It’s a New Paper Day today! Go check it out at the new open access journal FACETS!
An alternate title I kicked around for this paper was “Victoria thinks about Ankylosaurus for a while: What does she know? Does she know things?? Let’s find out!”, because in the end this represents lots of little odds and ends about the most famous of ankylosaurs accumulated since about 2008 until they felt like they gelled enough to make a proper paper out of. In this paper, Jordan Mallon and I tackle some of the more frustrating aspects of Ankylosaurus: what does this animal really look like, what’s up with its weird giant skull, and how did it live?
Here’s a copy of the World’s Fair Ankylosaurus at the Royal Alberta Museum before the museum’s move to the new building – I know it’s partner the Corythosaurus has moved to Jurassic Forest, but I’m not sure where this guy is winding up! Maybe he’ll be at the new RAM?
Despite Ankylosaurus being one of the most famous dinosaurs (it was one of the Sinclair World’s Fair dinosaurs, after all!), it’s really not known from very many specimens. While its slightly earlier relatives Euoplocephalus and Anodontosaurus are known from multiple skulls and skeletons, only three good specimens are known for Ankylosaurus (unless someone out there has a secret one in their collection that I don’t know about!). AMNH 5895 is the holotype, and has the most complete postcrania, no tail club, and the worst skull. AMNH 5214 is the best skull, the only known tail club, and is also the smallest specimen. And CMN 8880 is represented only by cranial material, but is absolutely colossal.
Ankylosaurus is the ankylosaur I am most often requested to consult on for various media projects (weirdly, the runner-up is Edmontonia, despite it being a lesser nodosaur), and it’s a dinosaur that shows up in lots of art and documentaries. Back in 2008 I helped out with the Ankylosaurus for Clash of the Dinosaurs, and I’m pretty sure that model was subsequently re-used for Last Day of the Dinosaurs (which features a hysterically outrageous ultimate showdown between Ankylosaurus, Triceratops, and Tyrannosaurus that’s a must-see, but warning, it’s gross).
And most recently, the good folks at Saurian asked for my input on their Ankylosaurus. Despite the popularity of this species, it’s really hard to get a good handle on Ankylosaurus – there are no specimens with the osteoderms in situ, it’s got some weird proportions, and all of the specimens are very fragmentary. Several authors have explored the anatomy of Ankylosaurus, and in particular Ken Carpenter provided a great overview of the known skeletal material in a 2004 Canadian Journal of Earth Sciences paper. Nevertheless, this was a good opportunity for me to revisit what I’d observed over the years and try to come up with a really good reconstruction of this dinosaur, so I dug out all of the photos and papers I’ve accumulated over the last decade and took a stab at refining Saurian’s initial model. You can read a bit about the process in this blog post from last summer! The result is, in my opinion, the most convincing reconstruction of Ankylosaurus out there right now, complete with a best-guess armour arrangement based on more complete specimens like Saichania, Pinacosaurus, and Zuul, scales based on skin impressions from Albertan specimens, and new interpretations of things like the cervical half rings in the original Ankylosaurus specimens themselves. The final full-colour render has a lot of personality and I’m looking forward to playing the game as this species in the future!
Assisting with this digital model made me realize that it was probably time to publish an updated hypothesis of Ankylosaurus armour, and so here we are! I’m sure this won’t be our final view of Ankylosaurus, and hopefully as we get more specimens future palaeontologists will be able to build on this work as we’ve done here. I’m really happy with this art-technology-science collaboration, which was both a fun project and also scientifically illuminating. You can follow Saurian’s updates on their Ankylosaurus model, which will be a playable character a bit further down the line, as well as more information about their interactive Hell Creek ecosystem, here.
Elsewhere in Ankylosaurus, how about that weird giant skull? Ankylosaurus shares a lot in common with Laramidian ankylosaurins like Euoplocephalus, Anodontosaurus, and Zuul, but when it comes to the nose Ankylosaurus is doing something very different and weird. Instead of having forward-facing nostrils, the nostrils are pulled backwards and roofed over by cranial ornamentation so that you can’t even see them when you look at the skull face-on. Why has Ankylosaurus done such a weird thing to its face? We can’t say for sure, but when we look at other animals with somewhat similar faces, the closest comparison we could come up with were the unusual subterranean amphisbaenians and scolecophidians. Some of these lizards have narial openings that look a lot like those of Ankylosaurus, broadly speaking. Ankylosaurus wasn’t a fossorial, burrowing dinosaur – but maybe it was foraging around in the earth, eating tubers, roots, and insects, instead of relying more on ferns and leaves for its diet. It’s speculative for now, but I think there’s still a lot to investigate around ankylosaur diets!
Why the weird face, Ankylosaurus? See how the nostril is located pretty far back on the side of the skull? The turquoise ‘mustache’ represents the ornamentation that usually forms an arch above the nostrils at the front of the snout.
Finally, let’s talk about the giant size of Ankylosaurus. The smallest skull of Ankylosaurus, AMNH 5214, is already a pretty big guy – much larger than any other ankylosaur skulls, even relative big ones like Zuul’s. But the largest skull, CMN 8880, is gigantic. It takes up an entire wood pallet in the CMN collections, and is about twice as big as most other Laramidian ankylosaurins. So just how big was Ankylosaurus? Previous estimates have put it in the range of 6.5 – 7.5 m long. Scaling the known skeletons of Ankylosaurus to more complete ankylosaur skeletons gives us maximum lengths up to an incredible 10 m! Only more complete skeletons can help us fully resolve this question, but given that Zuul’s skeleton is about 6 m long at minimum while the skull is substantially smaller than those of Ankylosaurus, I think a large Ankylosaurus in the range of 8-9 m isn’t an overestimate. Truly, the Hell Creek was a time of dinosaur behemoths.
Ankylosaurus skulls: pretty big!
A tail club is only known for the smallest Ankylosaurus, which led me to wonder just how large the tail club knob could get in this species. Anodontosaurus has one of the largest known tail club knobs for any ankylosaur, at 60 cm in width, yet the largest skulls are only half the width of CMN 8880 – thus, scaling the knob based on skull proportions between these two species would yield an Ankylosaurus maximum knob width of 120 cm, which must surely exceed some threshold for mass you can support at the end of a long tail. On the other hand, scaling between Ankylosaurus specimens yields a knob width for CMN 8880 of about 57 cm, which is similar to the largest known tail club knobs from Alberta and Mongolia. So, despite the large difference in skull size for Ankylosaurus, it seems like tail club knobs may have topped out around 60 cm in width, which is pretty interesting.
Ankylosaurus tail clubs: surprisingly not that big! On the left is the biggest Anodontosaurus tail club AMNH 5245, and on the right, the only known Ankylosaurus tail club, from AMNH 5214.
There’s lots more to dig through in this paper, so I hope you’ll go take a look for yourselves! And Jordan was even able to swing getting some fancy 3D scans of the giant CMN 8880 skull that you can download for yourself at MorphoSource – enjoy!