- Poster presentation at Society of Vertebrate Paleontology (SVP) 2012 annual meeting (17th-20th October; Raleigh, North Carolina) -

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ABSTRACT

Toothmarked bone, created by the feeding behavior of carnivorous dinosaurs, provides direct evidence of ecological interaction between predator and prey. However, examples are typically limited to small sample sizes, restricting behavioral inferences for specific taxa. In this study, we present one of the largest samples (n=18) linking a single carnivore, Tyrannosaurus (Tyrannosauridae), with the prey taxon, Triceratops (Ceratopsidae), revealing consistent patterns of carcass processing. Approximately 100 Triceratops specimens have been collected from the Late Maastrichtian of Montana as part of the multi-institutional Hell Creek Formation Project (1999-2011). From this, toothmarks were identified on eleven individuals of Triceratops, with possible toothmarks on an additional seven individuals. With the exception of two ilia, all toothmarked elements are from partially to fully disarticulated complete or partial skulls. Although the total sample includes many Triceratops collected from sandstones, all toothmarked elements are derived from mudstones. In the absence of any signs of healing, all toothmarks presumably formed during postmortem carcass processing.

Specimens exhibit a suite of puncture, score, gouge, and puncture-pull marks, which in combination with tooth-spacing patterns are similar to traces previously attributed to tyrannosaurid theropods. This supports our assignment of these scars to Tyrannosaurus, the only accepted tyrannosaurid from the Hell Creek Formation. Two unassociated juvenile squamosals exhibit extensive punctures up to 2cm wide, and puncture-pull marks up to 10 cm long. An associated young subadult juvenile squamosal and parietal show multiple parallel score marks. These might be unexpected as the parietosquamosal frill would have been mostly bone and keratin, yielding little edible flesh. However, the marks may have been formed as the Tyrannosaurus attempted to move the frill to access the generous neck muscles connected to the skull. This would be consistent with deep parallel gouge marks observed on 4-6 occipital condyles, one associated with a punctured braincase. By contrast, three to four short, parallel score marks on an unassociated nasal and 2 premaxillae are more consistent with delicate and precise bites from the incisiform premaxillary arcade.

The laterally thickened teeth of adult tyrannosaurids appear well-suited for resisting lateral stresses, which may have enhanced their ability to dismember carcasses. Relatively older Tyrannosaurus individuals may have employed different feeding strategies than younger individuals as their tooth morphology thickened with a concurrent reduction in total tooth count in the dentary.

(Purple text is altered from the published abstract; we have discovered additional toothmarked specimens in the time between the abstract submission (April 2012) and poster presentation (Oct 2012); also the terminology used to describe the marks has been revised to be more precise).
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AUTHOR NOTES ON PRESS COVERAGE :

Nature News: "How to eat a Triceratops: Tyrannosaurus tore the head off armoured prey to reach the tender neck meat."; October 24th 2012; Matt Kaplan.

New Scientist: "Tuck into a Triceratops"; October 27th 2012 (issue 2888; page 9); Jeff Hecht (online version requires registration / behind paywall).

The real meat of this study will be presented upon publication in a peer-reviewed journal
There has been a small amount of press interest in the poster that we presented at SVP 2012. Obviously the subject matter (Tyrannosaurus eating Triceratops) has potential for public interest, and the consequent press coverage is very welcome (thanks!). However, I want to emphasize the difference between promotion of a meeting abstract with that of final published work.

We used the SVP poster session to get some feedback from other researchers; all feedback was very much appreciated, and the final MS will be much better for it. Specifically, I was hoping to get some information as to how to nail down the mark maker more confidently, and hear any alternative hypotheses that we may not have considered. The poster featured photos of the 10 new specimens that exhibited the best preserved toothmarks (from a total of 18 toothmarked specimens). For many marks, Identity of the mark maker is consistent with Tyrannosaurus and inconsistent with large crocodiles; for other marks it may not be possible to differentiate between a large crocodile and Tyrannosaurus. However, large crocodile remains are relatively rare in the Hell Creek Formation where this material was collected, and many of the marks are unlike what is expected for crocodiles. No visitors to the poster disputed that the majority of marks were most likely made by Tyrannosaurus, but for some marks, this is down to a probability, rather than a definite yes or no. The accuracy of our identifications will be assessed when the final manucript is subjected to formal peer-review.

Any inference of behaviours in extinct organisms is often passed off as arm-waving, or as something we cannot know based on evidence. We feel that our dataset is robust enough to make some inferences about behaviour. The specimens represent data: ie. they are direct evidence of something an animal actually DID, rather than the results of computer modelling that shows what an animal MIGHT DO. If a computer model is correct, then it would hopefully make accurate predictions about what we should see in fossils; our findings seem to be consistent with explicit predictions made by the biomechanical models of Snively and Russell (2007abc). Also, if you only have an isolated specimen with bitemarks, you can make a suggestion of what the carnivore was doing in that specific case, but you can't tell if the bitemarks represent typical or atypical behaviour for the carnivore's species. Our study observed the same kinds of marks made on the same skull elements across multiple specimens; hence the same behaviours are being observed repeatedly. This suggests consistent patterns of behaviour for carcass processing that may characterize Tyrannosaurus feeding strategy. The final MS will describe these behaviours in greater detail, which can only be properly asserted after having been subjected to formal peer-review.

So in summary: It's really nice to get press interest (I appreciate it a lot); it's great for the public to get a sneak preview of upcoming research and insight into the process of science, but our poster presentation doesn't count as research until it has passed peer-review and been published in a reputable journal.

In the meantime, if you enjoyed reading about Tyrannosaurus feeding behaviour, you might like to read about our recent published paper (Fowler et al., 2011b; CLICK HERE) on the feeding behaviour of another theropod Deinonychus (related to Velociraptor):
This research contains more graphic artwork by Nate Carroll depicting predatory behaviour of theropod dinosaurs.

Also, check out the Horner Lab Facebook page: every week or so we post photos of new dinosaur specimens, fieldwork and prep lab, plus details of new research.