Combat and cannibalism in tyrannosaurs

In recent years, it has become clear that at least some large theropods (and notably tyrannosaurs) engaged in some form of intraspecific conflict that can be identified by the numerous injuries inflicted on various skulls. Unlike predation attempts which would expect to strike to areas like the hindlimbs and tail, these are very localised to the face and imply animals stood head-to-head or side-by-side while doing this. Furthermore, at least a couple of records suggest cannibalism of conspecifics and this too has been seen in tyrannosaurs. Wading in myself, I have new paper out with Darren Tanke which describes a series of injuries to what is a fairly battered Daspeltosaurus skull that gives support to both of these areas, since it has both pre- and post-mortem bites on it from other tyrannosaurs.

First off, I must thank a number of people for getting this research to happen at all. The project started while I was unemployed and obviously short of research funding. My trip to Canada to examine the material was supported by a crowd-sourced campaign run through Experiment.com. Numerous people at Experiment and huge numbers of friends and colleagues contributed (and I’m sure, plenty of regular Musings readers) and they need my thanks. First among equals was the palaeoart community with Julius Csotonyi, Luis Rey and especially Brett Booth donating artwork or sales to support the work, but many people are gratefully acknowledged. Don Henderson put me up while I was in Canada, and Darren Tanke obviously invited me to write up the specimen. While naturally a lot of work has gone into this paper, the essentials of the marks and interpretations were things Darren himself had identified years ago so much credit needs to go his way there too.

Right, onto the paper. It’s freely available through PeerJ and with 17 figures, so there should be more than enough info there for those who want to delve into the details, and thus I’ll try to keep things relatively brief here. The specimen is of something close to a sub-adult animal and there were plenty of the bones in the quarry (importantly these are in superb condition and there’s basically no evidence of transport or wear). There are numerous injuries across the skull (though absent elsewhere) and these consist primarily of healed injuries on the cranium. Not all of these can be directly attributed to bites, and some could have come from a number of sources.

However, a few healed marks can be interpreted as bites. There are some circular marks and punctures on various locations (including on the snout) and damage to bones that appear to represent some heavy impacts (deviated bones, pieces that have broken off and then fused back to the bone slightly out of position) and the like. Quite incredibly, both sides of the occipital region show some serious damage. On the left a piece appears to have been entirely removed (there’s healing round the remaining edge) and on the right, there’s a healed but circular puncture through the bone. In short, at least one and probably two separate bites came in to the back of the skull and snapped through the bones, though the animal survived and the injuries healed.

This animal, despite not even having reached adulthood, clearly got into at least one big dustup and I would imagine, probably several, to have got so many hits to the head. Although there are a number of theropods showing injuries to the head that are interpreted as coming from other conspecifics, this is more extensive and serious than I’ve seen before. As to assigning it to a conspecific, this is tricky as there are other large tyrannosaurs in the formation (Gorgosaurus) and though these animals might well have come into conflict with one another, one can expect that conspecifics would likely come into contact more often (competition for similar niches, living in more similar habitats or direct interactions from being in groups perhaps). Thus it’s reasonable to infer this was a more likely source of such injuries.

Even so, the post-mortem damage is perhaps more interesting still. There’s one series of score marks along the inside and rear of the right dentary that well match similar bite marks from large theropods. A piece of bone has also broken off between two alveoli and been jammed down in between them and the score marks are coincident with some damage to other parts of the posterior mandible, so it looks a lot like there was a big bite here that took apart the back of the jaw. Given the position of this and the lack of healing, it’s reasonable to infer this as being post-mortem, but things get more interesting when you look at the taphonomy.

When discovered, the dentary was more anterior than would be expected if the specimen had decayed in situ (the skull was lying with the palate uppermost). However, a number of dentary teeth (including those that must have come from the missing right dentary) were lying in the palate below where they should have been if the dentaries were in a natural position. Given the lack of evidence for fluvial action generally, this implies that the jaws were originally in place, decayed sufficiently to shed their teeth, and then the dentaries were moved. One has vanished and the other is in a more anterior position than if the specimen had simply decayed in situ (and the teeth have been dragged along somehow). It’s hard to imagine the tooth ligaments coming apart within hours of death, and the lack of bites to other parts of the specimen that would have been a more obvious target for feeding suggest this was probably scavenging.

This may or may not have been cannibalistic as it is not possible to tell apart Gorgosaurus from Daspletosaurus based on the bite marks alone. Still, it is very much a record of a scavenging interaction between two large tyrannosaurs and that is a nice addition to the available information on interactions between large theropods. Getting an idea of how these kinds of things worked in past environments really is a case of building up data from the rare occasions when such interactions are preserved, so while interesting in its own right, this really does help produce a more rounded picture of interactions between large carnivores both before and after their deaths.

 

Hone, D.W.E., & Tanke, D.H. 2015. Pre- and postmortem tyrannosaurid bite marks on the remains of Daspletosaurus (Tyrannosaurinae: Theropoda) from Dinosaur Provincial Park, Alberta, Canada. PeerJ, 3 e885.

 

Finally, while I’m talking about crowdfunding stuff, do check out David Orr’s appeal for his kids book on palaeontology. David designed the snazzy logo that I used for this project as modeled by myself and Darren above, so you can see how good his stuff is. Oh yes, and here’s an interview with myself and Darren Tanke on the new paper.

Protoceratops take shelter – new palaeoart

Although PLOS has many things to recommend it, one thing they don’t do is give you a lot of notice about publication and so actually the production of my recent paper on Protoceratops came shortly before the manuscript went online. As a result, although the paper had been around in various guises for several years, it was a bit too short notice to have everything ready for its publication, including both a press release from me and the following artwork.

The superb illustrator Andrey Atuchin had very generously got involved in producing an illustration to come out alongside the paper, but his recent illness coupled with the limited notice put everything back. However, I am delighted that he has now completed his new work and allowed me to put it up here.

Above is a simple (but fantastic) vignette of a single Protoceratops. This represents the age class of the block of four young animals that were the feature of the paper, with the reduced size of the frill and the overall proportions of the animal that does differ from what we see in adult animals. Although juvenile dinosaurs are often rare, there is a natural tendency for only full adults to be illustrated, or we see young animals only in the context of their parents or part of a herd and it’s great to be able to focus on a single animal, especially when the adult is already so familiar.

This then makes the whole composition below rather unusual and of course very fitting for the paper. We see the group of juveniles together, devoid of adult supervision or as part of a herd but in their apparently natural aggregation. The environment of course reflects the Mongolian Late Cretaceous with a very sandy region and little real plant life. The overall composition though hints at the wider issues of the paper in a nicely understated way – the group are largely at rest, though remain vigilant and the fact that there are multiple individuals means even those not directly scanning the environment are not that vulnerable and the group as a whole are looking in multiple directions. Staying vigilant is especially important for young and vulnerable dinosaurs lacking the size, experience and defences of adults, and so they must with here a pair of Velociraptor on the horizon.

My thanks of course to Andrey (who retains the copyright on these, please don’t share without permission) for this wonderful rendition of group living in the Cretaceous and nice of him to sneak some theropods in there so I can forget about my fall from grace and pretend that this is not just about ornithischians. It’s a wonderful piece and it really does convey not just the contents of the paper, but the issues at the heart of it, and even if you disagree with the hypotheses, it’s certainly evocative and really does show the concepts magnificently.

 

 

 

 

Social behaviour in the dinosaurs

So yesterday I looked at the groups of Protoceratops specimens and the inference that at least one population of P. andrewsi tended to form groups throughout ontogeny. I also commented on how this was put in really conservative terms – I carefully avoided using the term ‘social’ and didn’t extrapolate up to other populations, species or genera, let alone entire clades. This is an area I’ve commented on before, but in this paper take a more detailed look at social behaviour and what we can and cannot say about extinct dinosaurs.

The first point to make is about the terms themselves. Look through the literature and discussions of dinosaur behaviour and you will see the term ‘social’ especially thrown around but often without a specific definition or context. Unfortunately this is really unhelpful as, although there is no strict definition out there, it does cover a multitude of different magnitudes of behaviour and seems often to be used to mean little more than ‘in a group’. This really needs cleaning up, and we need to be much more careful and specific – you can find a whole group of grizzly bears together fishing out salmon, but I’d not call them social (if anything they are antisocial the vast majority of the time) and this is a far cry from the social groups formed by say chimps or meerkats which are almost always together and have constant interactions. A group of dinosaurs together does not inherently mean some form of social group with say hierarchies, social bonding, shared responsibilities etc. and could be a simple as asocial animals coming together to breed, migrate, avoid some natural disaster or other effect. Separating out say truly eusocial animals like molerats from bears or some crocs which will tolerate each other under some circumstances is going to be hard given the limitations of the fossil record, and is probably impossible most of the time.

On top of that, individuals can form groups for part of their lives, switch between solitary and group living at different stages (ontogenetic or annual), and can be wildly different between populations of a single species, let alone other members of the genus or family. Groups can be all male, all female, equal ratios, harems, mixed adults and juveniles, or all of single cohorts. The net result of course is that conservatism I mentioned before. Taking a trackway or a mass mortality event or set of nests and saying “hadrosaurs were social” is a terrible idea, and I think most of the time the best we can and should say is “this species has some gregarious tendencies”.

Now I should make clear two things. First off, I don’t think that this means we have no evidence for sociality in dinosaurs or that many were not social, merely that (as with a great many behaviours) the evidence is profoundly limited in the fossil record. Given how diverse dinosaurs were and the sheer number of mass mortality sites etc. many species I am sure were social or at least tended to aggregate into groups, but picking an individual genus and saying “this is the social one” based off one or two mass mortalities that probably span different species, times, places etc. is probably a poor inference. Secondly I also think we can make good inferences for some species – multiple mortalities that are from different seasons, evidence of strong social interactions like display structures or intraspecific combat, inferences from other very close relatives showing similar patterns can probably build up to make a pretty strong pattern, but this would still not rule out some individuals being solitary or complex switches between different systems.

So, if we are at least seeing some degree of gregariousness within some populations (and as before, I think we can make a decent case for Protoceratops) why might this be happening? Another interesting aspect of this is that when we do have mass mortalities of dinosaurs they are very often exclusively of juveniles. Given how rare juvies are generally, it should be a bit odd that a rare event of a mass mortality should trap juveniles. There are adult only groups and mixed groups for various dinosaurs, but there are plenty that are of only subadults, or younger animals, and these may have multiple mixed age groups, while still all being juveniles.

Now both juveniles and adults would come together for some reasons like feeding, migration, natural disasters like drought, or perhaps long-term parental care. We would also expect to see adults come together to breed and nest, but that won’t apply to the little ones, so what effect might drive juveniles together but not adults? One obvious factor is predation. Yes, again this is an area I have heavily trodden before but juveniles of almost all species are much more vulnerable to predators that are mature animals. Adults are better at recognising threats, forage in better areas and for less time, and are typically either faster or better equipped to fend off attacks too.

One thing that can really benefit juveniles however is vigilance. Their long foraging times in poor areas means they are often not spending much time looking out for threats. Hanging around in a group though means that at least someone is generally keeping an eye out, (and as a bonus if you are found, at least the predator may eat the guy next to you, rather than attacking you). Adults may even keep juveniles away from them since as well as competing for food, but actually drawing in predators and so creating danger, so we might expect juvies to bunch up, when the adults may be less fussed. I would expect juvenile ankylosaurs for example to hang around in groups when their armour is little protection against a big tyrannosaur, but the adults might be largely immune and so would not need this effect to help them. Plenty of studies on extant species show that groups form, or increase in size, when there are more predators around and so this would fit the patterns we see here – juveniles are likely to stick together at times when adults may not because they want to avoid being eaten.

So overall we suggest that juveniles of dinosaurs might have formed aggregations, (and in some species where the adults were largely solitary) as a defence against predation (or at least as a major driver of it) but that this does not necessarily imply strong social interactions, merely the formation of groups. We need to separate out much more carefully what we mean by the term ‘social’ and start being much more specific about what that word means and degrees of social interactions, group formation, gregariousness and the like. Conflating multiple different terms (or leaving them so broad and undefined as to cover almost anything) does no one any favours – we can’t compare and contrast different specimens or make meaningful statement about what they might have been doing. We can call migration, group hunting, group formation, nesting together, and parental care social behaviours if we want to, but it’s worth separating them out and we need to do just that if we want to have meaningful discussions about what these animals did and did not do.

 

 

A block of baby Protoceratops

My new paper is out today and it describes a wonderful new specimen of four baby Protoceratops together in a single block. Unlike many other groups of exceptionally preserved specimens from the Mongolian Gobi, the animals are effectively stacked on top of one another and all facing in different directions and importantly, their inferred age is different to other Proto specimens.

This specimen was actually collected in the early 1990s, something I hadn’t realised when I saw it in 2011 in the Hayashibara museum in Japan. This was my second trip to the museum after having been in 2009 (that led to the Tarbosaurus bite marks paper) and this was the specimen that really grabbed me and I am obviously most grateful to co-author Mahito Watabe for allowing me to lead the paper on this.

The preservation is superb, and although there’s been some erosion and damage (especially to the uppermost animal) at least one of them is brilliantly exposed and almost immaculate in condition. At this point I must praise the preparator for his incredible work here, this is a huge block (close to a metre cubed), the matrix is exceptionally soft and brittle and the organisation of the specimens must have made the whole process extremely difficult and the result is both beautiful and impressive.

There are two major aspects to the paper (which is in PLOS ONE so for all the details and tons of pics so you can read it all there) and I’ll deal with them in separate posts. The first one is the block itself and the implications for Protoceratops generally. There are a number of groups of this dinosaur known already – several sets of adults, a pair of subadults (also briefly covered in the paper – and shown below) and a set of very young animals that were described a few years ago as something close to hatchlings in a nest. In the paper we actually suggest that these were not in a nest, but free living, but the wider point is that we have similar sized animals (that are probably of a similar or the same cohort) together at multiple different life stages, and we don’t seem to see mixed cohorts as with many other dinosaurs.

The block here slots into this pattern beautifully, the animals are about twice the length of the smallest ones, and about half the size of the subadults. That means we can put together a sequence of specimens at four pretty distinct life stages where we have groups of animals together at different times of their lives. That is something we have not been able to do for any extinct dinosaurs before – we do often have groups together and often of adults or juveniles or the two mixed together, but we are not aware of a so many obviously different cohorts of a single species showing this. Wonderfully, these are not all just Protoceratops, but all P. andrewsi and even better all of these are from a relatively narrow time and space window.

As non-avian dinosaurs go, that’s about as close to a single population as you are really going to be able to find, so collectively we are inferring that this was a pretty normal behaviour for this population. That sounds like a pretty conservative approach (can we not apply it to the genus or species as a whole?), but I think it’s something we really need to do a lot more of in palaeontology. The sheer variety and plasticity of many behaviours, especially when it comes to forming groups, means that is probably dangerous to extrapolate without some good supporting evidence and that sets things up quite nicely for the second post which will follow tomorrow.

Project Daspletosaurus 2013

I’m sure a goodly number of readers are already aware of this as I’ve been tweeting and facebooking it quite a lot, but I have a science kick-starter project running on the Microryza site. It sounds almost too contrived to be honest, but it’s a project aimed at looking at possible cannibalism in Daspletosaurus based on material Darren Tanke has worked on at the Tyrrell.

Obviously Darren and I have form when it come to tyrannosaurs, both with our own research interests and in particular with the Gorgosaurus preparation project. Here though it’s a skull of Daspletosaurus with bite marks attributable from another large tyrannosaurine. I’m looking for funding to get me out to Alberta and check out this and related material and work to write this all up and hopefully learn something about tyrannosaur behaviour and ecology.

I’ll skimp on the details here because it’s all up on the Microryza site, so do follow this link and take a look. More specifically, if you can spare a small amount towards the total, it would be very much appreciated and do please blog and tweet this – the model only really works if people know about it and are intrigued or excited so spreading the wrod is very important (and free!). Obviously I’ll be blogging the project and putting as much information out as I am able, so I hope to make this as open as I can and get the audience involved.

My thanks to Microryza for supporting this, and to David Orr for the fantastic logo up top and Matt van Rooijen for help with the project video (featuring much Matt artwork).

 

 

Fighting zebras

On my recent trip to Marwell, I and my colleagues were treated to quite a number of interesting animal behaviours. One of these was a pair of zebras having quite a serious disagreement. The encounter lasted a good few minutes and with lots of kicking, biting and general jostling. All of us burned off plenty of frames on the cameras and we come out with some good shots, and here are the best of mine.

As usual though, there’s a little scope for me to mention dinosaurs and palaeobehaviour. While obviously some animals were better equipped than others to fight, pretty much all species engage in some form of intraspecific combat at some point. You don’t have to have horns or tusks or spikes to inflict some serious injuries on your opponent and while a zebra may be rather less well equipped to deal out damage than say a buffalo, that doesn’t mean it can’t injure or kill another zebra. Similarly, while I imagine the primary reaction of any hadrosaur to a serious predator would be to flee, I’m sure that a pair of edmontosaurs with enough to fight over would have bitten and stomped as far as possible and fights would doubtless have got nasty – it wouldn’t just be the ceratopsians that would have tried to defeat one another.

Incidentally, I can’t help suspect that ‘the fighting zebras’ is the name of some US college basketball team or some long forgotten infantry company. And if it isn’t, it really should be.

Velociraptor scavenging an azhdarchid pterosaur

Image courtesy of, and copyright to Brett Booth.

So yesterday at short notice I rushed up this teaser post which seemed to do the trick, and now I’ve got a bit more time on my hands, I can start putting down a proper post on the subject. Yep, I have a new paper out and this time featuring dromaeosaurs and pterosaurs. Long time readers will remember that almost exactly 2 years ago I had another paper out on dromaeosaur scavenging featuring shed teeth and bite marks on some Protoceratops material. Coupled with the famous fighting dinosaurs specimen we have pretty good evidence for dromaeosaurs, and specifically Velociraptor for feeding on this dinosaur. The record of dromaeosaur predation and feeding is actually pretty good compared to other theropods groups and there is also an isolated pterosaur wing bone from Canada with shed dromaeosaur teeth and bite marks.

This ‘new’ specimen marks the first record of gut contents for Velociraptor and the first record of a pterosaur bone as gut content in a theropod. (The ‘new’ is becuase this specimen was actually found in the 1990s, but has yet to be described, though I’m told there’s a photo of it in Luis Chiappe’s recent birds book). Thus we do have rather exceptional evidence for a Velociraptor chowing down on an azhdarchid.

Velociraptor specimen with a pterosaur bone as gut content (black arrows). From Hone et al., 2012

And here it is, well part of it. The Velociraptor in question was remarkably well preserved and complete which allowed the preparation of it with the chest cavity as a single articulated piece with the vertebrae, sternum, ribs, gastralia and even uncinate processes all intact and in their original positions. The bones are really well preserved and much of the material has been prepared free of the matrix entirely. One obviously example is the skull which, bizarrely, is on display in Barcelona so at least some reader might have already seen that, though sadly I haven’t and had to rely on some superb photos kindly sent by Fabio Dalla Vecchia. It’s hard to show the bone off properly what with the whole ribcage in the way (which is, incidentally, a broken ribcage, one of the ribs took a huge battering and shows a healed break – white arrow in the above picture). S you’ll be delighted to know there are also some close-ups in the paper like this one (below) and even some CT scans in the supplementary data.

Close up of the bone. From Hone et al., 2012

As you can see the bone is incredibly thin-walled which is the major reason that it’s inferred to be an azhdarcid pterosaur, though their presence in the Late Cretaceous, including a related formation, and the general absence of other pterosaurs in the Late Cretaceous helps support this identity. Given what is around and the thinness of the bones, it’s pretty unambiguous as indeed is the identification of the dromaeosaur as Velociraptor given that we have basically the whole thing. In short, this is about as convincing a case as one could make that a Velociraptor had eaten an azhdarhid. But was it really scavenging? Well that and other issues I’ll be talking about tomorrow, as there’s quite a lot more to say on this. Stay tuned.

Finally, my thanks to Brett Booth for more awesome artwork for me to use, and you can see more of this and my interview with him on his dinosaurs here.

Hone, D.W.E., Tsuhiji, T., Watabe, M. & Tsogbataar, K. Pterosaurs as a food source for small dromaeosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology, in press. Horrible uncorrect proof and behind a paywall, but the abstract, figures and other bits are visible to all.

Triceratops vs Tyrannosaurus

Perhaps the most obvious mainstay of dinosaurs in art and culture is the stand-off between the giant, fanged Tyrannosaurs and the horned and frilled Triceratops. It’s pretty much a cliché for dinosaurs that these two will fight each other when together and that the predator is always after his well-defended prey.

Obviously, I generally don’t think that tyrannosaurs (or most theropods for that matter) tackled healthy adult prey when there was a great selection of tasty, small, largely defenseless and naïve juveniles around. Now that makes sense at the best of times (and is borne out by what modern predators do, not to mention the inferences about dinosaurs) but a photo like this really makes you wonder.

OK, rexy is lying down (and it’s not the biggest specimen), but the difference in size is quite obvious. Triceratops is really, really big. Even in comparison to the ‘king’ it’s a huge animal with a massive skull, long horns, and a big body and a lot of weight behind it. There’s reason lions don’t generally tackle adult buffalo and won’t go near rhinos and that’s because they are too likely to get stompted, gored, or generally injured. This is a big and intimidating animal, and while eyeballing skeletons is not the best way of assessing complex behaviours, I do find it hard to believe that this was a normal prey choice for a tyrannosaur.

Marabou stork couchant

 

A trip to Beijing inevitably means a trip to the zoo given that it is opposite the IVPP and costs only a couple of dollars to get in. This time I was on a mission with Corwin Sullivan to look at a variety of birds for some anatomical and behavioural things we are interested in. One thing that did stand out by not standing up was the marabou storks. These are normally quite happy to stand as most wading a long-legged birds do – one one of both legs with the neck rather hunched up to the body (standing marabou above, obviously). However, three of them had adopted a sitting position on the ground far more like a chicken or duck than anything else.

Colour me ignorant, but I’ve never seen this in a bird of this size or this kind and while I can imagine them doing it on a nest perhaps they really seemed to just be resting. Is this common and I’ve simply missed it, or is this genuinely a bit odd?

 

Multifunctionality

I have complained before (who? me? complain?) about the common journalistic fallacy that proof of X is not proof against Y. All proving X does is show that X is true, not that Y is false. However, it’s easy to see how this comes about – many ‘obvious’ anatomical features certain seem to have, or are famous for having, just a single function. Deer fight with their antlers, peacocks display with their tails and so on. However, even some supposedly monofunctional features can have more functions, if more minor ones – the antlers of deer and horns over various bovids are used for fighting off predators as well as rivals, but also act as rather minor heat-loss features. Sure, it’s pretty minor, but it is a function that they perform, and may even be selected for.

Some features however can have a great many functions and all of them may be important. Both the tusks and trunk of an elephant can be used for all manner of things – fighting, signalling, collecting food, manipulating the environment and others. It’s not only hard to say which of these is the most important now, but which (if any) may have been the original driving force behind it’s selection is very hard to tease out. Thus making explicit statements about other functions and the selection pressures behind them is a very risky thing to be do without good evidence. Sorting this out properly requires, as far as possible, testing individual hypotheses about function in isolation and rejecting or accepting them based on the available data.

This should be quite obvious, and yet inevitably in the media (and sadly, on quite a few occasions in the literature) this simple error is repeated. Single functions are tested and found to be a use of a feature but then this is then incorrectly extended to be assumed to be the sole or primary function. Watch out for these, they can be very misleading and it is an exceptionally easy trap to fall into.

Thanks to Rachel Kilby for the photo.

Extrapolating behaviours – picking the right analogue

Palaeobehaviour is perhaps the hardest area of research in palaeontology, and is certainly one with the most speculation involved. If you know where and how to look, there are all kinds of evidence available in the ichnological and osteological record but of course the real issue is interpreting it correctly and tying the evidence to the right taxon in the right way. Sure you have a nice hadrosaur femur with some tooth marks, but from what? A theropod or a crocodile? And did it kill it, or just find it already dead? Was there only one animal feeding or more? Even with a good fossil record to let you know what other animals were out there, and how many, and what the environment was like, there are generally so many possibilities it can be very hard to make even vaguely reasonable generalisations about behaviour based on a single specimen or even a good collection.

Pachycephalosaur head butting

Despite my interests in dinosaur behaviour I have rather managed to avoid the question of pachycephalosaurs so far and with a couple of nice photos on cue it seemed a good time to discuss this at least superficially. I don’t think this clade has actually even been mentioned here at any point so this is longer overdue.

Since I try to cover even the basics of archosaur palaeontology on here I should probably give a bit of background to these bone heads (as they are occasionally know – the literal translation of the name being thick headed reptiles). Pachycephalosaurs are a group of ornithischian dinosaurs closely allied to the ceratopsians (the horned dinosaurs) and with them make up the large and important clade the Marginocephalae. They were herbivorous bipeds that only spanned a relatively small range of sizes from small to medium (compared to many of their relatives) with the largest genus, Pachycephalosaurus, being up to around 5 m long.

Obviously their most prominent characteristic is the massively thickened skull roof and the occasional fringe of spines and knobs that run around the crown of the skull. What these were actually used for has long been contested with the most obvious suggestion being that these were used to fight with, either with each other or to attack other animals (like predators). Evidence has gone backwards and forwards over this with papers saying the head could not have absorbed impacts of fighting, or could have done, that they would clash heads or would not and would target flanks and that these were ornamental or not. In short, the only real consensus is that there is no real consensus as yet.

This may come as a surprise as despite the obvious controversial nature of many questions in palaeontology many are at least close to a consensus or the evidence has started to tip decisively but here this is not really the case. Part of the problem is likely to be the sparsity of material – pachycephalosaurs are not known from many good specimens at all (half a dozen are known from only skulls, partial skulls, or just the domes) and some aspects of their anatomy are thus not well understood. Combined with the relative lack of interest in this clade (since almost everyone seems to prefer theropods) it is perhaps less of a surprise.

The lack of material in Europe especially and the fact that the group is not half as well known as the ‘classics’ like tyrannosaurs and ceratopsians, and their relative small size means that they rarely make it into dinosaur halls outside North America so I was pleased to see two different displays of them in Japan – the first time I’d actually seen any. At the top we have a butting pair from Tokyo and below the front/side and back of a skull from Fukui (both images used with permission). I hope more research goes into this area as it is genuinely fascinating and covers various aspects of mechanics, ecology and behaviour that integrate well and of course the application of data and studies from living animals would be especially useful.

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