was written.

  1. Carl Zimmer – Evolution

A few years old now, but an excellent introduction to modern evolutionary theory and its foundations and a very good place to start for anyone wanting to learn anything in depth about biology.

  1. Bill Bryson – A Short History of Nearly Everything

For me the best ever popular science book. This is a brilliant grounding in both the basics of science (geology, physics, chemistry and biology) as told through the history of those fields with input from a huge number of respected authorities in their fields. I reread it every year or so.

  1. Steven Levitt and Stephen Dubner – Freakonomics

Something of a wildcard this, it’s not without issues, but it’s a very entertaining read and it shows well that with careful thought you can make the most of almost any dataset to say something meaningful about a subject. With data at a real premium in palaeontology, a book on creative analysis (which is also a lot of fun) from limited informationis something rather useful.

  1. Ben Goldacre – Bad Science

All the examples might be medical, but this really is an exemplary book on how experiments should be set up and how things should be analysed. It’s a wonderfully easy read and while it’s not about statistics per se, it does really get to the root of preparing and planning your work and understanding what you can and cannot grasp from data, as well as how people mishandle and misinterpret results.

  1. Armand Marie Leroi – Mutants

An absolute favourite of mine and the book that got me to be interested in, and understand, development. A wonderfully written book and deeply engrossing and linking together human biology, development, genetics and history.

  1. Paul Colinvaux – Why Big, Fierce Animals are Rare

This book is slowly aging but as an introduction to population ecology it’s still excellent and provides an excellent foundation for understanding so much of the pressures that influence organisms.

  1. Matt Ridley – The Red Queen

A brilliant and perennially popular book on sex and sexual selection and its importance in shaping evolution, diversity anatomy and behaviours. A must read if you want to understand a selective driver than can be even more powerful than natural selection.

  1. Neil Shubin – Your Inner Fish

The closes this list probably comes to palaeontology, this book explores the world of EvoDevo and the increasingly important role palaeontology plays in other branches of biology to understand evolution and deep time. It also covers some major palaeontological discoveries and advancements in the field so is rather a 2 for 1 in that sense.

 

And an extra bonus number 11 that is actually (a bit) on dinosaurs

  1. Deborah Cadbury – The Dinosaur Hunters

Wonderfully written book on the story of the origins of palaeontology as a science and featuring Owen, Mantell, Buckland, Anning and plenty of others. This is pretty much a historical book, but having an appreciation for the origins of the field and science of the time is important and useful to know and this is a very compelling read.

Can we make pterosaur planes yet?

Short answer, no, longer answer, maybe one day but there is at least some cool potential here. That’s the basic gist of a new paper I have out today with Liz Martin-Silverstone and Mike Habib on flight in the fossil record and its implications for aircraft design.

Back in the earliest days of human-powered flight there was an inevitable draw to birds for inspiration as heavier than air fliers, and there’s more than enough videos of cranky machines flopping around on their wings failing to get off the ground if you are into that sort of thing. Aerospace technology has moved on though and bird-like flying machines (called ornithopters) do now exist. More and more technology takes inspiration from living organisms (biomemetics, bioinspired tech) and when it comes to flight, so often at the forefront of engineering, this has included all manner of bits of bird and feather-like features. Bats have played a lesser role too and insects are increasingly looked at since now aircraft do not have to have pilots and remote controlled craft, drones, autonomous vehicles (and plenty of other names and acronyms) are increasing in number and diversifying in form.

Amidst all of this, the fossil record goes almost unnoticed. Flying organisms have all manner of adaptations for weight reduction, streamlining, ways of manipulating lift, drag and control and of structural support with unusual forces and combining issues like take-off and landing on usual surfaces with having to actually fly. They provide known working models that can be directly copies and mimicked, or at least used as a starting point to investigate ideas. Given the plethora of flying animals in the fossil record (both gliders and powered fliers) that have no living analogues, these would seem an excellent place to seek out new technological innovations and ideas and the idea of this paper is to try and trigger some interest in this. True, people have looked at pterosaur flight, though mostly to see how pterosaurs might have flown. Only a very limited amount of work has been done looking at these as possible aircraft models and even then it’s been holistic with no real look at the details of wing construction or control. And this is just one clade and ignores things like Yi, with its combination of membranes and feathers, Microraptor with its multiple control surfaces, Sharovipteryx the delta-winged glider and others.

The paper is short though and writing such a piece that is trying to work for engineers with potentially little knowledge of biology, biomechanicists with little knowledge of palaeontology and palaeontologists with little knowledge of either. As a result, it’s rather superficial in terms of its treatment of many ideas and concepts despite a vast amount of cited literature (we had to get dispensation for the editor to include so many and the referees were still unhappy and wanted more) but it does hopefully provide some real information and ideas for these three groups of researchers to come together and make use of the palaeontological resources at their disposal.

So while we might not see any pterosaur-based drones around anytime soon (or indeed ever) we hopefully will see considerably more interest in flying animals in the fossil record on all sides and this certainly has the potential to feed back into new designs. I’d obviously love to see an azhdarchid drone that can walk, run, launch and fly but even seeing something like an anctinofibril-based system of wing warping or pteroid-supported propatagium would be super cool. Stanger bits of the biological world have been looked at for engineering and hopefully various fossils will become a part of this in the near future.

 

Martin-Silverstone, E., Habib, M.B., & Hone, D.W.E. 2020. Volant fossil vertebrates: potential for bioinspired flight technology. Trends in Ecology and Evolution.

Note: this has gone live a week earlier than we were told to expect and the version out there is currently the uncorrected proof, and while we didn’t make any substantive changes, a better version of this should follow.

Big wings in the Solnhofen

The Solnhofen limestones of Bavaria are famous for their well-preserved fossils and for a pterosaurs researcher, the plethora of specimens and taxa that are represented. Finds continue to this day and we now have more species known from more specimens than ever before, including from a variety of a branches of the pterosaurian tree. The Late Jurassic was an interesting time with the pterodactyloids diversifying, the non-pterodactyloids soon to fade (though doing pretty well) and a few intermediates (wukongopterids, or if you prefer, darwinopterids) are still about. One thing that is true of all of them though is that they are not very big.

While later pterosaurs are famous for producing numerous lineages with wingspans well in excess of 4 and 5 meters and all the way up to 10, before the Cretaceous, there’s basically nothing that even gets up to 2 m in wingspan, and even those tend to be relative giants and quite rare. This is especially true of the Jurassic pterodactyloids which really don’t seem to have got going yet in the size stakes. However, there are some tanatalising hints of bigger individuals or even big species with various bits of limb elements (and slightly bizarrely, some isolated but articulated feet). Not much has been done with these in part because they tend to be very incomplete.

However, quite a few years ago now, Dino Frey at the Karlshue museum in Germany acquired a complete and articulated wing of a large Solnhofen pterodactyloid. It was much bigger than any other known complete wing and it eventually feel to Ross Elgin (then a PhD student under Dino and myself) to work on. We started on this and worked up a manuscript and then sometime later I happened to be in Berlin and spotted on the wall of the collections, another, equally large (though rather less complete and less well preserved) Solnhofen wing. This has apparently sat all but ignored for many years and as far as we can tell, it’s never featured in any paper or been referred to before. So now we had two wings to describe, each of which would have been from an animal with a wingspan of just over 2 m and they turned out to be pretty similar to each other, but what were they?

Working out what they were took some work. After all, it’s perfectly possible that these represent known taxa, but are merely unusually large individuals. And with only the wings to go from, a lot of the anatomical data you would normally want from the skull or some gross proportions of the neck, legs and so on are missing. To make it more awkward, we don’t have a great understanding of the growth patterns of many pterosaurs so it’s not obviously what the trajectories might be of the rarer species where we have only a few specimens.

Looking in detail at our two wings and various other larger Solnhofen pterodactyloids and other isolated large wings showed that these two new ones are different to each other and there are likely two different ‘big wing’ morphs present. A number of major pterodactyloid clades are either around or at least suspected to be present in the Jurassic, and so there was a wide range of possible candidates. However, the anatomy present ruled out most of them (ornithocheiroids, istiodactyloids, azhdarchoids) though it did leave the identity uncertain and they could be ctenochasmatids or very early dsungaripterids.

So while we don’t know exactly what we have here (and we suspect there’s a new taxon in this material based on some unusual features of the Karlsruhe specimen) it is still interesting stuff. We now have a good record of all the largest Jurassic pterodactyloids and clear evidence of animals of over 2 m wingspan. We also have much more detailed information on their anatomy and while the exact identities are uncertain, it looks like there is more diversity here than previously realised and that there are more taxa to be discovered. New specimens are still being uncovered in the Solnhofen so hopefully it is only a matter of time until we have complete, large, pterodactyloids before the Cretaceous.

The paper is open access and fully available here.

Elgin, R.A. & Hone, D.W.E. 2020. A review of two large Jurassic pterodactyloid specimens from the Solnhofen of southern Germany. Palaeontologica Electronica.

Toronto Zoo

Snow leopard

Take a long drive (or in my case, an interminable bus ride at the end of a subway line) north of Toronto and you eventually come to the zoo. Thus despite the name this is not a city zoo but one very much out in, and even beyond, the suburbs (wild turkeys were present alongside the bison for example). As such it’s a very large zoo, which is always nice when it means that the larger animals have a lot of space but be prepared for a good workout with some decent hills thrown in too.

One nice hallmark of the zoo was the extensive collection of ‘local’ species – groups of both prairie bison and the wood bison subspecies (your definitions may vary), moose, bobcat, wolves, polar bear, snowy owls and Arctic fox (a new species for me) and others were all present and correct. Indeed, the polar bears were about as well kept as I’ve ever seen and one in particular was taking great delight in sliding down the snowy banks of the hill in its enclosure and rolling around in the snow. Much as LA Zoo makes great use of the local weather to keep lots of tropical species outside, Toronto does well in the same vein with cold weather species with things like snow leopards and ibex in addition to the Canadian animals.

Giant African soft-shell

They do though also have lots of more ‘traditional’ species and it’s rather neat to see white lions, rhinos and hyenas in the snow. Of particular interest though were the several walk-through tropical and temperate houses that had some especially neat animals. One house was linked to various species that had access inside and out including relative locals like beaver (sadly not visible) and grey shrike. It was especially cool to see the extremely rare black footed ferret though this spot was tempered somewhat by the fact that it was only visible as a sleeping ball of fluff.

I also got to tag some other species that have loomed a long time on my list of animals I wanted to see. First off was a pair of wombats which were everything I’d wanted and even were good enough to move around a bit and nearby in the Australian section were some galah cockatoos which was neat to see too. Sadly, the allegedly existing but not actually visible short-beaked echidna repeated the trick of it’s conspecific in the Berlin Tierpark and was underground and invisible.

Tentacled snake

On the upside though I did get two more stellar reptiles and both in the larger walk-through house that included pygmy hippos, crocodiles and numerous birds. First off a tentacled snake which was kind enough to sit near the glass allowing me to get a decent photo of this essentially aquatic animal. The second was another aquatic specialist, an African soft shelled terrapin. It was a huge one and much larger than I’d expected and was sat out on the bank but did extend and retract its neck which was fascinating to watch.

All in all, it’s a very good zoo, but be prepared for a long day and a decent hike. Even skipping some of the more distant parts of the zoo will still involve a healthy bit of exercise but it’s a great collection and, rarely, one that is very rewarding to visit in the deep of winter.

Wombat!

 

 

 

A little more Luchibang

Life reconstruction of Luchibang by Matt Van Rooijen

After the previous mammoth post on the long and painful history of the publication of the new paper, I still wanted to write a little more about the specimen and what we have learned. As noted in the first post this specimen is preserved alongside a couple of fish and apparently has some soft tissues associated with it.

The istiodactylids are one of those groups where their ecology has been very uncertain with a variety of activities suggested. Based on their affinities with the highly piscivorous ornithocheiroids it’s been suggested they were fish eaters, though their teeth don’t look well suited to catching fish at all, and that little cluster of interdigitating and cutting teeth has been used to put them forwards as scavengers. That doesn’t sit too well either since they appear to generally be quite aquatic in their habits and while we have a great many birds that are specialist scavengers today, none of them are marine soarers.

Luchibang doesn’t actually help resolve this much. While it’s limb proportions and especially long legs point to greater terrestrial competence and might point to an animal that is therefore scavenging more, it’s also preserved with two fish specimens. One of these is down and under the ribs and apparently in the ribcage. In the paper we are cautious over this specimen as small fish are commonly associated with these kinds of Liaoning specimens (indeed, there’s one already here by the head which clearly wasn’t’ eaten) but it is certainly possible that it represented preserved stomach contents.

So we can provide some tentative evidence to support both scavenging and piscivory in this animal (and of course these are not mutually exclusive positions) and so while what we have here is interesting it doesn’t resolve much. This uncertainty is reflected in the very nice life reconstruction that Matt Van Rooijen kindly did for the paper (quite a few years ago now, he’s been sat on it a while!). In the foreground Luchibang is wading in the shallow waters and grabbing a fish while nearby is the carcass of an iguanodontian which is available as an alternate source of sustenance.

One last thing to comment on is the preservation of soft material on the specimen that we interpret as soft tissues. It is really rather poorly preserved and is little more than some stains on the rock but with some regular patterning and shape that appears to be organic. There are several spots and they all look similar and are associated with the skull, the neck and the ulnae. They don’t appear to be parts of the wings suggesting these are skin traces. There’s no indications of any pycnofibers but then, assuming these are soft tissues, they are rather decayed.

That’s quite enough on Luchibang for now, the paper is fully open access so you can read the full description and discussion there. This only leaves me to thank Matt for his artwork, my coauthors and the referees and editors on this paper.

 

 


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