Tyrannosaurus and its relatives enjoy a reputation as bloodthirsty killers, always on the rampage and butchering the nearest, and generally largest, herbivores in the area. This impression is not without a fair bit of exaggeration and the endless depictions in documentaries looking for spectacle more than accuracy. However, the larger species were certainly capable of delivering very powerful bites that could puncture into bones and these form an excellent record of what was bitten and how. Unsurprisingly these mostly show damage to animals that would have been common items on the tyrannosaur menu, but actually there are a number of bite marks on other tyrannosaurs – both living and dead.

In a new paper I have published today with my co-author Darren Tanke, we describe a specimen of the tyrannosaur Daspletosaurus from Alberta, Canada that uniquely shows bites marks inflicted by other tyrannosaurs both during its life and after it had died. Daspletosaurus was nearly as large as its more famous cousin, though this animal was not fully grown and would have been around 6 m long and half a ton when it died. As with a number of other tyrannosaurs, there are numerous injuries to the skull that show signs of healing – so must have taken place while the animal was alive. These include punctures and breaks on the bones and one part at the back of the skull has actually been snapped away and the remaining piece has healed up.

The injuries are quite extensive and while perhaps not all were the result of scraps with other tyrannosaurs, clearly a number were and they were quite serious. The larger tyrannosaurs are great for this kind of study as generally the only other large carnivores in their environments were other tyrannosaurs, so it is easy to rule out other candidates as having been biting on them. In the case of Daspletosaurus, there was another tyrannosaur – Gorgosaurus, that lived alongside it and could have been responsible, but it seems more likely such a face-to-face encounter happened between two members of the same genus. Notably there are no marks on the rest of the skeleton, everything is on the head, so this does imply some kind of real fight was going on here with animals facing off or perhaps standing side by side – bite marks are typically not found on the heads of herbivores.

A post mortem bite to the right lower jaw. The black arrows point to scrapes by teeth along the inside of the bone and the white arrow shows where the upper edge of the jaw has been broken and fragments of this have been forced down and wedged into the tooth sockets. Photograph: Darren Tanke/Hone & Tanke 2015

One bite is also present on the right side of the jaw with several scrapes across the bone from the teeth of a large tyrannosaur and several associated broken pieces showing a serious impact occurred. These injuries don’t show any signs of healing, and thus occurred after death. The arrangement of the skeleton in the quarry and the fact that teeth from the missing right jaw are still present show that at some point the other side was removed, even though there’s no good evidence for strong currents where the fossil was buried. In short, one jaw was bitten and the other apparently removed, and this must have been quite some time after death for the ligaments holding the teeth in the jaws to have rotted and allowed the teeth to spill out. This suggests scavenging of the carcass - it can hardly have been fresh at this point and nor would the jaws normally attract much interest, there would be much meatier areas on a recent corpse.

Reconstruction of combat between two Daspletosaurus Photograph: Luis Rey

Tyrannosaurs clearly had something of a rough life – an increasing number are being found showing facial injuries apparently received in combat from other tyrannosaurs, and this includes relatively young animals like this Daspletosaurus. In the case of this individual, in addition to having taken something of a battering in life, it was also then at least partially eaten by another tyrannosaur (which may or may not have been another Daspletosaurus). That’s certainly a rarity in the fossil record and this kind of information is really useful to build up a picture of how these extinct animals lived, and died, and their interactions with one another. It can be a difficult process, but we are generating an ever clearer picture of ancient ecosystems and the behaviours of the dinosaurs that lived in them.

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. Peer, 3, e885.