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?

 

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.

 

 

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.

Sauropod digestion suggestion

I do not normally go in for speculative pieces on the blog and when I have ideas about Mesozoic biology I tend to try and get an excuse to write a paper about them or consult with some colleagues and see what merit the ideas may have. But something popped into my head the other day and it’s been rattling around and I thought it would be fun to put it out there into internet land.

First off, I’ll preface what follows with the important point I’m no real expert on the details of sauropod physiology and digestive biology. So it’s quite possible that I’ve missed some major discussions on this in the literature (or online) be it that the idea is already out there and this isn’t new, or it’s already been discussed and dismissed. I’d also add that while I’ll discuss sauropods here, the central issue may also apply to sauropodomorphs, various other ornithischians and potentially even the bigger herbivorous theropods. I’ll try and boil down the argument as simply as possible, though of course I’m deliberately skipping a lot of nuance.

In short:

Big sauropods would need to eat a lot but allowing for thermal inertia, long digestion times with higher efficiency, and reduced metabolism at large size they have the potential to function without eating 24 hours a day.

For juveniles though, they lack some of these benefits and especially would not have the benefits of long digestion times to break down tough plants. They’d have (proportionally) higher metabolisms and would be getting less return from what they ate.

One solution to this would be coprophagy. And yes, that is what you think it is.

Elephants are a good example here (well without the XXXXeating bit) since they eat a lot of rough material like dried grasses and tree bark. They are bulk feeders cramming everything in, stripping out the nutrition they can and moving on. I was warned years ago when working at a zoo that if offered an apple when visiting the elephant house not to take it. Apparently these occasionally passed through untouched and then would be handed out to unknowing guests. The point is, elephant dung contains a lot of undigested material. If you are a young sauropod, something like that which has already passed through your system and is starting to be broken down could, second time round me a lot more nutritious. And you don’t have to go anywhere to find it, it’s a ready source of calories right there.

That really is the limit of my suggestion. As I say, I suspect I’ve missed something important but I can see an obvious few benefits from this and there’s a good few animals that go in for this practice so it has plenty of precedent. I recognise that reptile and bird waste is often very different from mammals, but then we don’t have many 5 ton lizards that eat ferns around for a comparison and the waste of large tortoises certain can contain plenty of grass shards.

Thoughts below, and if I’ve stumbled across a good idea here I’d be happy to try and expand on it.

Late 2019 roundup

I do try to do a roundup of each year and even with the Musings being more and more infrequently updated, I wanted to keep this up. The year has been very slow so not too much has happened in terms of publications or other news and the major even (the naming of Cryodrakon) I did manage to give some good coverage. My only other publication was a response paper written with Tom Holtz that argued (again) that some of the evidence suggested for highly aquatic lifestyles of various spinosaurs are overstated or at least much more complex than sometimes stated. Once again (see also adult dinosaurs, social behaviour etc.) this is at least in part an issue of definitions and the turn of phrase ‘semi aquatic’ which covers a vast range of behaviours and selective pressures and degrees of adaptation being used without anything like enough specificity.

I do now have a whole bunch of papers in review and a couple that are (provisionally at least) accepted and should be out this year, and so while the Musings is likely to carry on being generally quiet there will be some research to talk about with any luck. Most of that will be pterosaurian in nature but there’s some dinosaur stuff in the works as well.

Also coming at some indeterminate point are some new books. I’ve all but finished a first draft for my next popular science book that should be out sometime this year (probably late autumn) and I’m also involved in a couple of others so stay tuned.

In the meantime I am still posting photographs and micro-updates on projects on my Facebook page and this is the best place to keep up day to day, but I’ve no intention of shutting down the blog even if the posts will be sporadic.

Happy New Year.

 

 

Hone, D.W., Habib, M.B. and Therrien, F., 2019. Cryodrakon boreas, gen. et sp. nov., a Late Cretaceous Canadian Azhdarchid Pterosaur. Journal of Vertebrate Paleontology, 39(3), p.e1649681.

Hone, D.W.E. and Holtz T.R., 2019. Comment on: Aquatic adaptation in the skull of carnivorous dinosaurs (Theropoda: Spinosauridae) and the evolution of aquatic habits in spinosaurids. 93: 275-284. Cretaceous Research.

(Somewhat late) roundup of 2018

Lots of people are doing little end of the year reviews and with my general decrease in blogging in recent months this seemed a good motivation for me to do something similar if a bit later than everyone else.

It has been a fairly productive year for me research wise though there are lots more things that are nearing completion or are already out for review so hopefully the next couple of years will show a better return. Even the list below is inevitably a bit warped as some of these papers are effectively in press so will likely end up with a 2019 date on them, while others were out in 2017 but only now have a year appended.

First off are a few on the subject of trophic interactiosn between species. Most recently has been my paper on a Pteranodon with a shark tooth stuck in it, though this year also brough some theropod bite marks on juvenile dinosaurs. There was a rather broken peice of centrosaur frill that not nipped by something small itself, but more interestingly was a rather savaged juvenile diplodocid femur from Dinosaur National Monument. This one had bites very reminiscent of those made by derived tyrannosaurs at a time when they were not around suggesting simialr feeding mechanisms might have been present more extensively in big theropods and the paper also included some work on the issues of identifing ‘biters’ too.

My work on sexual selection and signaling also continued with two papers on this subject. First came one which is the first piece of work by my PhD student Andy Knapp looking at the evolution and changes in the horns and frills of various ceratopsians. This specifically targeted the idea that these things might have evolved as recognition signals but there was no evidence that these eveolved in response to sympatry (being in the same place so where you might want to be different to avoid confusion) and thus supporting the idea that they were more likely under sociosexual selection. Second in this area was work led by Devin O’Brien on the way things like ceratopsian frills grow which can be an indicator of sexual selection. This has been used in one form or another for years but this papers made things more rigorous in the use of reference traits for comparisons to sexually selected traits and marking out other things that also grow fast but are naturally selected.

Finally there’s a couple of papers that don’t really fit into either category. First there’s some work I was involved in looking at the exceptional preservation of dinosaur ‘dandruff’ and the implications that this brings about their biology. Second was a revision of the pterosaur genus Noripterus which has a complex taxonomic history and has suffered through most of the key material being lost. That turning up again allowed proper clarification over the definition of the taxon and a number of other genera that has been referred (os should have been to it).

So all in all a fairly productive time with a couple of my main research themes keeping pace while continuing to work on some other important areas. On the outreach front I continue to do lots of talks and school visits as well as podcasts and some consulting for various TV shows and the odd appearance. The Guardian cancelled their science blog network which ended the Lost Worlds, though it means I am doing more blogging here again as a result. Finally, an early 2019 addition was the creation of a Facebook page for my work and outreach which does a different job to both these pages and Twitter so do please follow me there too.

• Hone, D.W.E., Witton, M. P., & Habib, M.B. 2018. Evidence for the Cretaceous shark Cretoxyrhina mantelli feeding on the pterosaur Pteranodon from the Niobrara Formation. Peer J.
• Hone, D.W.E., Tanke, D.H., & Brown, C.M. 2018. Bite marks on the frill of a juvenile Centrosaurus from the Late Cretaceous Dinosaur Provincial Park Formation, Alberta, Canada. Peer J.
• 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.
• McNamara, M.E., Zhang, F., Kearns, S.L., Orr, P.J., Toulouse, A., Foley, T., Hone, D.W.E., Rogers, C.S., Benton, M.J., Johnson, D., Xu, X., & Zhou, Z. 2018. Exceptionally preserved skin structure reveals the coevolution of skin, feathers and metabolism in feathered dinosaurs and early birds. Nature communications.
• 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., & Chure, D.J. 2018. Difficulties in assigning trace makers from theropodan bite marks: an example from a young diplodocoid sauropod. Lethaia.
• Hone, D.W.E., Jiang, S., & Xu, X. 2018. A taxonomic revision of Noripterus complicidens (Young, 1973) and Asian members of Dsungaripteridae. Geological Society of London, Special Volume, 149-157

Testing for sexual selection

I had a new paper out a few weeks ago but it was at the very height of my busy start to teaching and so barely even got a tweet out about it and completely failed to do anything on here. That’s a shame as this is a paper that has some serious and major implications for trying to detect sexually selected structures in extinct animals (and indeed looking at some odd structures in living ones too). I’ve written a huge amount about dinosaur dimorphism and sexual selection and with numerous papers covering different aspects of the evolution and behviour of dinosaurs (and pterosaus) when it comes to signals and sexually selected things like crests, spines and horns.

The short version is that these are of course hard to look at becuase we can’t directly observe behaviour in extinct animals and coupled with small sample sizes, taxonomic uncertainty of specimens and then issues like extended growth periods and cryptic dimorphism and this is a frustratingly tricky subject to tackle. One standard, if imperfect, measure has been to look at the growth trajectory of the anatomical feature in question and to see if it grows more rapidly than the rest of the naimal, especially iof this happens relatively late in ontogeny. In short, animals don’t need sexaul display structures when they are not sexually mature but when they are this is important so things like horns tend to be small for a long time and then grow very quickly.

This paper led by Devin O’Brien and featuring a host of sexaul selection theroists and biologists posits that things may be more complex still. Features that directly rate to body size will be postively allometric (this can include things like horns and crests in dinosaurs) but those that are not (like say a moths’ antenna), will not. The former are accurate representations of the animals they are attached to and so act as a proxy for their size and quality, but other traits that can still be variable and under sexual selection are not acting in this way and so wouldn’t follow this pattern. There may even be some allometry in these latter traits (non-reproducing animals will not likely invest in such features until the can mate) but the allometry will be much greater, and the correlation with body size present in visual signals.

To help resolve this, we also reccommend in the paper that allometry be tested not jsut again body size but also some other reference trait that is likely to (or been shown to) grow close to isometry. So for example, don’t just measure your dinosaur horn as it related to overall skull size, but also compre it to something like tooth size or humerus lenght. That will help keep things clear when there are other traits around that can grow rapidly or are large but that don’t function as signals. One wonderful example of this we inlcude is a comparisons of the horns on the head of a chameleon with the lenght of the tongue. We used foot size as a reference trait andf show that while both tongues and horns do show allometry, the tongue is little more than isometric but the horns (used in combat and an obvious visual siganl to reflect that) have a much greater allometric slope and show greater variability which is likely to reflect differing quality.

We include a whole raft of such measures of various animals from insects up to mammals and covering both signal and non-signal traits. Two extinct animals were included based on dataset I’ve been working on for a while and may be of interest. One was the frills of Protoceratops which I and colleagues did some time ago but now updated with some extra specimens that we did now have before. These produced a simialr result to our analysis which is no big surprise but nice to see the previous results verified. The second one though was to look at the growth of the tail vane in Rhamphorhynchus.

The standard interpretation of basal pterosaur tail vanes has been that these functioned in steering in flight and acted as something of rudder. That works out quite well since many of the shapes adopted are surprisingly close to the rudders actually made for various aircraft and putting a small vane at the end of the tail would make mechanical sense to increase the effects. However, it is notable that the vanes for Rhamphorhynchus (the only pterosaur where we have a decent sample size) seem to change quite dramatically in shape as they grow and this is rather at odds with the idea that this is purely mechanical. Similarly, there is some serious variation between various basal pterosaurs in vane shape which suggests that the tail is unlikely o be (purely) mechanical in function and the fact that the pterodactloids gfot rid of theirs implies it is hardly critical for flight. Some people have suggested that these vanes were therefor acting as some form of signal and our analysis bears this out. The height of the vane grown very considerably and shows strong positive allometry as the vane changes from a narrow leaf shape in juveniles to a triangle in adults. The vane could of course be multi-functional and it could well be that it has been co-opted from something initially mechanical to function in signaling.

The fundamentals of the methods and theory described here have been around for some time, but the nuance is important to try and distinctuish between traits that are sexually selected and those which are also likely used in some form of display and even combat. It should make for a more reliable way of assessing these kinds of traits and that should be of real benefit to palaeontologists who have an interest in these things. I hope it is not long until more animals are formally assessed for their growth trajectories and what that might mean for understanding their behaviour.

The paper is open access and is freely avaiable here:

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.

Yet more on bite marks

Yes, I have a new paper out and it is another paper describing bite marks on bones. I have done a number of these now and it can easily seem that they are incremental publications with limited application, but this is important stuff. As has been shown across various papers and descriptions, piecing together the taphomonic history of a specimen and the environmental conditions around it, as well as the nature of the bites, is crucial to showing if bites were likely inflicted by feeding predators or scavengers as well as what species/ clades may have left these traces. If palaeontologists are going to be able to amke effective statements about what bites can tell us then it will help enormously if we have numerous detailed datapoints where we are confident about what information they provide.

So, enter a small and beaten up piece of ceratopsian frill. I was shown this a few years ago by Darren Tanke and Caleb Brown after it was found during a dig in Dinosaur Provincial Park in Alberta, Canada. It was unusual in that it was from a fairly young animal and the bite marks were quite small. It is also unusual that these are bites on a frill, it’s not the kind of place an animal would usually feed on becuase there’s bascially no meat there, just a bit of skin and bone which rather points towards these being scavenging traces from an animal that got to a very decayed carcass rather late.

The bites are hard to interpret with lots of cracks and breaks not helping things. There are two clear bites and they fit the classic morphology of theropod traces and we can rule out things like crocodiles, champsosaurs or mammals having been responsible, despite the small size. One looks more like a tyrannosaur bite (though it would have to be from a very small one) and a second looking more like it was from kind of deinonychosaur. It is certainly possible that more than one animal bit this same bit of bone, but equally bite can be variable and identifying them accurately can be very difficult or even impossible to accurately work out who the biting animal was. So despite the apparent possible different candidates it’s hard to say quite what happened here. That’s obviously disappointing, but it’s important to try and evaluate each bite on it’s merits if possible and this does a least provide evidence that even smaller centrosaurs were being bitten by the local theropods and these were not beyond trying to make a snack of a damaged squamosal.

The whole paper is freely available and open access and is online here if you want to see more:

Hone, D.W.E., Tanke, D.H., & Brown, C.M. 2018. Bite marks on the frill of a juvenile Centrosaurus from the Late Cretaceous Dinosaur Provincial Park Formation, Alberta, Canada. Peer J.

 

Non-tyrannosaurs biting like tyrannosaurs

The internet has obviously revolutionised communications between people but it throws up new connections and opportunities that I think few would have seen coming. A couple of years ago, Dan Chure put up a photo on Facebook of a small sauropod femur with some very obvious theropod bites on it. This was from the Dinosaur National Monument site where Dan worked (he’s now retired)  which made it unusual since non-tyrannosaur faunas tend to have far fewer bites in them than do those where the tyrants are present. At first glance though, this looked like a tyrannosaur-type bite with a long set of bite-and-drag marks where the cortex had been really ripped through so this was really unusual. With my extensive background of research on theropod bites, this was something I was very interested in and I didn’t recognise it. I’d assumed something this unusual and interesting would have been described before but not only had it not been (as far as I know it’s not in the literature at all) but no one was even planning to work on it.

So Dan and I got to work on this and inevitably ran into some issues. Identifying what is effectively an isolated and damaged femur from a young animal is tricky. There are a lot of sauropods knocking around in the Morisson and femora are not one of the more diagnostic elements, but we were able to show that it was from a diplodocoid. The femur s under 60 cm long and while that’s obviously a sizeable animal, it is really small for a sauropod and means this was likely a pretty young individual.

The marks on the bone are concentrated on the dorsolateral side of the bone and consist of a series of grooves across the face of the bone that are especially deep at the upper end. At their deepest, these go through the cortex and indeed a fair bit of bone seems to have basically been snapped off, perhaps coming apart as a result of the amount of damage to the element.

This could also have happened at least in part through transport too. Taphonomically the bone has an odd history, apparently isolated, it is actually very close to a second and near identical femur which suggests that both were from a single animal, but there are not other obvious comparable bones nearby and this suggests a very disarticualted carcass. Not only does the other femur lack any bite traces but these are essentially absent in the quarry as a whole. Of the huge number of bones present, only this small saurpod has any bites on it. That’s obviously really rather odd – if loads of carcasses were around, you might expect either tons of bites from theropods getting stuck into the wealth of food or almost none because feeding carnivores avoided biting bones when there was lost of muscle, or they simply couldn’t get to the bodies (if they were say underwater). But one bone badly bitten when even it’s companion wasn’t and then nothing else, is clearly an oddity. It suggests some odd circumstance where this one bone was, perhaps temporarily, accessible to a feeding theropod though the exact details of what may have happened are irrelevant, it does add a level of intrigue to this case.

The bites themselves are reminiscent of those made by tyrannosaurs – long and deep scores made by a bird-like pull back of the head. That action was common among larger theropods but the specialised premaxillary teeth of tyrannosaurs made them well suited to doing this when the teeth were in contact with the bone. Non-tyrannosaurs did not have the inclination to do this when feeding as with their thinner teeth, these would be at risk of breaking. Other fossils show they had the power to bite deep into bones but generally didn’t, rather than couldn’t, making this case a rare example of this behaviour. While it may have been an exception, it does at least show the capacity of non-tyrannosaurs to feed in this way.

Exactly which theropod this may have been though is a still harder question to answer. One of the nice things about bites left by large tyrannosaurs is that they are the only credible candidates for the trace maker in a given environment and you are generally only picking between a couple of pretty closely related species. You may struggle to say if a bite was from Albertosaurus or Daspletosaurus say, but it was still a large tyrannosaur with fundamentally simialr anatomical specialisations and behaviours and therefore general interpretations are going to be pretty solid either way. In the Morrison though you have large allosaurs and ceratosaurs and some unstable / uncertain taxonomy too (like Saurophaganax) meaning the options are much more open.

Various researchers (inlcuding me) have commented on the possibilities of using the spaces between teeth as an indicator of which animal might have left a given mark. However, as Dan and I cover here while in theory that could be useful, in practice we can’t account for the variables of things like ontogeny and missing or offset teeth and the angle at which an animal might drag the head could all dramatically affect the spacing between traces left by the teeth. In short, where there are mutliple credible trace makers it it going to be very hard to pick between them without soemthing diagnostic like shed teeth.

Still, wit no large tyrannosaurs around in the Morrison, whatever did this was not one so we can at least say confidently that at least one large theropod was engaging in tyrannosaur-style feeding, even if it was rare. Perhaps of course the style of feeding was common but merely tooth-bone contact was limited and this fits with waht we do know about that pull feeding action. Even so, this is something of a frustrating project between the quirky history of the bone and its bites and the uncertain identities of the bone and the trace maker. Hopefully more traces like this will turn up or be described from Jurassic beds and we may begin to piece together the feeding styles of large theropods. This one might be a partial mystery for now, but it hopefully provides some useful data fitting into what we know about the behaviour of some of the big theropods other than tyrannosaurs, even if this leads to the idea that they may have been more simialr to each other in this regards than we previously realised.

 

Hone, D.W.E., & Chure, D.J. 2018. Difficulties in assigning trace makers from theropodan bite marks: an example from a young diplodocoid sauropod. Lethaia.

Ceratopsian horns and frills – what drove their evolution?

So I have another new paper out on sexual selection and what this means for dinosaurs. This one has been led by my PhD student Andy Knapp (follow him on Twitter here) and he agreed to write about it here:

Ceratopsians are among the most instantly recognisable dinosaurs thanks to their enormous, elaborately-adorned skulls. The frills and horns of ceratopsians have been the subject or ongoing debate in palaeontological circles since the discovery of Triceratops in the late 19^th century. Triceratops is known to everyone, specialists and non-specialists alike, and remains the classic example of ceratopsian skull morphology, with three large forward-pointing horns and a thick, shield-like frill extending back from the rear of the skull. It seemed obvious to early palaeontologists that these features had evolved for protection. The trouble is that Triceratops is almost alone in possessing this precise combination of features. Many of the larger ceratopsians that we know of didn’t have such large horns, and most had large, weight-saving fenestrae in their frills which would offer little protective value in life. In recent years the large number of known ceratopsian species has increased with a steady stream of new discoveries, each with its own characteristic horn and frill morphologies. These discoveries have posed a whole load of new questions as to what their purpose was.

Large, elaborate features with no obvious use – such as the frills and horns seen in ceratopsians – are expensive to grow and maintain, and obvious parallels in living creatures involve sexually selected features. The most extravagant examples of sexually selected features, as realised by Darwin in his book The Descent of Man, involve extreme sexually dimorphism in traits and/or overall size; peacock tails, elephant seals, etc. In contrast, there is no convincing evidence of sexual dimorphism in any ceratopsian taxa. This has led some researchers to reject the hypothesis of sexual selection as an explanation for exaggerated features in ceratopsians and other dinosaurs, and suggest that instead these features have evolved for species recognition.

Species recognition is the idea that being able to differentiate members of your own species is vital in herding, protection and mating. Basic examples of ‘species recognition’ are everywhere in nature; zebras don’t have trouble telling lions apart from other zebras! The more specific idea that physical traits evolve as a mechanism to allow differentiation is controversial. There are a few known examples of divergence of traits in closely-related taxa where hybridisation could be detrimental to fitness, a process known as reproductive character displacement. This is distinct from ecological character displacement, where sympatric taxa that fill similar ecological niches diverge in traits associated with resource acquisition. The rock nuthatches Sitta neumayer and S. tephronota exist across central Asia in partially overlapping ranges. Where they are sympatric, the distinctive dark eye stripe, ubiquitous across the rest of the two species’ ranges, fades in intensity in the population of S. neumayer. This has been interpreted as an adaptation to prevent hybridisation between the two species. Crucially, other known examples of reproductive character displacement involve minor modifications to pre-existing, often sexually selected features.

Reproductive character displacement is not expected to operate where a taxon exists in isolation, because there is no evolutionary pressure for traits to diverge. This prediction allows us to test the hypothesis of species recognition as an explanation for the presence of distinctive traits in extinct taxa for which we have good geographical information. Ceratopsians fit these criteria well. They were widespread across North America and Asia, speciose, and many species are known from relatively complete remains. We compiled and assessed a list of 350 cladistic character traits for a 46 well-known ceratopsian species and compared how the traits generally considered ornamental, and thus contenders to be species recognition traits, varied between sympatric and non-sympatric species. We also examined at other traits; those that were internal and therefore not visible during the animal’s life, and those that were external but not considered to function as a display trait. We then conducted a pairwise comparison of each possible species pair for three distinct character classes; internal, display, and external non-display.

We then compared the results for species pairs known to be sympatric and, therefore, likely to encounter one another in life, with non-sympatric species pairs. For each category we found increasing character divergence with increasing phylogenetic distance as expected, but, crucially, found no difference between the disparity of the display characters of sympatric species and those of non-sympatric species. This suggests that interaction between species has no effect on the evolution of ornaments in ceratopsians, and that species recognition is not a contributing factor to ornament evolution. Of course, it is entirely plausible that ceratopsians were able to identify conspecifics by their ornamentation, but this would have been a byproduct of ornamentation, not a cause.

The ruling out of species recognition as a driver of ornament evolution, at least in ceratopsians, shortens the list of possible explanations. Avoiding hybridisation would benefit both parties and so the evolution of distinguishing features should tend towards a zero-cost exercise. In contrast, ceratopsian skulls are the largest of any terrestrial vertebrate and impose certain limitations on their bearers. Computer models of ceratopsians have shown their massive skulls shifted their centre of mass further forwards than other quadrupedal dinosaurs. Compared with the hadrosaurs that they shared the ancient river deltas of what is now Canada’s Dinosaur Provincial Park, this made them poor swimmers and liable to drown when crossing bodies of water. This obvious handicap, along with the sheer cost of growing and maintaining such a large component of overall body mass that has no obvious mechanical or ecological function, points to an explanation that favours investment in high-cost structures.

An additional result of our analysis was that at the lowest phylogenetic distances, ornamental traits were around ten times more diverse than internal traits and three times more diverse than non-ornamental external characters. This suggests a general trend for rapid evolution of ornamental traits. Rapid evolution and high-cost are both hallmarks of sexually selected features. If the frills and horns of ceratopsians are sexually selected, as has been previously suggested, they are distinct from extant taxa in being both highly exaggerated and sexually monomorphic. This combination suggests strong sexual selection that applies more-or-less equally to both sexes. Some evidence for ceratopsian ornamentation being sexually selected has been demonstrated previously, and this study both adds to this evidence and rejects a competing hypothesis. Ultimately, our findings open up further avenues for exploring the life history and ecology of these fascinating and enigmatic creatures.

 

Knapp A, Knell RJ, Farke AA, Loewen MA and Hone DWE (2018). Patterns of divergence in the morphology of ceratopsian dinosaurs: sympatry is not a driver of ornament evolution. Proc. R. Soc. B. 20180312. http://dx.doi.org/10.1098/rspb.2018.0312

 

References

Brown WL and Wilson EO (1956) Character displacement. Systematic Zoology. 5: 49-64

Darwin, C. (1871). The Descent of Man and Selection in Relation to Sex. London, John Murray

Henderson DM (2014). Duck Soup: The floating fates of hadrosaurs and ceratopsians at Dinosaur Provincial Park, in Eberth D and Evans D (eds). Hadrosaurs. Bloomington: Indiana University Press. pp. 459-466

Hone, D.W.E., Wood, D., and Knell, R.J. (2016). Positive allometry for exaggerated structures in the ceratopsian dinosaur Protoceratops andrewsi supports socio-sexual signalling. Palaeontologica Electronica. 19.1.5A: 1-13

Knell RJ, Naish D, Tompkins JL, and Hone DWE (2012). Sexual selection in prehistoric animals: detection and implications. Trends in Ecology and Evolution. 28; 38 – 47

Maidment SCR, Henderson DM, and Barret PM (2014). What drove reversions to quadrupedality in ornithischian dinosaurs? Testing hypotheses using centre of mass modelling. Naturwissenschaften. 101: 989 – 1001

Padian, K. and Horner, J.R. (2010). The evolution of ‘bizarre structures’ in dinosaurs: biomechanics, sexual selection, social selection or species recognition? Journal of Zoology. 283; 3 – 17

Spinosaurs in review (sort of)

So I have a new paper out written with Tom Holtz and looking at the spinosaurs. It covers a number of issues and should have something for everyone working on this group be it taxonomy, behaviour, ecology or anatomy. This is an odd paper for a number of reasons and while I think it came out just fine, it might be worth looking at the background.

It was originally penned to be part of a special volume of papers which then never happened and this lead to major delays between submission and publication and thus while the title harks back to the original description of Spinosaurus, it is now a little dated. It is also odd because it was conceived originally as something close to a chapter from The Dinosauria (2^nd ed) but obviously focused on a much smaller group. That means it’s something of a review of both the history and state of the art of spinosaur research, but was then an opportunity to clear up a few issues and introduced some ideas and corrections and thus while it is a review generally, it also has novel material and corrections. That means it rather awkwardly straddles the boundary between ‘review’ and ‘original paper’ and while it leans more to the former than the latter, it’s certainly got elements of both.

The spinosaurs have had a real renaissance of attention in recent years. Leaving aside the huge interest (positive and negative) surrounding the new Spinosaurus material there have been a bunch of new taxa named recently (Ostafrikasaurus, Oxalaia Ichthyovenator) as well as revisions of others (Sigilmassasaurus) and plenty of new finds like sets of teeth and cranial remains of even well-known taxa. In short, we’ve never had more material to work from but in many ways we’re hampered. Major taxa still await decent descriptions and many taxa, while valid, are based on limited material. That makes comparisons difficult and hampers research.

One area where we hope we have made a real contribution was in tweaking various taxonomic definitions. Baryonyx is a real case in point as its definition has not really been revised for some time and numerous characters that were once considered unique to the genus are now known to be present in many other spinosaurs and thus are not diagnostic to this animal. That really means little more than a bit of housekeeping in terms of sorting out some character states but it needs doing and (hopefully) we have now cleared up a few issues with the various diagnoses.

The other area we take a look at in more detail is some of the hypotheses about the behavioural ecology of the group. There have been lots of hypotheses about how these animals lived, and especially the function of the jaws, claws and sail. Many of these are mutually contradictory and the supporting evidence and arguments greatly limited or frankly non-existent. We try to critically appraise a few of them and put things on a firmer footing, but we do also note that spinosaurs may have been decent diggers.

There are whole suites of characteristics seen on animals that are good at digging and these are seen in some dinosaurs not least the alvarezsaurs. The spinosaurs and not anything like this specialised but do show at least a couple of these traits (the large claws and robust humerus for example) suggesting this is a hypothesis worth of some consideration in the future.

I’ll leave it there as obviously the real place to read all of this is in the paper which is online here. Good reading!

Hone, D.W.E., & Holtz, T.R. 2017. A century of spinosaurs – a review and revision of the Spinosauridae with comments on their ecology. Acta Geological Sinica.

Buried Treasure – Matt Wedel

I’m not quite sure whether I’m supposed to be talking about my favorite paper out of my little flock, or the one that I wish had gotten more attention. But it’s okay, because the answer in both cases is the same: my 2012 paper on long nerves in sauropod dinosaurs. It’s freely online through Acta Palaeontologica Polonica.

This one is my favorite for several reasons. I think it’s the most personal of my papers, in that there was no obvious need for it, and probably no-one else was ever going to write it. Whereas with pneumaticity I just got in at the right time – that work was going to be done by someone, and probably sooner rather than later. I also like the long nerve paper because all it required was thinking. I didn’t discover anything, and I didn’t do any real work. In fact, at the outset I was basically thinking of it as sort of a stunt paper. If it had any broader meaning at first, it was merely, “Ha ha, I thought of this before anyone else did.”

But that’s the great thing about science – if you pick up any given thread and follow it, you may soon find yourself in a labyrinth of possibilities, like Theseus and Ariadne in reverse. That happened with the sauropod nerve project, which has spun off in a couple of new directions for me. One is thinking more about the peripheral nervous systems of extinct animals, which has attracted almost zero attention so far. It’s pretty esoteric – nerves leave even less of a trace on the skeleton than air sacs – but there are some interesting and useful inferences that we can draw (to find out what those are, wait for the paper!). The second spin-off is that writing the 2012 paper fired my interest in the physiology of neurons, and in fact kicked off some conversations and potential collaborations with neuroscientists. That is a career wrinkle I never anticipated.

Still, I have to admit that it is a paper without a lot of obvious applications. It hasn’t been cited much – about half as many times as other papers of mine from around that time – but I have been happy to see it cited in a variety of fields, including neuroscience, computer science, and linguistics. That’s satisfying because I cited works from a variety fields in writing the paper in the first place. In part that was because cell biology in giant dinosaurs is an inherently cross-disciplinary problem, and in part because the example of the recurrent laryngeal nerve in the giraffe has become widely known and referenced across so many fields.

My goal now is to build on the 2012 paper with at least a couple of follow-ups to show paleontologists that, yes, there is some actual science to be done here, beyond the gee-whiz aspects. That was the subject of my talk at SVPCA last year. And as I said at the end of that talk, if you’re interested in the interplay of evolutionary novelty and developmental constraint across multiple levels of biological organization, thinking about the cell physiology and comparative anatomy of large animals is a fertile playground.