October 26, 2012
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.
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.
Hone, D., Rauhut, O. 2009. Feeding behaviour and bone utilization by theropod dinosaurs. Lethaia 43.2 (2009): 232-244.
August 31, 2012
Earlier this week, I got into a snit over the blinkered assertion that feathery dinosaurs are lame. I argued the opposite point–as I wrote at the time “Feathered dinosaurs are awesome. Deal with it.” How fortunate that a new paper this week offers proof of fuzzy dinosaur superiority. The evidence comes in the form of gut contents found within predatory dinosaurs that stalked Cretaceous China around 125 million years ago.
The carnivores in question are a pair of Sinocalliopteryx. These dinosaurs were close cousins of the much earlier Compsognathus, albeit quite a bit larger. While Compsognathus was turkey-size, about three feet long, Sinocalliopteryx grew to be about eight feet long. And this big predator was fluffy. The original description of the dinosaur mentioned the vestiges of simplified dinofuzz around the body of Sinocalliopteryx, and this makes sense given the dinosaur’s relationships. While considerably bigger than its close relatives, Sinocalliopteryx was a compsognathid–a group of theropod dinosaurs that also includes fuzzy forms such as Sinosauropteryx and Juravenator. Big or small, the compsognathids were hunters wrapped in wispy plumage.
And the initial description of Sinocalliopteryx mentioned something else. The skeleton that formed the basis of the original paper contained the leg of an unidentified dromaeosaurid dinosaur in its gut contents. Even though dromaeosaurids have long been cherished as sickle-clawed uber-predators, Sinocalliopteryx had clearly eaten the drumstick of one of the smaller feathered predators. Since then, paleontologists have identified a second Sinocalliopteryx with gut contents, and the two dinosaurs form the basis of a new PLoS One study by University of Alberta paleontologist Lida Xing and colleagues.
Looking back at the first Sinocalliopteryx, Xing and colleagues identified the victim as Sinosauropteryx. The second Sinocalliopteryx specimen had a different menu before it perished–its stomach contains the remains of two Confuciusornis, an archaic bird, and bones from an unidentified ornithischian dinosaur. But these gut contents invoke an aggravating mystery. Did these Sinocalliopteryx hunt their dinosaurian prey, or did they scavenge their meals?
This isn’t the first time paleontologists have puzzled over the meaning of predatory dinosaur gut contents. Earlier this year, Dave Hone and collaborators investigated a pterosaur bone found inside a Velociraptor, and last year Jingmai O’Connor and colleagues described a Microraptor with the remains of a bird in its gut (just to pick two examples of many). Frustratingly, though, it’s difficult to say how the dinosaurs obtained the meat. In the case of the Velociraptor, the researchers could not rule out hunting even though scavenging seemed the more likely option. Likewise, even though O’Connor and co-authors suggested their Microraptor hunted birds in the trees, the non-avian dinosaur could have just as easily scavenged a dead bird that fell to the forest floor. Gut contents tell us about what dinosaurs consumed, but they almost never provide direct evidence of how carnivores obtained flesh and bone to eat.
In the case of Sinocalliopteryx, the PLoS One study concludes that the dinosaur may have been skilled at catching live avian prey. The fact that one Sinocalliopteryx fed on two Confuciusornis in quick succession could mean that the large dinosaur was adept at nabbing early birds. “[T]he evidence of bird predation in Sinocalliopteryx,” Xing and colleagues conclude, “suggests that it was a highly capable stealth hunter.” Then again, the same researchers also note that their scenario “is speculative.” While it may seem improbable, the Sinocalliopteryx in question could have scavenged one or both of those birds, as well as the non-avian dinosaur remains in its stomach. We just don’t know. Like many predators, Sinocalliopteryx most likely hunted live prey and took advantage of carrion. Frustratingly, these fossil gut contents can’t tell us what happened in each case. Sinocalliopteryx may very well have been a skilled bird-slayer. Or perhaps not. The fact is that we don’t know for sure.
Perplexing feeding habits aside, there’s something else about the gut contents of Sinocalliopteryx that can give us a closer look at the dinosaur’s biology. In the dinosaur that ate the two birds and the ornithischian, the bone of the ornithischian dinosaur was corroded by stomach acid. The more delicate bird bones, by contrast, had not been so damaged. This means that the Sinocalliopteryx ate the ornithischian first, followed by one bird and, later, another. More than that, the acid damage indicates that at least some dinosaurs had highly-acidic foreguts where bone was broken down–comparable, but not exactly like, the stomachs of crocodilians and perhaps some bone-eating birds like the bearded vulture.
All of which is to say that Sinocalliopteryx is a great example of a fluffy dinosaur you wouldn’t want to mess with. Even if we can’t discern the backstory of each meaty morsel, the variety of prey in the Sinocalliopteryx stomachs shows that this dinosaur wasn’t a picky eater and may have even been a quick hunter that specializing in snapping up other feathery dinosaurs. For our fuzzy mammalian predecessors, hiding the Cretaceous forests, this would have been one scary dinosaur.
Xing L, Bell PR, Persons WS IV, Ji S, Miyashita T, et al. (2012) Abdominal Contents from Two Large Early Cretaceous Compsognathids (Dinosauria: Theropoda) Demonstrate Feeding on Confuciusornithids and Dromaeosaurids. PLoS ONE 7(8): e44012. doi:10.1371/journal.pone.0044012