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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.

How to build a dinosaur

As I noted yesterday, the latest Planet Dinosaur was just one of a whole suite of shows on the BBC that ran on Wednesday. The second was a one-shot on BBC 4 with the above title and it was basically a behind-the-scenes of putting together an exhibition (the new one at the LA County Museum) backed by various little side routes about the issues of reconstructing dinosaurs based on incomplete remains from the ground to the museum hall.

Now I must confess I have a big bias towards this show as it was hosted by a friend of mine and featured a number of friends and colleagues including Darren Naish and John Hutchinson. Still, trying to be impartial, I did like it and I think it brought forward a number of things that I’ve never really seen before on a dinosaur show – the decisions that go into posting mounts, reconstructing missing bones, and so on.It was a bit simple in places, but that’s really to be expected for something aimed at a very general audience. Certainly I suspect it made people think about issues they had probably never really considered before.

My one real criticism would be that it was a bit disjointed. Everything covered was relevant, but there was no really clear thrust of how it all fitted together. A minute at the beginning and end laying out what we were about to see and how it fitted into the big picture.

While obviously not his fault, Darren’s piece about Xenoposeidon was rather odd, and makes this point. Certainly it’s nice to show how things can be rediscovered in basements and newly recognised in the light of new research and people seeing things with fresh eyes. it makes the point about keeping collections and documenting them properly, the difficulties of taxonomy and working from incomplete material. But it doesn’t really tell you anything about building a dinosaur and so doesn’t really fit the rest of the show, regardless of how good it was.

In short though it was a good quick round of various aspects of the public face of palaeontology and how researchers get there. A little light perhaps, but well rounded and certainly containing some nice, rarely seen aspects that would certainly inform many a casual viewer.

Guest Post: How to collect a skeleton from a cliff face with 200 meters of sandstone as overburden

Reconstruction of Seitaad ruessi. Image courtesy of Mark Loewen.

Some of you may have already spotted the new paper out covering the delightful little Seitaad ruessi – a brand new sauropodomorph from the Middle Jurassic of Utah. (Some coverage is here if you have missed it, and the paper is freely available here).  Mark Loewen, one of the authors of the new paper, tells of how the material was found and then how they got the specimen out of the quarry:

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The complete ‘how to’ guide for young researchers (so far)

It seems that recently some of my various ‘how to’ posts have been found by various search engines and readers and since I don’t have much to write about today and that these are, I think, some of the most important and beast things I have written, it seemed a pertinent time to resurrect them under a single banner for any more recent followers who have yet to0 find them. For those who have missed out, I wrote an extended series of posts covering all the basic skills of research such as writing and reviewing papers, giving talks, editing work and so on. These I hope have been and will continue to be of use to students and young graduates trying to break into science or generally improve their skills during their education, so here I have bundled them all up into one single slot to make it more accessible and easier to link to as well as hopefully bring this to the attention of new Musings readers.

Basic advice to young researchers

How to complete a PhD

How to get hold of papers

How to write a paper (and get it published)

How to contribute to a paper

How to review a paper

How to edit a volume of papers

How to write a conference abstract

Things to do at a meeting

How to give a talk

How to make a scientific poster

How to arrange a meeting

A ‘how to’ summary (contains various updates and links to other sites)

And finally don’t forget the ‘science basics‘ section on here which contains all of these and more.

Do make use of these and feel free to pass them on to your colleagues / friends / students and do add comments to help keep them thorough and up-to-date. The feedback I have had on these has been very good, so I’m happy to be confident that they are doing some good.

A ‘how to’ summary.

This latest week-long series of posts on ‘how to’ do various things (combined with other earlier ones) seems to have generated a few comments (overwhelmingly positive, I am pleased to see) and have been read by a great many people (hits over the last week in general, and for the specific posts have been way above my normal averages). Between these points and few other things that have cropped up, it seemed well worth adding a short off the cuff summary to what all of this has been about and what I tried to achieve with these posts (and I hope to have more in the future). Continue reading ‘A ‘how to’ summary.’

How to arrange a meeting

Munich, 2007

Flugsaurier: Munich, 2007

As part of the big stream of ‘meeting’ based posts, it seemed worthwhile to talk about how to go about arranging a meeting or conference. This will be the last one the in current run (with a summary / review coming tomorrow after your normal dose of AABQOTW)so enjoy it while you can! The Wellnhofer meeting was in hindsight not too bad, but the sheer number of details, the lack of preparation time (11 months is *not* enough) and the fact that it was in Munich and basically I don’t speak German made it all the harder. I did get a considerable amount of help from my institution but I basically had to do everything on my own in terms of planning and basic execution. If you have a years run up, speak the language of the country you are in, and get some decent help it should be fine. However, a check list and a few dos and don’ts probably won’t go amiss:

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How to give a talk

rey-symposium_munich_231Although meetings and conferences are about far more than just giving public talks, they are of course a central theme. For the scientist, it’s a chance to present his information to his peers to disseminate his ideas and research, and of course trigger feedback and new research. For the audience, it’s an opportunity to gain access to information and ideas perhaps years ahead of their formal publication, (and some will never be published) and to get access to people and branches of research far outside what they can get in their own institutions of even countries or continents if it’s a big meeting. It seems odd then that I had had to sit through a great many talks that were obtuse, dull, confusing or apparently pointless. It seems a simple enough skill (especially in a profession at the core of which is communication and for which lectures and teaching form such a prominent position) yet is clearly one to be valued and improved if possible. (Image courtesy of Luis Rey).

There are naturally good and bad speakers, and it’s always going to be hard for someone who works on gastralia in theropods to interest someone working on the behaviour of Permian fishes, but the simple errors and mistakes we can at least try to deal with. As ever in these guides, most of this information is simple, straightforward and probably obvious – but enough people don’t seem to realise it so I might as well put down my 2c:

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How to make a scientific poster

Conference posters are in theory really simple – stick a few words and pictures about your work on a bit of paper, print it out, stick it on a wall and be done with it, but I have seen a great many terrible posters that need not have been terrible. As with the rest of this series, many, if not all, of the points raised might seem obvious, but then if so, why are there often so many awful efforts out there? This should therefore at least serve as a reminder and with luck will also provide some advice and hints to at least a few people.

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How to write a scientific conference abstract

Continuing with my “How to” posts (also known by some as “Dave states the bleedin’ obvious”) this time I want to take a few wild swipes at abstract writing. The conference season will soon be upon us, so these next few posts will all be about various aspects of meetings, conferences and symposia. Abstracts are of course critical to meetings and conferences, whether small internal ones, or major international ones. As ever, most of these points should be pretty obvious, but that does not seem to stop endless numbers of people ignoring them and making major mistakes or having their abstracts rejected. I’ll actually be posting about presenting posters and talks in the future, as well as another list of blindingly obvious things to do when you are actually at the conference. Right, onto the abstract:

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How to contribute to a paper

This one is rather off-centre, but my guess is that it might well be useful for some students. I think most people get their first papers published either working alone, or by collaborating with their supervisors or perhaps another PhD student, and thus you are in a familiar environment with people you know well. It can be intimidating to contribute to a paper with a couple of senior researchers or even to try and handle a big research group on your own as a senior author on a paper. While this micro-guide is aimed at the former situation, it should also serve to help with the latter as well.

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How to review a paper

Continuing with the important theme of academic research and publishing it seemed high time I deal with the opposite side of writing a paper which is reviewing one. This should serve as a guide for those asked to referee a paper without much or any experience, and also for those simply trying to get a paper written and get it past the referees – it often helps to know what is going on on that side of the publishing ‘wall’ as it will help you deal with editors, referee’s comments and so on.

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How to edit a volume of papers

With the Wellnhofer volume now with the printers (not long now people – please spread the word) it seemed an appropriate time to revisit some of the basics of science publishing that I began with advice on how to publish a paper and complete a PhD. Now let’s take a look on the other side of the fence from the perspective of the people who deal with those papers. Coming soon will be my take on how to review a paper, but we will start with how to edit a volume.

Continue reading ‘How to edit a volume of papers’

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