I can’t let this story go without commenting on it. Following the Society of Vertebrate Palaeontology’s most recent conference, news wires across the Internet have been running a story most-often called “How to Eat a Triceratops”. The story is based on work in progress by Fowler et al on the discovery of a number of postmortem scratch marks on the face, skull, and crests of the Triceratops specimens they were finding. The marks show that Tyrannosaurus was tearing the heads off Triceratops and eating the tasty flesh off the back of the skull where the nervous system passes through to the brain case.
Let’s pause for a moment and think about that: whether the Tyrannosaurus killed that Triceratops or found it, that’s a really impressive – not to mention terrifying – image.
I absolutely cannot wait for this paper. I’m hoping it will go into details such as whether the bite marks indicate a smooth, directed grip & pull or whether Tyrannosaurus employed the grab & shake free method – as demonstrated by this feisty, little, blind Jack Russell. Picture that: a Tyrannosaur worrying a carcass, upper body threshing side to side with the momentum created by the force of her neck movements.
What the paper probably won’t mention is whether extra steps are needed before decapitating a Triceratops: Ripping an animal’s head off is difficult at the best of times. Harder still when it has a neck as thick as a Triceratops (estimated 4/5ths the width of the back of his crest1). Tyrannosaurs are strong but are they so strong they can pull apart healthy, intact flesh? Tests could be done to see what force is required to accomplish this, using butcher-shop cadavers and scaling up the forces required according to the neck diameters. There aren’t many contemporary animals with a handy grab handle, like the Triceratops crest, to reproduce the twisting direction of the force unfortunately but I’m sure something could be rigged up.
Whether Tyrannosaurus could theoretically do this, from a biomechanical perspective, is one thing; whether it needed to is quite another. The act of decapitation will ruin the neck anyway, so there is nothing to suggest that Tyrannosaurus was particularly fussed about keeping it intact. If you compromise the structural integrity of the neck, you make it a lot easier to rip the head off. To demonstrate this: try tearing a tea-towel with your bare hands; now cut a small nick in it and try tearing it again.
The next question: what part of the neck do you have to sever before the head will come off? A Triceratops lying prone on its side has a beautifully exposed throat. The simplest way to compromise neck structure would be to take a mouthful of windpipe and crunch down hard. There’s a problem though: the ridiculously tough parts of any neck are not in the throat, they’re on the other side. Animals that need to hold their heads up for extended periods of time need a way of doing so that expends minimal energy. Giraffes and horses have a spongy muscle connecting the skull and the back. I mention this muscle in my Pony Dissection post but, in a nutshell, the M. Spinalis Capitis acts as a suspension bridge supporting the head’s weight. Ceratopsians hold the record for heaviest terrestrial skulls of all time, they’re going to need a lot of spongy muscular support. When you pull on the head of a dead pony, with its neck muscles intact, you end up dragging the entire body before you can get its neck to bend. If we are to assume that Tyrannosaurus did not cut through this muscle during feeds, we have to first demonstrate how a carnivorous biped can pin down a large carcass with its own body weight – while simultaneously tearing at one end. One for the biomechanics to answer but my hunch says it would mitigate its pulling efforts to compensate, so-as to avoid pulling itself off balance. So we can deduce that there is a cost attached to not severing this muscle and no benefit to keeping it intact. Can we say that Tyrannosaurus had the means to sever it? We know it had the bite strength2. It remains to be seen whether the cervical vertebrae of these specimens demonstrate applied use of that bite force, or whether Tyrannosaurus nibbled away delicately – as seen elsewhere with its Asian cousin Tarbosaurus bataar3. A glance at the proportions says Tyrannosaurus’ snout could wriggle between the crest and back – especially with the cleft being not all that deep – but I’d really like to take some proper measurements before I say for sure. We also have the possibility of Tyrannosaurus jabbing at the area with its toe like a cassowary or secretary bird (possibly while holding the crest steady with its teeth?). Lots to test before we call that a likely scenario.
I haven’t really talked about cooperative behaviour in tyrannosaurs because it’s mostly superfluous to the discussion but if, like me, you were thinking that some tyrannosaurs could pin the carcass down while another pulls its head off – there’s another group feeding scenario to consider: one tyrannosaur holding the Triceratops crest away from the body while the other bites/kicks through the back of its neck.
1. Tsuihiji, T. (2010). “Reconstructions of the axial muscle insertions in the occipital region of dinosaurs: evaluations of past hypotheses on marginocephalia and tyrannosauridae using the extant phylogenetic bracket approach.” (PDF). The Anatomical Record 293:1360-1386 (2010)
2. Erickson, G.M.; Van Kirk, S.D.; Su, J.; Levenston, M.E.; Caler, W.E.; and Carter, D.R. (1996). “Bite-force estimation for Tyrannosaurus rex from tooth-marked bones”. Nature 382 (6593): 706–708.
3. H.; Watabe, M. (2010). “New information on scavenging and selective feeding behaviour of tyrannosaurs”. Acta Palaeontologica Polonica 55 (4), 2010: 627-634 doi: http://dx.doi.org/10.4202/app.2009.0133