Photo by Brian Switek
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Tyrannosaurus face off at the Museum of Ancient Life in Lehi, Utah.
Photo by Brian Switek

Time to Slay the T. rex Scavenger “Debate”

Whether I’m on the radio, giving a public talk, or in conversation, one question about dinosaurs follows me almost everywhere I go – was Tyrannosaurus rex a mighty hunter or a lowly scavenger? I try to suppress my immediate urge to roll my eyes and despondently sigh whenever the query turns up. I’m not aggravated by the asker, but by the fact that a twenty year old non-debate has continued to create the impression of genuine controversy. The miscomprehension got another boost in the journal PNAS this week.

The paper in question, composed by Palm Beach Museum of Natural History paleontologist Robert eePalma and coauthors, centers on a damaged tail bones from one of the herbivorous, shovel-beaked hadrosaurs that roamed western North America around 66 million years ago. Tucked inside a rounded, ugly mass of pathological bone fusing two vertebrae is the tip of a tooth from a large carnivorous dinosaur – most likely the infamous T. rex given the anatomy of the tooth and the lack of other large predators in the same geologic formation.

Such damage, dePalma and colleagues rightly conclude, was probably caused by a failed attempt to take down the hadrosaur. The tyrannosaur bit the herbivore’s tail, but the victim wrenched away with such force that a piece of the carnivore’s tooth broke off as the hadrosaur fled. There was enough time between the attack and when the hadrosaur died for the bone to heal, a sure sign of survival. Unlike unhealed tooth marks on bone – common damage that could have been made at a kill or by scavenging – a healed bite wound is a probable sign of predatory behavior. When tyrannosaurs failed, they actually cemented their reputation as hunters. In the paper itself and a spate of news reports, dePalma has touted this the proof that will end the controversy over T. rex feeding habits.

Many museum curators have weird and pathological specimens in their collections, and I’m glad to see this one published. But the damaged dinosaur bone doesn’t resolve the “T. rex as scavenger” issue because there was never any legitimate debate on this point. Our beloved T. rex was undoubtedly a predator and a scavenger, and the ongoing fascination with the dinosaur’s reputation has far more to do with muddled media than science.

Twenty years ago, at the first ever Dino Fest event at Indiana University-Purdue University at Indianapolis, the famous paleontologist Jack Horner stood before a crowd of dinosaur fans to deliver his talk “Steak Knives, Beady Eyes, and Tiny Little Arms (A Portrait of T. rex as a Scavenger).” In his estimation, our favorite dinosaurian carnivore looked like the antithesis of an active predator. Velociraptor – a co-star of T. rex in the first Jurassic Park film that Horner advised – had the long arms and apparent nimbleness required of an active hunter, whereas T. rex seemed to be a plodding giant with a reinforced skull best-suited to crushing and dismembering dead Triceratops and Edmontosaurus. “Picture Tyrannosaurus rex,” Horner told the audience:

He has no arms, can’t run fast, appears to have a large olfactory lobe and he’s big. Interestingly enough if you think about it, one of the best things to be if you are a scavenger is big so you can chase away anything else around the carcass.

Horner continued to noodle around with the idea in his book The Complete T. rex, a book published in 1993 and co-written with Don Lessem. Horner made some allowances that T. rex could have taken down young or sick animals, but, primarily, he cast the dinosaur as a scavenger. And while Horner tipped his hat to earlier paleontologists who had toyed with the idea that tyrannosaurs totally relied on putrefying carcasses to survive, the paleontologist became the spokesman for the contrarian interpretation of the tyrant king’s feeding habits in a slew of documentaries such as Valley of the T-Rex, T-Rex Exposed, and T. Rex: Warrior or Wimp? That’s a lot of airtime for the same idea to be regurgitated over and over, not unlike a bolus of half-digested Triceratops.

Not that even Horner himself took the claims of T. rex as an obligate scavenger seriously. “I’m not convinced that T. rex was only a scavenger,” Horner wrote in The Complete T. rex, “though sometimes I will say so sometimes just to be contrary and get my colleagues arguing.”

Nevertheless, journalists missed the fine print and quickly turned Horner’s contention into boilerplate that could be trotted out to frame almost any new study about the now-embattled dinosaur. From bite force to running speed to dinosaur bones punctured and scored by tyrannosaur teeth, most anything seemed to play into the controversy. Only, there wasn’t a real scientific controversy to discuss.

Horner stated his case in front of museum audiences, in books, and on television. But he never actually did the scientific legwork to support his hypothesis. There was no technical paper or detailed study spilling the particulars of his proposal. Horner had done little more than kick the paleontological hornet’s nest and reaped the media benefits of challenging the reputation of our most cherished dinosaur celebrity.

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Tyrannosaurus menaces at Triceratops at the Natural History Museum of Los Angeles. Photo by Brian Switek.

Other researchers objected to Horner’s characterization from the start. There was nothing about T. rex that would have prevented the toothy and toothsome dinosaur from both hunting and scavenging. Yes, Velociraptor and Tyrannosaurus were anatomically distinct, but it wasn’t as if there was only one way to be a predator in the Mesozoic. These objections seemed to be drowned out by the false argument.

For the popular press and public, Horner’s argument rested entirely on his media prominence. And, ultimately, the few studies that directly considered this media-driven argument were carried out by other researchers. One of the few studies to explicitly discuss the topic suggested that, from an energetic standpoint, there would have been enough carrion in the Hell Creek Formation habitats for T. rex to only eat rotting meat if the dinosaur so chose, yet more recent studiesone of which by the same authors – contradicted this conclusion.

In 2008, tyrannosaur expert Thomas Holtz, Jr. did what Horner never did. Holtz stacked up Horner’s claims about the dinosaur’s anatomy and critically evaluated them. The notion that T. rex was best suited to be a scavenger crumbled. T. rex did not have unusually small eyes; biomechanical studies and limb proportions suggested that the carnivore was quick enough to catch fleeing prey; the dinosaur’s skull was reinforced to the point of being equally capable of subduing struggling prey and dismembering carcasses; and the oft-ridiculed arms of the carnivore would not have prohibited T. rex from employing the shattering power of its jaws.

Holtz’s argument went beyond the theoretical – damaged tail vertebrae on an Edmontosaurus skeleton gave away the depredations of another T. rex who clumsily let their prey escape to live another day. The new paper out this week is a valuable as an additional case, but is more a matter of closing the barn door after the dinosaur is out.

Of course, many journalists can’t resist a T. rex tale, especially when the study claims to settle a controversy about the fearsome titan. Science news sites and tabloids alike smelled the dinosaurian chum and took the bait laid out by the paper.

Journalists have proven themselves to be the true scavengers, with not a hint of hesitation at feeding at putrefying stories that were better buried long ago. In a post reacting to the latest hype, John Hutchinson – who has done a great deal of work on T. rex running speed – perfectly expressed the sentiment so many feel when the obligate scavenger idea raises its gnarly head:

Great galloping lizards, I am so tired of this nonsense. Maybe there is educational value in showing how science deals with provocative half-baked ideas about celebrity species, but scientists in the community need to speak up and say what the real science is about. It’s not about this “controversy”. Modern palaeontology is so much better than this.

Strangest of all, Nature News quoted Jack Horner himself saying that the new study doesn’t change much at all and that – contrary to all the media he helped generate – that T. rex was both a hunter and scavenger. In multiple reports, paleontologists are telling reporters to stop trying to spark a manufactured controversy, and yet the writers ignore the very advice they asked for.

Surely the issue must be dead at this point? Even the paleontologist who pushed the concept for so long has given up on a strict diet of carrion for T. rex. But I wonder whether this exasperated conclusion will seep into the public consciousness.

Journalists and documentary programs pushed a false debate for years, and scientists picked up on the non-issue as perfect bait for inexperienced writers looking for a sensational story. This may be a case of a zombie meme – totally dead as far as experts are concerned, but the traditional angle for the cadre of generalist journalists who don’t have the time or experience to delve deep into details. That’s a sad symptom of the sorry state of science reporting.

I have no doubt that the next time I give a talk or go on the radio, someone is going to ask a question that should have been extinct two decades ago. When they do, I am going to patiently explain how journalists and some attention-seeking scientists are full of coprolite.

[Coda: I composed this post last night. And, as I expected, the question of whether T. rex was a hunter or scavenger came up today while I was on WNPR’s Colin McEnroe Show.]

References:

dePalma, D., Burnham, D., Martin, L., Rothschild, B., Larson, P. 2013. Physical evidence of predatory behavior in Tyrannosaurus rex. PNAS. Online ahead of print.

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

Horner, J., Lessem, D. 1993. The Complete T. rex. New York: Simon & Schuster. pp. 203-220

Horner, J.R. 1994. “Steak Knives, Beady Eyes, and Tiny Little Arms (A Portrait of T. rex as a Scavenger.” in Rosenberg, G.D. and Wolberg, D.L. (eds) Dino Fest. The Paleontological Society Special Publication No. 7.