National Geographic

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.

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

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.

There are 21 Comments. Add Yours.

  1. Shannon Hubbell
    July 16, 2013

    What is Horner’s reputation generally like among other paleontologists? As a layman, saying something “just to be contrary and get my colleagues arguing” seems really irresponsible.

  2. Zach Miller
    July 16, 2013

    Horner’s not helping, either. Instead of bowing out gracefully and acknowledging the science that overturns his pet theory, he’s being apathetic about the whole deal, like it doesn’t even matter. And I wasn’t aware of his “Complete T.rex” quote. That’s…disheartening.

    It’s sad because Jack Horner was, at one point, one of my favorite people on the planet. I watched that PBS “Dinosaur!” show all the time (we had it on tape) and marveled whenever he came on-screen. But as the years have passed, I’ve come to see him more as a cranky obstructionist who’s set in his ways and not all that interested in changing his mind about things.

  3. ian
    July 17, 2013

    Most carnivores are opportunists that will scavange or hunt at different times. Crocs will hunt anything from fish to large mammals, and happily scavange too. As will Lions, and Hyenas etc, just about all predators do so to different degrees. I don’t see why T. Rex would have been any different.

  4. chris y
    July 17, 2013

    For that matter there aren’t that many obligate scavengers either, which will refuse to help on its way a sick prey animal or an isolated juvenile. To paraphrase Wittgenstein, if a lion or a hyaena could talk, it wouldn’t understand the distinction.

  5. Henrique Niza
    July 17, 2013

    Like Brian Switek have rightly said so there isn’t a controversy in the actual field. It was a legit point Jack Horner raised at that time – why assume T. rex was a predator? That isn’t how science works.
    I would recommend watching this ’98 interview with Jack Horner to get what his point was exactly: http://www.c-spanvideo.org/program/111009-1

  6. Thomas R. Holtz, Jr.
    July 17, 2013

    Shannon, Jack Horner is extremely well-respected by the rest of us professional paleontologists. He has, and continues to make, extremely significant contributions to the field.

    Science isn’t about being right all the time; it is about asking questions and finding some method to answer them.

    All of us in Science have proposed ideas that with later data turned out to be incorrect: for example, Horner’s 1980s idea that lambeosaurines and hadrosaurines were not each other’s closest relatives, my own 1990s idea that tyrannosaurids and ornithomimosaurs WERE each other’s closest relatives, and so forth.

  7. Mike Huggins
    July 17, 2013

    Brian: Your take is Interesting when you consider how NatGeo handles this on their news site, which seems like just more controversy-stoking:
    http://news.nationalgeographic.com/news/2013/07/130715-tyrannosaurus-rex-predator-duckbill-dinosaurs-paleontology-science/

    “Horner offered his own speculative scenario for what might have happened: ‘A T. rex could have walked up to a sleeping duckbill dinosaur and bit it, realized it was alive, and then backed away,’ he said. ‘That’s just as plausible as saying that it’s chasing it because there’s no evidence for either one.’ “

  8. Mike from Ottawa
    July 17, 2013

    There’s a difference between advancing an idea in good faith, particularly in the scientific literature where it can be examined properly, and having it turn out to be wrong on the one hand and on the other making mischief creating a bogus controversy where none actually exists. The public pays little enough attention to science without having its attention wasted on a manufactured argument.

    And saying things you don’t really believe just to stir up argument is not exactly something that builds trust and public trust of science is not a trivial thing.

  9. Doug
    July 17, 2013

    I’m kind of in the same camp as Zach. When i was a little kid Horner was one of the rock stars i looked up to. But as time wore on, he began to come off as more crotchety then sciencey (of course i never met the guy. I’m sure he’s a totally different person than the public image he has built).

    While the media has certainly zombified the “controversy”, it can be argued that the whole mess was artificial from the get go, started because someone wanted to be contrarian. Someone on facebook said they talked to Horner about it like 10 years ago and Horner said he had to run with it because of how it took off. But again, hard to say since i’m getting info from sources other than a face to face with the man himself. But i find myself wondering: So Jack, was saying T. rex was an obligate scavenger so you can “… sometimes just to be contrary and get my colleagues arguing.” worth getting dragged through the mud for 20 years?

  10. SP
    July 18, 2013

    Brian — I was at the Brussels (Belgium) natural history museam last Sunday watching a video next to the T.Rex exhibit of Jack Horner explaining to camera that T.Rex was not a predator. So without doubting that there is no academic debate, it is perhaps a little harsh to blame the media alone for the continued confusion.

  11. MPG
    July 18, 2013

    Horner once dropped by a site I was helping with in the Bridger Basin in Montana. Flew in on camera-mounted helicopter, landed, walked around, re-boarded, left. Never said a word to anyone. Not the volunteers, not me, and not the PI for the site. Nobody. It was surreal.

  12. Jonny O
    July 19, 2013

    Jeezuss! Amazed at how no one ever considers the paleo-ecology of these animals in tandem with their morphology. You must remember: these animals were living/evolved in a super-greenhouse. What does this mean??? “FOOD WAS EVERYWHERE” The herbivores had only to express their dietary preferences and the vegetative world responded (such distinctions were the subject of discussion last week!). Well guess what: in the Late Cretaceous world, meat was there for the asking. Plenty of dinosaur carcasses on the landscape meant T-Rex only had to find the most recent dead dinosaur in order to enjoy a fulfilling meal. Think about it: plenty of dino carcasses the size of a modern whale across the landscape. Dead meat was hardly a rare commodity. Seriously, I think the meat-eaters of the Late Cretaceous were some of the laziest predators ever to appear on this planet: in THAT kind of heat, do you honestly think animals want to be frisky and frolicky?

  13. Malcolm Ritter
    July 19, 2013

    May I just point out that not all of us journalists bought into the `ongoing controversy’ angle? Here’s how I wrote the story for The Associated Press: http://bigstory.ap.org/article/bitten-hungry-t-rex-dinosaur-got-away

  14. Doug
    July 19, 2013

    Jonny O- just, just, *facepalm*…

  15. jonny O
    August 9, 2013

    @Doug: sorry, but too many eager dino-philes want these “ruling reptiles” to conform to contemporary mammalian behavioral standards. As one paleo-ecologist put it, the super greenhouse of the Late Cretaceous allowed for more trophic levels than we have today. So-called “food-webs” had more dimensions than we are aware of today. Again, think of it: all those dead dinosaurs. They didn’t just wait for burial in the steaming heat; those carcasses were a bounty of food for the asking. Why waste your time chasing something that runs away from you when you can stuff your gut with a rotting ceratopsian or hadrosaur or even a sauropod?

  16. Brian Edwards
    August 21, 2013

    I blame the likes of Rudyard Kipling who characterise scavengers as cowardly and lowly creatures whilst the predators are all “noble” except the man-eater Shere Kahn who is a “cripple” and therefore must be evil.
    Aren’t almost all predators also scavengers if the opportunity presents?

  17. Noah Eckenrode
    September 15, 2013

    @jonny O: The problem with this argument is that pure scavengers like vultures can fly and cover large areas in search of carrion without expending much energy. T-rex couldn’t fly and if it tried to look for carrion over long distances, it would expend alot of energy. So, if it was a pure scavenger, it would have to wait for something to die within walking distance. But, that wouldn’t happen every day and a body like a T-rex’s needs alot of food to keep going.

  18. Ruben Fernandez
    September 24, 2013

    Jonny O, you have absolutely no scientific proof to back up your statements. Shooting your mouth of with expressions like “Jeezuss!” actually make it worse because you are assuming that logic equals science, and it doesn’t.

  19. D. Shuman
    December 1, 2013

    What disturbs me more than anything else about this non-debate is summed up by two phrases in your opening paragraph: “mighty” hunter or “lowly” scavenger. We superimpose our irrational and value-laden characterizations on the natural world, and they have nothing to do with reality. Scavengers get short shrift, but their place in the food chain is a vital one that would be sorely missed if it were absent.

  20. Marcos K. Pinheiro
    January 7, 2014

    When I learned about this in around 2010, I know I was late, I feared that in the end will see T. rex as an obligate scavenger. But as far as I researched in blogs, news, books and documentaries such as The Truth About Killer Dinosaurs from BBC, I now have a strong defensive opinion that T. rex was more of a hunter than scavenger! Besides, new specimens of Edmontosaurus are revealing more signs of its predatory behaviour, like the one with a scar and the one with a tooth embedded on the tail vertebra yet it healed with it! And there’s even a Triceratops that lost its horn and got bitten marks on its frill which were healed! Even if we don’t know who was the real aggressor, somehow it happened! I found this link and I hope you can aechieve it to read it and see more what paleontologists such as Tanke and Currie said about it.

    http://books.google.com.br/books?id=5WH9RnfKco4C&pg=PA355&lpg=PA355&dq=An+analysis+of+predator-prey+behavior+in+a+head-to-head+encounter+between+Tyrannosaurus+rex+and+Triceratops&source=bl&ots=06bRR21KIv&sig=-kWQomvraxkFgENqUEBCKQLmEtc&hl=pt-BR&sa=X&ei=Xay8UuCoIdDvoATTwIDQDQ&ved=0CDcQ6AEwAQ#v=onepage&q&f=false

    In this link, I’ve learned there are specimens of bite marks in the neck and head regions on Edmontosauruses! Why would a T. rex begins in the head to eat a carrion? Maybe it wasn’t a carrion, it might’ve been a prey that was caught by surprise (since adult T. rex probably wasn’t fast runners and neither faster than these duckbills at least) in the head or neck and could no longer escape from T. rex’s mighty crushing jaws! In my opinion, I believe this Edmontosaurus was really killed as live prey!

    But keep in mind that I respect Jack Horner, he’s one of the greatest hunters of “tyrant specimens in the world” (he found MOR 008, MOR 555 and many others) some of his facts about Tyrannosaurs are right, but the facts like the tooth decreasing as they grew and they were obligate scavengers when adults I disagree.

    Thanks to these links:

    http://www.bioone.org/doi/abs/10.1080/02724634.2011.557116

    http://www.tandfonline.com/doi/abs/10.1080/02724634.2011.557116#.UswqQbR8C2o

    And thanks to Switek’s “paleo-opinions”, in fact, to me he has become one of the greatest dinosaur experts that I can trust most, because (please don’t be modest) I believe that you look for the truth and more unspoked finds and paleontological evidences that he always surprises me! Like this and other blogs about “T. rex as both hunter and scavenger”. He’s inteligent and he’s always helping the dino fans to change or learnd more about the creatures of Mesozoic, not just T. rex! I, and always will, believe that the “king of all the tyrants of Mesozoic” was a magnificent coelurosaur than some people give credits for! And so were its tyrannosaur cousins like Dilong, Gorgosaurus and Eotyrannus!

  21. Chris
    September 5, 2014

    Johnny O,
    You fail to take into account that the herbivores had evolved physical traits to counter predation. The carnivores didn’t sit around waiting for animals to die, they made it happen.

    As for Horner’s flippant remark that the hadrosaur(?) with the embedded tooth could have been asleep. A T-rex stumbles upon a sleeping herbivore and starts dinner at the tail? That makes no sense.

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