Archive for the 'Dinosaurs' Category

Discovering dinosaurs in the field

I’ve already written a bit about the fieldtrip to Alberta from this Autumn that I led from Queen Mary with a team of colleagues and undergraduates where we had a great time and found some great stuff. My friend and colleague Rob Knell was with us as pseudo-official photographer and he also had video capacity with his cameras so took plenty of footage and has now edited this together to make a brief video to show off what we did. This has been put together in order to  promote the course and show future students what the trip is likely to involve, but it should be of general interest to those who have not seen Dinosaur Provincial Park firsthand and what a better idea about hunting dinosaurs.

 

 

 

 

 

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

C skull IIMy 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.

Block view upper front 10cm

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.

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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.

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A population of Shantungosaurus, the largest ornithischian

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Sadly I have to report that after many years working on various diapsids and having published plenty of papers on dinosaurs generally and theropods specifically, and yes even sauropods, I’ve gone and published two papers on ornithischians. I hang my head in shame, obviously, and I hope too many readers won’t think too little of me (though I doubt Tom Holtz will ever return my calls now). The first is on the wonderful Protoceratops and delves deep into dinosaur behaviour (and should be out on Wednesday), but this time it’s the monstrous hadrosaur Shantungosaurus, which has not really had anything like enough attention given just how much material is floating around.

The paper is a chapter in the new ‘Hadrosaurs’ volume that has been long in the making (and indeed publishing, since it as basically done a year ago) and if at this point effectively out. Actually I’m not sure quite how available things are, but the volume has appeared on Google Books (with the incorrect date of 2015 on it) and copies are apparently in mail, plus at least some coverage of various chapters is already out. As a result, I don’t think I’m jumping any particular embargo. though I appreciate not everyone may be able to read it in the next few days. Anyway, onto colossal hadrosaurs.

After the initial excavations of the 1960s, not much happened in the quarries where the remains of Shantungosaurus were first found. It was identified as a giant hadrosaur, plenty of isolated remains were collected and distributed to various collections and then, well, not much. The new digs over the last decade or so have seen a raft of new finds, but all the attention has really been on the other things coming out of the quarries, namely the new tyrannosaurs, ceratopsians and other beasties. That’s a shame as there are literally thousands of elements available to study and these are coming out in multiple quarries.

Over several visits, my good friend and longtime collaborator Corwin Sullivan and I went over the largest of the three main sites at Zhucheng, the Kugou Quarry, and took note of every bone that we could find and identify. The quarry maxes out at some 300 by 30 m, so it’s truly giant, and both ends are missing thanks to the erosion of the hill and it’s not clear how deep it might be. We also could not access every part of it safely and thus although we noted some 3000 elements, we estimate there are closer to 5000 exposed, and there could be huge numbers still to find. Out of these, barely a handful belonged to anything other than Shantungosaurus – a tyrannosaur tooth, a couple of tyrannosaur bones, a croc osteoderm and a bit of turtle. (And, oddly the near complete and articulated Zhuchengceratops, though I suspect it is from a different horizon). In short, this entire area and material essentially represents just one genus and probably a single aggregation.

All the material is essentially disarticulated and while basically every part of the skeleton is there, it is horribly jumbled. There’s no evidence of scavenging or trampling, and little sorting either, so this looks like a pretty major event that led to a rapid burial of the remains. We don’t dwell on what might have done this, but bearing in mind the size of these animals and how many there were and this is clearly something big, and also probably quick (this is not a long term accumulation of material).

Already 5000 elements is quite a bit, but the bones are also big. Shantungosaurus is well known as being a really large hadrosaur, but more than that, it’s absolutely colossal. While femur length is not the best size proxy out there, neither is it that bad, and was the only thing we could reliably measure for large numbers of the elements preserved that would give a decent size estimate. The largest femur we could accurately measure was 172 cm long – bigger than the largest specimens of Diplodocus and comparable to many big sauropods like Apatosaurus and Antarctosaurus. While they do have very different builds as animals, don’t forget that hadrosaurs were not pneumatic, so it’s quite reasonable that these animals had similar masses to those huge sauropods. Similarly that also means that  perhaps many sauropods were not as heavy as the largest hadrosaurs which does have implications for how we look at things like the reasons sauropods did get so large. Mass estimates that are available or can be calculated for Shantungosaurs are extremely varied and this is perhaps due to it being so much larger than anything else known when it comes to hadrosaurs or even other ornithischians. Is is basically off the charts (few ornithischians have femora that exceed 1 m in length, and the smallest specimens we measured were bigger than this) and it probably needs to be tackled with a specific rigorous analysis to get a good estimate. Still, I’d be very surprised if the larger individuals were under 10 tons, and it is probably the heaviest ornithischian known and by extension, probably the heaviest terrestrial biped, since I didn’t see anything in the available material to suggest it could not walk bipedally.

Femora were also measured as they are large elements that are relatively easy to identify correctly and were in relatively decent condition, and so go some way to determining a minimum number of animals in the quarry. We counted 110 and so there is a minimum of 55 animals here, and I would be stunned if there were not very considerably more than that in reality (or indeed many more femora in there that are simply not exposed). But any measure then, this is a lot of animal – over 50 individuals, the smallest of which had a femur over 1 m long, and many of which were large sauropod sized. Indeed, the distribution of the femora actually tells us something too.

Hone Fig 4The range of sizes seen is actually really narrow: almost 85% of them fall between 135 and 175 cm and aside from three small ones that were little more than a meter, the rest form an almost perfect normal distribution. In short, this looks like a natural population of adult animals and we can infer they are adult both on the general size and the fact that all the elements of things like sacra in the quarry were fully fused. It has been suggested before that hadrosaurs form separate groups and that adults may have aggregated without juveniles, and with juvies and /or subadults forming separate groups, and that fits well with what we see here (and this also fits with the ideas covered in the forthcoming Protoceratops paper).

Collectively then the remains from this quarry do look something close to a natural aggregation, representing a pretty massive accumulation of biomass (over 50 animals and likely closer to 100, and probably over 10 tons each). It’s hard not to think about just what this means for a Mesozoic landscape, even a big Zhuchengtyrannus would be pretty much outclassed by one of these, let alone dozens together, and they would presumably have been able to strip huge swathes of vegetation clear as they foraged. For me at least it’s a nice evocative image, though perhaps not a long lasting one given that something massive rather dismembered and buried them shortly afterwards. Happily for palaeontologists we have now found this graveyard and there’s a massive amount of material available on these massive dinosaurs, and I hope that there is much more to come now that it is becoming available for study.

 

Dinosaur Provincial Park 2014

The Musings has been quiet again in part because I have changed jobs / cities yet again, but also with a general wind-up towards the start of teaching. This is now my third year at Queen Mary, but more importantly for me, I’m finally teaching on a course I have specifically created with a colleague and so can really get to grips with an area that interest me in particular. And so a new course on taxonomy and systematics has come into being and a core part of this is actually a fun hands-on practical, namely hunting down, and then identifying, remains in Dinosaur Provincial Park in Alberta. Yep, for some reason the university trusted me to take a team of undergraduates out into the wilds of Canada and the Tyrrell even sent along a couple of people to help collect what we found (we had an explore, but not collection, permit).

Naturally much of the discovered material was very fragmentary and unsuitable for collection (not least by the Tyrrell’s exacting standards since they are buried in teeth and partial skeletons and don’t care too much about isolated verts or longbones), but this didn’t mean it could not be identified. Picking up key skills in identifying characters that can be used to unite things into groups, or split them off as different is a fundamental basis of taxonomy and key to identifying possible characters for systematic analysis, so it’s an excellent introduction into some practical skills on that side as well as the more obvious aspects fundamental to palaeontology and indeed good science (data collection, archiving data and specimens, access to material etc.).

Even so, there were some great finds. We were supposed to have four days in the field but bad weather restricted this to little more than two (though knowing the weather was coming, we pushed hard with long days to maximise the good ones, so we didn’t loose too much time over all), but we still put a dozen specimens into the Tyrrell collections (both research and teaching) including teeth of dromaeosaurs and troodontids, some ornithomimosaur elements, and best of all a hadrosaur skull. The latter was found eroding out of a cliff and while the lower jaws were going and most of the teeth were out, the rest seems to be in the hillside (with probably a decent bit of postcranium)  and this has been flagged for collection next fieldseason.

As this is the first time we have run this, there were inevitably some teething issues, but I’m delighted to say the feedback from the students has been incredibly positive and they really enjoyed both the fieldwork, the Tyrrell itself and interacting with the academics present on the trip (Musings collaborator Mike Habib also made the trip up and joined us). This is hopefully the first of many future trips as this should be an annual component of the course, so hopefully for me, I’ll have a nice source of material for future posts every year. Meantime, here’s some views, the hadro skull, some tyrannosaur teeth and turtle plastron.

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My thanks to all on both sides of the student / staff divide for all their efforts in making this such a great trip for all concerned and I’m really looking forwards to the future of this course.

Welcoming Zhanghenglong

It has been a while coming on the Musings, but here’s something that’s bordering on traditional palaeontology. However, it is based on ornithischians, so obviously doesn’t quite count. That is a joke before I start getting all the complaints in the comments – I’m genuinely pleased to finally be on a paper that focuses on the other side of the Dinosauria after all my saurischian work. Anyway, long term readers will remember this post from back in 2011 about creating plaster jackets in the field. This was from a trip down in Henan were we turned up a number of specimens (and interestingly, Xu Xing was called away up to Zhucheng becuase of the discovery of what would turn out be Zhuchengtyrannus). At the time we had something that looked like a hadrosaur of some sort, and the blocks you can see us removing in the other post form the core of the new paper.

So say hello to Zhanghenglong, a basal hadrosauroid from the Late Cretaceous. Somewhat inevitably there’s not much of it, though there is a good maxilla (shown below) and dentary, as well as dorsal vertebrae, ribs, a scapula and a tibia. Phylogenetically it comes out as a hadrosauroid, but very close to the base of Hadrosauridae and gives some additional support to the idea of an Asian origin for hadrosaur groups with the nearest relatives to hadrosaurs being from Asia, as are the earliest lambeosaurines at at least a couple of members of the hadrosaurines. Happily the full paper is at PLoS ONE so all the information is fully accessible if you want more.

 

Xing H, Wang D, Han F, Sullivan C, Ma Q, et al. (2014) A New Basal Hadrosauroid Dinosaur (Dinosauria: Ornithopoda) with Transitional Features from the Late Cretaceous of Henan Province, China. PLoS ONE 9(6): e98821. doi:10.1371/journal.pone.0098821

Sciurumimus again

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Last week I took a very brief trip to Germany to do a round of several museums and collect some data for various projects I am working on. As well as catching up with some old friends (human and fossil) I got to see some new ones (human and fossil). I’ve been filling in the pterosaurs over on Pterosaur.net (including this guy which is an absolute must-see) but here I thought it would be best to bring back Sciurumimus. This little theropod did make an appearance on here when first described, but now I have a couple of pictures of my own (the specimen is currently on display in the Solnhofen Museum) it seemed time to bring it back. So here’s a couple of additional images of this outstanding little theropod.

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More on the 11th Archaeopteryx

DSCF9843Continuing my collection / database of Archaeopteryx images, it’s time to increase it a little further. Last week I helped out at the Natural History Museum’s ‘open evening’ called “Science Uncovered”. I was there basically to be a scientist for people to talk to, but there were whole stands from other universities with research connected to the NHM and of course a raft of curators, researchers and other staff bringing the behind-the-scences stuff to the front of house. One special had been laid on that really drew the crowds – the 11th Archaeopteryx specimen.

Although it has appeared on here before, this is the first time I had seen it and was able to take some notes of features and indeed get a few photos. The lighting was absolutely nightmarish, but between tons of photos and a bit of tweaking of balance levels I have produced at least a few that are not too terrible, though at not very high resolution and mostly taken at a pretty low angle. Enjoy (as far as you can).

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Species recognition in dinosaurs? Not so much

Those with an interest in dinosaur cranial crests and exaggerated structures (which should really be everyone since they turn up in pretty much every major lineage one way or the other) will probably be aware of the exchanges going on in the literature over these features. Although myself and colleagues have been advocating that sexual selection (and or socio-sexual signaling: the two can be hard to separate) is a likely strong candidate as the prime driver for many of these features, others have been advocating that this is not the case and instead the answer lies in species recognition. The latest to delve into this area is a paper I’ve done with Darren Naish and is the first time we’ve addressed this issue directly. While we have written or contributed to a number of efforts looking at support for sexual selection in dinosaurs, this is the first time we have tackled the other side of the problem.

The paper originally started as a long section that was included in our paper on mutual sexual selection with Innes Cuthill, but as we were later forced to cut down the length of the submission, this was a section that was relatively easy to prune as tangential to the main issue. However, we felt it needed saying and with new data coming out and the discussion ramping up, we revived and revised the work and it is now out. (Well, it has been in press and available for a while but is now properly out).

This is an important area for discussion – after all, the horns, crests, frills, plates, bosses and the rest (not least feathers) are key features and adaptations in various dinosaur lineages and trying to work out how they might have been used and what this means for evolutionary drivers and patterns is going to be a major issue. It’s hard to really understand stegosaurs or ceratopsians say if you can’t say that much with confidence about their ‘bonus’ features. While obviously each clade, or even each genus / species probably needs to be taken on a case-by-case basis when it comes to detailed analyses, some gross patterns can be seen or at least discussed. In the case of species recognition, is it even an actual ‘thing’ when it comes to exaggerated structures, and if it is, how is it supposed to work. The hypothesis has enjoyed some support in the literature for some unusual dinosaur features so it’s well worth examining.

Species recognition (in the context of exaggerated structures) for those who don’t know, is the idea that individuals of a species use these features to help them recognise cospecifics with to ensure they mate with the right species, or to maintain herd coherence. In short, carry round a key feature and you should be able to make it easier to stay in touch with the right animals and avoid the wrong ones. Various lines have been put forward to support this idea (in general and specifically towards dinosaurs) but we feel that none of them actually stack up and some have some serious problems.

First off is a pretty big issue – to our knowledge there is no evidence of any living species using some form of crest or exaggerated structure for species recognition. Individuals of species do recognise each other (not a big shock) but actually things like antlers or casques don’t seem to form part of the pattern that conspsecifics recognise. This may not be a big shock, after all, you can recognise a species by the overall appearance (size, shape, colour), their smell or specific sounds they make, behaviour, and other features. On top of this, some species are very varied in appearance for the big features (antlers of deer look very different as they grow, and are different between males and females and between juveniles and adults etc.) so relying on one feature is a bad idea at best, and a plastic one an especially bad call.

Plus of course, you often get closely related taxa that are sympatric. Is some big set of horns going to help you correctly identify conspecifics if there are half a dozen similarly-looking species also in the area? Look at things like African antelope and gazelle, or more extreme examples like tyrant flycatchers. We have trouble telling them apart sometimes based on their morphology, yet they seem to have no trouble. If this is so critical to dinosaurs, why to the iguanodonts seem relatively free of crests, but the hadrosaurs go nuts with them? And why are they all so similar in general form between species when they are supposed to help separate them out? Surely they should be divergent, not all similar in appearance. And why do we see things like Wuerhosaurus or Spinosaurus running around with all this weight to make sure they don’t mate with the wrong species when there are no other members of their clade to get confused with?

In some cases we see both issues coming together. If we look at the various small protoceratopsians of China / Mongolia, we see disagreement between researchers as to how many species (or genera) there may be. What is notable however, is that the characters being used to separate them out don’t typically involve the frill or bosses of the skull, and where they do, may be things that are not externally visible (e.g. the width of the media bar in the frill). In short – if there are multiple species here, the frills are apparently similar enough that we can’t separate them and so are unlikely to be part of the identity concept of the animals. If however, there is only one species present, then we are back to the paradox of a large frill being carried around but with no other species that could confound any signals.

On top of that, is it really worth it? After all, while you do want to stay in touch and make sure you mate with the right species, bolting on a good few kilos of bone to your head, and then the extra muscle to support it, and then lugging that around for your entire life is a lot of effort. When you can probably already identify conspecifics by their colour, patterns, scent and calls (of simply because nothing else like them at all is on the same continent) surely these would experience strong negative selective pressures if they didn’t have any other support.

Furthermore, how would such features ever evolve? If the populations / species were allopatric then we return to the situation of them not having another group to get confused with and crests are unnecessary for recognition. If they were sympatric though, how would this work? Pretty much the definition of a natural biological population is one that is breeding within itself, but here we’d have to have a population diverging because some don’t recognise each other as conspecifics even though we would expect, pretty much by definition, there not to be too much difference in structure shape between them (e.g. a tiny crest vs no crest). Now some animals might prefer each other, but that’s mate choice, not recognition, and there would have to be enough individuals for this to work – one mutant with a crest when no one else has one is not going to start forming a new species, and if there were a bunch of the with the new crest they’d also have to identify each other as different and avoid mating or hanging around with the others. So how would a large feature that’s for correct recognition allow a population to split in this way? To us at least it appears most unlikely to occur at all, let alone repeatedly.

In addition to this, there is rampant hybridization of closely related species in the natural world (and indeed in captivity). Even extravagantly ornamented species like pheasants with numerous adornments and bright colours and patterns hybridise regularly – clearly no matter how extreme the cue, at least some animals regularly have problems with them or are indiscriminate, but either way they are not that effective.

While some data like the apparent rapid growth of structures late in ontogeny has been used to support the idea that they are characteristics involved in socio-sexual signaling, it’s also a problem for the herd coherency part of the model. After all, lots of juvenile dinosaurs are known from aggregations suggesting they spent a lot of time together, even when the adults did not appear to. If these features were key, we’d expect juveniles to have them, and adult perhaps to shun them when they were no longer needed, but instead the opposite is true. In general the herd coherency argument is a bit odd anyway, again you have lots of ways of identifying and keeping in touch with conspecifics and some are clearly better than visual aids. Scent can have a temporal component, and vocalizations can be interactive beyond line of sight (especially useful in forests, or when things are behind you, or you are foraging and looking down etc.). No matter how big they are, visual structures are not always going to be that useful, even if they are unique.

In the increasingly infamous issue of Torosaurus and Triceratops, if these animals are truly conspecific then for a start we are back to the issue of ‘lone’ taxa (I don’t think Leptoceratops is going to be much of an issue here) and the pointlessness of crests where none are needed. On the other hand, this is also potentially a problem for the mate recognition idea. We know that at least some dinosaurs were sexually mature before they were osteologically mature and this could be the case for these animals too. If so, then the alleged transformation between one morph and the other would create confusion – both the Triceratops morph and the Torosaurus morph (or indeed anything in between) would be viable mates.

In short, we really have no clear evidence for species recognition in any living species, and that alone should make it unlikely to have been a key player across dinosaurs for the whole Mesozoic. Such structures would be costly, and yet not necessarily do the job it is supposed to with other signals being cheaper and just as effective, or more effective in many circumstances. It’s not clear why it should be so important for some clades and not other similar forms (iguanodotids vs hadrosaurs for example) and is clearly either redundant for some taxa, or would not actually reduce confusion. Nor is it clear quite how this would evolve in the first place, or why it would be sustained, and hybridization suggests that crests alone would not even prevent incorrect matings. Put this all together and we feel that there really is no good support for the idea of crests and other structures being primarily used in species recognition. They did of course likely have an effect – it would be odd if Stegosaurus or Corythosaurus didn’t use their respective features as part of how they identified one another. But that does not make them the prime, or only, driving force of all these different features in all these different lineages.

There was a fashion in dinosaur palaeo to write off any odd structure as simply sexual selection and leave it there. This was rightly railed against, but what was often criticised was the fact that sexual selection seemed undiagnosable in the fossil record and so the problem was that it was untestable rather than the fact that such throwaway remarks devoid of context or explanation do little for the subject. Now we are in the odd position where rarely you see very similar comments (in terms of their style) about species recognition popping up in the literature about exaggerated structures despite the lack of support for it, and the now (well, we think), strong cases made for sexual selection, or at least it’s assessment. Although previously the case for sexual selection was pretty weak, it is at least an extremely common phenomenon in living taxa and with obvious powerful effects on anatomy and behaviour. Species recognition has not yet even been shown (in relation to exaggerated structures) in any living clade, and while offhand one-line explanations are not the way to go, it seems odd that one has been replaced with the other.

 

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.

Another incredible Gorgosaurus

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Gorgosaurus has had a lot of love on here thanks to the huge series of posts on the preparation of a specimen by Darren Tanke, but also with this recent effort. Despite the awesome quality of those, this one is arguably better. While not complete (almost no tail dang it) and with a little bit of squishing to the skull, this one clearly retains an awful lot of the 3D relationships between bones and it overall rather uncrushed. This is a rarity to say the least and really helps show just how, well, big these things were. As you can see from the images, the animal is really barrel-chested and chunky. Obviously restoring muscles and fat layers etc. is another issue entirely, but I think it’s fair to say that this animal should really not be slim.

Obviously there’s a ton of just beautiful detail here and some lovely nuances (like the interlocking gastralia, the massively retracted left leg, the ilia tight to the neural spines of the sacrum, and the rugosities on the snout). It may not have quite the visual impact of the last one, but there’s really a lot to be gained from this and palaeoartists out there should be (t0 quote a friend of mine) onto this like a starving chihuahua on a pork chop.

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A fifth anniversary tyrant

The next few days are likely to be very busy for me and this weekend I’m off on holiday, so I very much doubt I’ll be blogging on next Monday. This is a bit of a shame as those who occasionally glance at the bottom half of the sidebar on the Musings will realise that it pretty much marks the 5th anniversary of the blog. Of course very longtime readers will know I was going for some months on the old Dinobase site before cranking up this version on wordpress, but this has for most people always been the home of my pronouncements, even if there is also now Pterosaur.net, the Lost Worlds, and various bits on other parts of the web too.

So I’m naturally really rather pleased to have reached this mark, having also not too long past gone over 1.25 million hits and 1250 posts on here. It has, obviously, been a lot of work. While naturally there have been plenty of short posts (even one liners, and those of just a single image) and a fair number of guest pieces, I’ve obviously poured a huge amount of time and effort into this over the years, and I’d like to think it’s made a fair impression on a goodly number of people. Plenty of great dinosaur blogs by interesting and talented researchers seem to have fallen by the wayside, so if nothing else I can claim a fair bit of persistence.

Right, well to ‘celebrate’, here’s some pictures of a Tyrannosaurus mount from the Tyrrell that I was going to post anyway (so hardly the greatest party ever thrown really). Still, it’s hardly an inappropriate thing to include as I have done my share of tyrannosaur work and this is a neat mount. Oddly, I wasn’t too happy with the photos originally, you can’t see too many details, but I rather like the way this looms out of the murk with the animal trailing off into darkness.

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Although the skull looks great from either side, once you get a shot up the nose, it’s rather clear how distorted this is. There’s quite a bit of difference between the two sides and it’s obvious there’s been a fair amount of squishing to the bones to give this rather asymmetric appearance.
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Well, that’s it for now. Not sure if there will be another 5 years, but I’m not planning on stopping just yet and I’ll be annoyed at least if I don’t reach 1500 posts having gone this far, though with my other commitments, it may take a good long while yet.

Elaphrosaurus

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Elaphrosaurus last got a mention here way back in 2009 when Limusaurus came out. In the phylogeny accompanying that paper, the two were recovered as sister taxa which hinted at the possibility that Elaphrosaurus was also herbivorous. Given that there’s no known skull, that’s not as outrageous as it sounds alongside this image – the head was reconstructed before Limusaurus was known. Whichever way it cuts though, this is a great specimen in great condition and a lovely mount that shows off the material. You can also spot a really quite hefty theropod femur in the case behind it as well – this might be the only vaguely-complete theropod from Tendaguru, but it’s far from the only theropod known.


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