Clubbing

No, not what you think. I’m not going to talk about going out, drinking and dancing – while my blog sometimes strays pretty far from dinosaurs (for which I got scolded by a certain Peter F. from the UK), “clubbing” in that sense would be too far from the intended focus. Rather, today it’s time for a gem from the NHM in London.

Partial tail and tail club of Euoplocephalus tutus in the NHM’s Dinosaur Hall. The NHM has a very nice specimen that goes with it, an articulated individual of “Scolosaurus cutleri” (junior synonym of E. tutus), that is nearly complete – and nearly impossible to photograph nicely. Glass in the way, thanks to stupid visitors who couldn’t resist touching it.

Ankylosaurs are pretty crazy animals, and especially the nodosaurs have often been likened to tanks because of their proportions, likely speed of locomotion, and especially their massive dermal armour. However, a detailed study of said armour has found that in some groups the bones were rather fragile, and thus likely not armour against impacts at all (Hayashi et al. 2010).

But some taxa have quite massive tail clubs, as the one shown above shows. And that’s suggestive of, well, clubbing. Clubbing predators, clubbing each other, just bashing the hell out of things. And quite different from the stegosaurs, one of which, my guinea pig Kentrosaurus aethiopicus most likely used its tail tip spikes to give everyone stupid enough to get close its own version of hell. However, a long, slender spike is more useful as a penetrating or slashing weapon, and much less for a blunt impact – and creates very different kinds of trauma. For example, a massive armour shell is good for taking blunt impacts, but if it is to be mobile and thus must be formed by segments, the hinges between them are prone to allow a spike to slip in, with possibly fatal consequences. Think slipping a narrow blade between the plates of plate armour. For comparison, here is the tail tip of Kentrosaurus:

Figure 3 of Mallison (2011).

Before we delve deeper into the publications on ankylosaur tail clubs, let me just point out that the phylogeny of the group used to be a mess – lucky me I do not need to discuss it, though. Some people much more qualified than me just did, at length, in a paper just published in the Journal of Systematic Palaeontology. If you want an excellent walk-through of that paper, go to Dave Hone’s Archosaur Musings, where lead author Rick Thompson has a guest post up.

Estimating Impact Forces of Tail Club Strikes by Ankylosaurid Dinosaurs

Anyways, with this sorted out, and there have been a few studies looking at the business ends of ankylosaurs, too. The girl to talk to is Victoria Arbour from the Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada. Vic blogs here – go check out her stuff. She published a nice paper in PLOS ONE (back then still PLoS ONE – how I hate how they changed just because people were incapable of remembering “o, not O”), a paper titled Estimating Impact Forces of Tail Club Strikes by Ankylosaurid Dinosaurs. What Vic did was study the anatomy of the tails and clubs, including the internal structure (CT scans are so useful!), reconstruct the muscles, and estimate the forces the clubs could create via a formula previously used by Carpenter et al. (2005). Vic found that the tail consists of three section: one is mobile, one is stiff with highly aberrant vertebrae and lots of ossified tendons (which she calls the club handle), and one consists of a single transitional vertebra in between the two other sections.

As I have previously mentioned (Mallison 2011) I am not very happy with the Carpenter et al. 2005 method, not because it is not a good method, but because it was implemented with some flaws. Vic copied one of these, by using the half-width of the tail bones as the moment arm of the muscles – obviously, that’s not entirely correct because the area centroid of the muscles’ cross sections can’t be at their outer edge. But because the tails Carpenter et al and Vic reconstructed are likely much undermuscled – yes, even the “more muscular” version in Vic’s Figure 9 is probably not muscular enough – and thus the real centroid would have been further out than the one of the reconstructions is. Thus, part of the error regarding the moment arm is corrected by the error in the muscle reconstruction. Otherwise, if you really follow the method religiously and do not mix up Impulse and Force it is really good – in contrast to what Carpenter now says.

OK, that’s enough text to warrant another picture, so here is the above club as a digital 3D model. Photogrammetry again: 15 photos, Medium quality in agisoft’s Photoscan.

I was impressed by the program not being affected by the (slight) reflections on the glass cover and the stupid spotlights.

Obviously, the topic needs to addressed in more detail, which will have to wait for another post. Additionally, there are glyptodons, which apparently also lashed out with club-equipped tails. And there are even more animals with tail clubs, including some sauropods. Again, more later! And then there is the entire issue of clubless close relatives to cover…. oh my!

References

Hayashi, S., Carpenter, K., Scheyer, T.M., Watabe, M. and Suzuki. D. 2010. Function and evolution of ankylosaur dermal armor. Acta Palaeontologica Polonica, 55(2): 213-228.

Carpenter, K., Sanders, F., McWhinney, L.A., and Wood, L. 2005. Evidence for predator-prey relationships. Examples for Allosaurus and Stegosaurus, p. 325-350. In Carpenter, K. (ed.), The Carnivorous Dinosaurs. Indiana University Press, Bloomington.

Mallison, H. 2011. Defense capabilities of Kentrosaurus aethiopicus Hennig, 1915. Palaeontologia Electronica 14.2.10A.

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