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.

Elaphrosaurus

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.

My very own Zhuchengtyrannus

As I have noted on here before, the Japanese really do love their toy dinosaurs and produce really high quality models on a regular basis and of all kinds of obscure and wonderful critters. So when a couple of weeks back I got a cryptic e-mail from Matt Lammana of the Carnegie about having a gift for me from China connected with one of ‘my’ dinosaurs, I did have to wonder if, just possibly, there might be a Zhuchengtyrannus out there. Last night I found out that indeed there was. It had arrived through the post while I was away at SVPCA (more to come there) and well, how can I not be more chuffed. There’s a real toy Zhuchengtyrannus!!

It’s tiny (just 10 cm or so) but obviously well modeled and the paint job ain’t too bad either. Rather obviously taking the lead from Yutyrannus, it’s on the fuzzy side of feathering too. Now obviously the holotype is incomplete to say the least, and so we’re left with a rather typical tyrannosaurine for a model really. Still, I *know* it’s a Zhuchengtyrannus as, if you look closely, you can see it’s written on the base.

My thanks of course to Matt for this wonderful little present, made my day to say the least. On a not entirely unrelated note, there’s a palaeoart event going on at the NHM next week in conjunction with the Dino Art book launch. See here for more details. I hope to be in attendance but Luis Rey, Bob Nicholls, John Sibbick and others will be there.

Deinonychus at the AMNH

Since the theropods are doing well this week, it’s time to wheel out another image kindly sent in by Steve Cohen. I suspect there’s a nice mount of Deinonychus in a great many museums in North America, but for all my traveling, I’ve only ever seen two of them (part shown here) and didn’t have time to study either in any detail. Here though is an excellent and indeed famous mount in the AMNH of this dinosaur and it would probably be even more impressive if Steve hadn’t sent this to Heinrich Mallison as well and he’d not put it up a couple of weeks back….

Suchomimus

Yesterday I spotted a nice picture of a mount of Suchomimus on Twitter posted up by artist Brett Booth. On asking he was kind enough to provide me with the full set of things he’d taken and gave me permission to post them up. Years ago I got a chance to see a cast of the manus of this animal, but at the time I didn’t know much about dinosaurs and ironically the one other theropod I’d seen much of was Baryonyx, so the interesting robustness of these things rather passed me by.

Spinosaurs are popular and have done well in the last couple of years. In addition to Oxalaia last year we also have recent had Icthyovenator and Ostafrikasaurus and that’s before we mention the most important spinosaurid find of recent years (according to me) – half a tooth. However, while the ranks of the spinosaurs has been growing, Suchomimus remains the the most complete spinosaur known to date with most of the skeleton having been recovered compared to the masses of vertebrae, snouts and teeth that characterise rather too many of them. Only Baryonyx really comes close in terms of completeness, that that does at least have the advantage of having a good full description of the material.

Still, Brett’s photos help there as there are some nice ones. This looks to me like a good cast of the holotype material and there’s a bonus at the end of what looks like an original arm next to a human and T. rex for comparison. I actually forgot to ask Brett if he knew what the status of the mount was, or for that matter where this is being exhibited, but I’m delighted to be able to put it up here.

Late edit: Brett tried to add a comment but if having troubles. He sent me this in an e-mail that answers a few of my comments and queries:

This was at Lynx Exhibits in El Paso Texas, part of that traveling Supercroc exhibit. I believe it leaves after this weekend. It was on some sort of rig that would move if you pulled a few levers. Totally worth the trip!

The arm is original except for the metacarpals and first claw (the parts in blue.)

What didn’t come out was all the pitting and lines on the spine, very much like a stegosaurus plate. And there was some damage or warping to the pubis.

I have to say this was a HUGE animal. I was far more impressed with the size of this than I was when I saw Sue. I hit the knee and I’m 6’3″. Really impressive.

Guest Post: Yurgovuchia doellingi

Those keeping up with the scientific literature will know that a new dromaeosaur was described just the other day. One of the authors, Jim Kirkland, has been kind enough to pen a few lines about the discovery and has included some nice photos of the excavation too. Enjoy:

Extra final bonus Gorgosaurus preparation post

Well, it has been a while since the last post where we finally rounded up and summarised Darren’s massive series of posts on preparing a Gorgosaurus specimen. Here Darren summarises the prep work done since and provides new photos of the skull now seen from the others side.

After a long hiatus, I update the Gorgosaurus preparation series, with this, the final installment. Since the last posting, the entire specimen, and select parts thereof were moulded in a high-quality silicone rubber compound so detailed casts of the specimen can be made in the future. After the moulds were removed, the entire specimen was covered in a separating layer of wet tissue paper, and then plastered over and flipped over.

The side now facing up is that which faced up in the field. As this is the upward-facing side, and there was only low rock overburden in the field, this side of the skeleton was more exposed to the effects of rain, frost, rock fracturing and rock expansion/contraction from summer heat (up to +40C) and cold winter temperatures (down to – 40C). Because of this, this side of the specimen is less well preserved, in fact I’d say in many places it is poorly preserved- in some areas the bone is like the consistency compressed hot chocolate powder. Bones are also badly crushed in many places. If I can remove the equivalent of a sugar-cube sized piece of rock per day, that is pretty good going as I super detail the many bones preserved. The skull, being better ossified, was in better shape, but the bone quite splintery in places. This means the work has proceeded very, very slowly. The tools and techniques were much the same as in earlier postings, though much of the work is being done with a head-mounted magnifying lens and later, probably microscope work. Also the work has to go much slowly. It can be seen that the posterior right side of the face is missing. This is because as the carcass rotted, the side of the head, exposed to water currents, was disarticulated and piece by piece the bones were washed away. We have a couple of them, but are missing 6-7 to make a full skull. However, we get a beautiful side view of the braincase which is important for researchers. We had the whole skull CT scanned recently and really nice images resulted for study by one of the Royal Tyrrell Museum scientists.

Preparation work on this side has also revealed some anatomical details that are important to future scientific study and eventual publication(s) that cannot be shared here or at this time and therefore, this series must end with this posting. I have been happy to share the preparation of this gorgeous little specimen with you all and hope you learned something about the intricacies of fossil preparation.

Best, Darren Tanke, Senior Technician II, Royal Tyrrell Museum, Drumheller, Alberta, Canada.

As usual all images are copyright to Darren / the Tyrrell Museum.

More on dromaeosaurs vs azhdarchids

Yesterday I covered the basic introduction to my new paper about a Velociraptor specimen with an azhdarchid element preserved in it’s gut. Today I want to move on from the basics (what is there) to what this potentially means and how this is inferred. Most of my recent research is based around theropod ecology and behaviour (like this, this and this for example) and specimens like this one can provide new information and evidence for how these animals were acting. The obvious question here is why is this inferred as scavenging and not predation? As usual with such questions going so far back in time, it’s hard to be definitive, but this is the better supported inference.

First off there is the relative sizes of the animals. While it’s not unknown for predators to tackle other predatory animals, or relatively big prey it’s certainly not normal. Lions don’t routinely hunt leopards or bears go after wolves. This is relevant here since azhdarchids were most likely active predators themselves and so a potentially dangerous animal to attempt to kill. Moreover, the azhdarchid in question was most likely 9 kg in weight with a 3 m wingspan (and could have been considerably larger), while the Velociraptor was a sub-adult of around 13 kg. In short if this was a predation it was no mean feat – perhaps the equivalent of a small coyote bringing down a big eagle. Sure it’s possible, but it’s not unreasonable to think this was really very unlikely. It’s more likely this was a young carnivore scavenging on the carcass of a dead pterosaur, as indeed was inferred for a similar previous specimen from Canada.

Even if we assume that it was a kill, other things don’t add up well to support this. Theropods don’t tend to consume large amounts of bone like this. They might consume relatively large items (like a whole small prey item) but not large chunks of bone like this. And it is a pretty big chunk of bone, probably the same length as the skull of the dromaeosaur. Moreover, we also know that theropods can be really quite delicate feeders, including other velociraptorines. The tendency seems to be to scrape meat free of the bones, now chew up and swallow whole ones (like modern birds of prey, they’ll swallow a mouse, but will pull chunks off of rabbit or sheep). Carcass consumption patterns by modern vertebrates also show that whole big bones like that don’t tend to be swallowed. Finally, the pterosaur weighted at least half and potentially more than the dromaeosaur. Given their apparent skill at stripping a carcass of meat I don’t think I dromaeosaur would be swallowing whole bones (and ones that would be pneumatic, not filled with marrow) when much of it’s own weight was sitting there in muscle and viscera.

In short, predators don’t normally predate other predators. Predators (including theropods) don’t usually seek out large prey. Predators (including theropods) don’t usually consume large bones of large prey unless they are a bone specialist or there’s nothing left. Even when there’s not much meat left, theropods tend to scape this free to eat rather than swallow bones. Sure all of these could hit the ‘least likely’ option and it’s a who-knows-what to 1 chance that a small dromaeosaur took on a big azhdarchoid, killed it and started swallowing big bones. But it’s far more reasonable to infer that it scavenged the last bit of a carcass it chanced across.

We are then left with scavenging as the most likely explanation as to why this animal was swallowing whole bones. Interestingly, we do also see shed teeth being a common feature of dromaeosaur (and indeed theropod in general) feeding yet here every tooth in the skull is intact. That is admittedly merely a soupscon of evidence for scavenging, but one might well expect a tooth or two to be lost during a fight with such a big adversary. or even biting through bones to swallow them again suggesting it just picked up and swallowed what it could find without much or any oral processing.

Uncoloured version of Velociraptor feeding. Courtesy of, and copyright to Brett Booth.

Moving on from this issue then, what does this tell us about the ecology of dromaeosaurs? Well to  degree, not much we didn’t know already. There’s already evidence for both predation and scavenging in the dromaeosaurs, and indeed already evidence they were eating pterosaurs. Even so, more evidence is always good, and it does at least reinforce the existing evidence we have. It also therefore takes us a little further away (sadly) from the idea that dromaeosaurs were some kind of hyper-carnivorous super-predator that spent their time knocking down huge prey items with all their claws and teeth. I say sadly, because it’s a great idea and a wonderfully romantic notion, but sadly these animals were every bit as opportunistic as other carnivores and clearly were not beyond taking the odd, or indeed regular, free meal through scavenging. Indeed given the number of specimens we now have supporting a scavenging interpretation, this does seem to have been a pretty common part of their behavioural repertoire as carnivores.

Arctometatarsal origins

A comment on my recent post about alvarezsaur arctometatarsals made me realise there was a bit more scope for talking about this issue of the origins of this structure. Arctometatarsalian pedes are known in tyrannosaurs, troodontids, alvarezsaurs, ornithomimids and oviraptorosaurs. In other words a pretty big selection of derived theropods have at least some taxa with this condition.

This begs the obvious question of whether or not this is homologous? After all, this could easily plot on a cladogram as originating before the tyrannosaurs and being maintained throughout the derived theropods only to be lost in therizinosaurs and droimaeosaurs + birds. However, there are two good reasons to think that this convergence and not homology with the characteristic being acquired multiple times.

First off are the details of the actual pes. Although obviously we would expect different lineages to adapt and modify such a structure independently, there are some very clear differences between quite how the middle metarsal is pinched and in which way by which of the surrounding elements. It’s subjective of course but they do look quite different in form.

Secondly and more importantly, the character is not shared by all of the taxa in those various groups and especially not basal forms. Early tyrannosauroids like Dilong and Guanlong don’t have it, nor does the basal alvarezsauroid Haplocheirus, and it’s not present in at least some early troodontids, ornithomimids or oviraptorosaurs. So it is not a simple plot of acquisition before tyrannosaurs and occasional lost, but instead more parsimonious to infer that it has been gained independently multiple times (each with a slightly different form) than been lost multiple times in all those basal forms (i.e. lost in each of Guanlong and Dilong and any other tyrannosaurs or even lost at the base and then acquired again) and been modified repeatedly along each lineage.

What has drive this convergence is likely the benefits of such a structure. Work on the functional morphology of such a foot suggests that it increases running efficiency and may also provide increased turning ability. In short, this is a feature of active runners, something that certainly matches at least some other anatomical specialisations seen a number of these groups.

A different oviraptorosaur

A rather different oviraptorosaur to the last one, though I’m not sure what this is either. It was (I think, I saw this two years ago) labelled as Oviraptor, though the oft confusion in terms of separating the very similar Oviraptor from Citipati and the general low quality of the mount makes me suspicious that this isn’t what it says it is and my lack of knowledge over the distinctions between the two means I might not know. Anyway, as usual lacking any evidence to the contrary, I’ll go with Oviraptor.

Incidentally, the mount is in one of the endless small museums down in Liaoning. There are so many in fact, I can’t remember exactly which one this is, though I think it’s the main one in Jinzhou.

Guanlong

This is the skull of the Middle Jurassic tyrannosauroid Guanlong, the crested dragon. Or more specifically it’s the skull of the referred specimen, a near complete juvenile animal that’s in nearly as good condition as the adult. One thing it lacks though is the famous crest of the genus. While this could be put down to ontogeny, a look at the skull in dorsal view shows obvious signs of damage and there was most likely some form of crest here originally, though probably rather less well developed than the adult.

An oviraptorosaur

This is a mount that stands on display in the Carnegie and has no name attached to it. The reason is quite simple – the specimen has yet to be formally described. The consensus is that is a new taxon and will be getting a name in due course. However, having not actually seen the original material (well, beyond a few bits) I don’t know how complete this is or which bits of the mount are reconstructed (though I’d guess the skull is all sculpted).

Oddly enough, I saw this (or perhaps a duplicate) in Japan a few years ago as part of a touring exhibit. I’d wondered what it was then as I didn’t know which taxon it belonged to, only of course to later discover it hadn’t been named. It does hinder your ability to diagnose something when it’s not actually in the literature.