Smithsonian.com

Part of a multi-step sequence by which Tyrannosaurus could have beheaded Triceratops, based on research by Fowler et al. Art by Nate Carroll.

For a dinosaur so terrifyingly powerful as Tyrannosaurus, there was no greater rival than Triceratops. Each was the acme of their respective lineage–one a hypercarnivorous bone-crusher, the other an immense three-horned herbivore. No wonder that artists, paleontologists, filmmakers and children on playgrounds have been pitting these dinosaurs against each other for over a century. Yet, despite how much we love to revel in the Cretaceous gore of such scenarios, we don’t really know whether Tyrannosaurus and Triceratops ever fought each other.

Earlier this week, Nature News reported on a delightfully gruesome Cretaceous vignette presented at the 72nd Society of Vertebrate Paleontology conference. After examining tooth marks on Triceratops frills, paleontologist Denver Fowler of the Museum of the Rockies in Bozeman, Montana, reconstructed how Tyrannosaurus could have torn the head off the great three-horned dinosaur to gain access to the herbivore’s succulent neck meat. There wouldn’t have been much flesh on the frill of Triceratops, Fowler pointed out, so it’s more likely that hungry tyrannosaurs used the bony collars for leverage to wrench the skull of the ceratopsid away from its body. Fowler also notes that he’s still studying these trace fossils and that a paper spilling the full details is in progress.

But the preliminary research only shows how Tyrannosaurus dined on Triceratops. Despite sensational ledes about the study that play up the “immortal battle” between the dinosaurs, the work doesn’t tell us anything about whether the enormous tyrant was capable of killing old three-horned face. Bitten bones and even fossil feces can help us fill out what was on the Maastrichtian menu for Tyrannosaurus, but they can’t tell us how our favorite Cretaceous carnivore acquired that meat.

Consider a damaged Triceratops pelvis described by Gregory Erickson and Kenneth Olson in 1996. The fossil was dotted with at least 58 punctures that were mostly likely created by an adult Tyrannosaurus. These were not injuries caused during predation, but they record the feeding behavior of a tyrannosaur as it ripped the hips off the Triceratops and  defleshed that mass of meat and bone as best it could. That’s as far as the evidence goes. Tracing those punctures back to the Cretaceous scene, the Tyrannosaurus is already standing over the felled Triceratops. What killed the Triceratops in the first place is a mystery.

So far, no one has found direct evidence of a Tyrannosaurus versus Triceratops battle. A healed bite wound on a Triceratops skeleton or an injured Tyrannosaurus bone corresponding to damage that could have only been made by a horn would provide paleontologists with a sign that these dinosaurs actually fought. After all, paleontologist Andrew Farke and colleagues recently found that tussling Triceratops  wounded each other, so there’s at least a possibility that Triceratops horns might have left tell-tale signs in the bones of an attacking Tyrannosaurus. For now, though, we are left with more indirect clues that will undoubtedly disappoint some dinosaur fans.

Tyrannosaurus was undoubtedly both a hunter and a scavenger. There is no longer any reasonable debate on that point. But, despite the dinosaur’s fearsome reputation, there’s no reason to think that Tyrannosaurus ate whatever it wanted. Tackling an adult Triceratops would have been a dangerous proposition, because of both the ceratopsid’s horns and bulk, so Tyrannosaurus might have avoided such risky encounters. Instead, as David Hone and Oliver Rauhut have pointed out, Tyrannosaurus and other large, carnivorous theropods may have preferentially hunted younger, less-imposing individuals, as well as the old and infirm. And there’s no reason to think that Tyrannosaurus would have passed up Triceratops carrion when the opportunity arose.

The ornaments of Triceratops don’t do much to help the predator-prey scenario, either. Although this dinosaur’s horns and frill have been characterized as weapons, the only direct evidence known of combat is for fights between adult Triceratops. Likewise, even though ceratopsids lived alongside tyrannosaurs for tens of millions of years, predator defense doesn’t seem to have anything to do with horn evolution. If horned dinosaurs developed horns to ward off attacks by big theropods, we would expect there to be an optimal form for defense, or at least severe constraints on the shapes of horns and frills so that they would still be effective. Instead, paleontologists have recorded a confounding array of different horn arrangements among ceratopsids, and the adornments appear to have more to do with communication within their species than defense against others. This is just as true for Triceratops as other horned dinosaurs. While some horns are better than none when confronted by a tyrannosaur, there’s no indication that the ornaments evolved as a predator defense strategy.

We need to reimagine what a confrontation between Tyrannosaurus and Triceratops would have looked like. Instead of two equally matched dinosaurs squaring off against each other, adult Tyrannosaurus probably ambushed young, unwary Triceratops or picked off sick individuals too weak to put up much of a fight. Tyrannosaurus had no sense of honor to uphold–the tyrant was an apex predator that had to maximize its chances of acquiring flesh, and the only safe adult Triceratops was a dead one. Perhaps, someday, a lucky researcher will stumble across evidence of our favorite Hell Creek scene at a field site or in a museum drawer. For now, though, we need to consider the magnificent Tyrannosaurus and Triceratops as real animals and not slavering monsters made to gore each other for our delight.

References:

Erickson, G., Olson, K. 1996. Bite marks attributable to Tyrannosaurus rex: Preliminary description and implications, Journal of Vertebrate Paleontology, 16:1, 175-178 DOI: 10.1080/02724634.1996.10011297

Farke, A., Wolff, E., Tanke, D. 2009. Evidence of Combat in Triceratops. PLOS ONE 4(1): e4252. doi:10.1371/journal.pone.0004252

Fowler, D., Scannella, J., Goodwin, M., Horner, J. 2012. How to eat a Triceratops: Large sample of toothmarks provides new insight into the feeding behavior of Tyrannosaurus. Society of Vertebrate Paleontology 72 poster.

Holtz, T. 2008. A Critical Reappraisal of the Obligate Scavenging Hypothesis for Tyrannosaurus rex and Other Tyrant Dinosaurs, pp. 370-396 in Larson, P. and Carpenter, K. (eds) Tyrannosaurus rex: The Tyrant King. Bloomington: Indiana University Press.