Tyrannosaurus rex Is Done Answering Questions About Its Diet

The state of the universe.
July 17 2013 1:00 PM

Stop Asking Tyrannosaurus Rex About Its Diet

Can’t a carnivorous dinosaur just eat whatever it wants to?

Dinosaur Sue, the largest intact Tyrannosaurus Rex specimen yet discovered, is prepared for display at the Dinosaur Expo at the National Science Museum in Tokyo, Japan, March 14, 2005.
Dinosaur Sue, the largest intact Tyrannosaurus Rex specimen yet discovered.

Photo By Toshifumi Kitamura/AFP/Getty Images

This week I encountered the question that, as a scientist who has studied a certain chunky Cretaceous carnivore a lot, most deflates me and makes me want to go study cancer therapeutic methods or energy sources that are alternatives to fossil fuels (but I’d be useless at either). I will explain why this is at the end of the post.

The question is whether Tyrannosaurus rex was a predator or a scavenger. It stems from a new discovery reported in the Proceedings of the National Academy of Sciences and thus expected to be one of the more important or exciting studies this year. (No, I’m not going to get into the issue here of whether these “high impact” journals include the best scientific research or the most superficial or hyped “tabloid” science; they publish both, and not in mutual exclusivity.) It’s a broken Tyrannosaurus rex tooth embedded in a duckbill dinosaur’s tail bone, which healed after the injury, showing that the animal survived the attack.

If you’re with me so far, you might be making the logical leap that this fossil find is then linked to the hotbed of furious controversy that still leaves paleontology in crisis almost 100 years after the paleontologist Lawrence Lambe suggested it for the tyrannosaur Gorgosaurus. If the hadrosaur survived an attack from a T. rex, then T. rex was a habitual predator and OMG Jack Horner and others before him were wrong!

And you’d be right.

My encounter with the question stemmed from an email from a science journalist, Matt Kaplan, who, as is normal practice, shared a copy of the unpublished paper and asked for comments from me to potentially use in an article he was writing for the science journal Nature’s news site. Here, then, was my off-the-cuff response:

“Ooh. I do have a pretty strong opinion on this. Not sure if you’d want to use it but here goes. I may regret it, but this hits my hot buttons for One of the Worst Questions in All of Paleobiology!

The T. rex ’predator vs. scavenger‘ so-called controversy has sadly distracted the public from vastly more important, real controversies in paleontology since it was most strongly voiced by Dr. Jack Horner in the 1990s. I find this very unfortunate. It is not like scientists sit around scratching their heads in befuddlement over the question, or debate it endlessly in scientific meetings. Virtually any paleontologist who knows about the biology of extant meat-eaters and the fossil evidence of Late Cretaceous dinosaurs accepts that T. rex was both a predator and scavenger; it was a carnivore like virtually any other kind that has ever been known to exist.

While the discovery is nice evidence, it is not particularly exciting in a scientific sense and is only one isolated element from species that lived for hundreds of thousands of years, which to me changes nothing and allows no generalizations about the biology of any species, only the statement that at one point in time a Tyrannosaurus bit a hadrosaur that survived the encounter. There is no real substance to the controversy that T. rex was ’either‘ a predator or scavenger. It is just something that scientists drum up now and then to get media attention. I hope that soon we can move on to more pressing questions about the biology of extinct animals, but the media needs to recognize that this is just hype and they are being played in a rather foolish way; likewise scientists who still feel this is an exciting question need to move on. Maybe this specimen will allow that. But somehow my cynical side leads me to suspect that this ’controversy‘ will just persist because people want it to, regardless of logic or evidence.

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 paleontology is so much better than this.

Sorry for the rant. Maybe it’s too extreme, but I’m just fed up with this non-issue! I suspect a huge proportion of our field feels similarly, however.”

(I later redacted a bit of it where I got a little too excited and used the word curmudgeon; a mistake, as that could be seen as ad hominem rather than a term of endearment, and this issue is about the science and not the people, per se. That bit is redacted here, too. I’ve also redacted a sentence in which I made an opinion on whether the paper should have been published in PNAS; that is mostly irrelevant here. I was not a reviewer, and authors/reviewers/editors have to make that decision. This would be a massive tangent away from what this post is intended to be about! I know some of the authors and don’t want to offend them, but this is about the science and how it is represented to the world, not about these particular authors or even this paper itself.)

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Importantly, Kaplan’s story did include my skeptical quote at the end. I am curious to see how many other news stories covering this paper go that far. [Ed. note—Embarrassingly, a Slate Trending News Channel video did not.]

I will stop right here and acknowledge that I’ve published a lot on a somewhat related topic: how fast a T. rex could run or whether it could run at all. To me, that’s a great scientific question that has consequences not only for the predator/scavenger false dichotomy, but also for general theories of locomotor biomechanics. (Can an animal the size of a large elephant run as well as or better than said elephant? What are the thresholds of size and maximal running/jumping/other athletic abilities and how do they vary in different evolutionary lineages? And so on.) I’ll defend the validity of that question to the bitter end, even if it’s a question I’ve grown a little (but only a little) tired of and generally feel is about as well settled as these things can be in paleontology (see my review here). I’ll also defend that it has been a real controversy (I have plenty of old emails, formal rebuttals submitted by colleagues, and other discourse as evidence of this) since I tackled it starting in 2002 and sort of finishing by 2011. I am sensitive about the issue of hyping my research—this is something I’ve been careful about. I set a reasonable bar of how much is too much, check myself continuously with reflective thought, and I do not feel I have ever really crossed that bar, away from science-promotion into darker realms. This is partly why I’ve stopped addressing this issue in my current work. I feel like the science we’ve done on this is enough for now, and to keep beating the same drum would be excessive, unless we discovered a surprising new way to address the questions better, or a very different and more compelling answer to them.

T. rex: scavenger or predator?” was controversial back in 1994 when Horner published The Complete T. rex, where he laid out his arguments that T. rex was a scavenger. Brian Switek covered this quite well in his post on it, so I will not review that history. There was a big Museum of the Rockies exhibit about it that toured the United States, and other media attention surrounding it, so Horner’s name became attached to the idea as a result. Other such as Lawrence Lambe and Paul Colinvaux had addressed it before, but their ideas never seemed to gain as much currency as Horner’s did. But this post is not about that.

What this post is about is a consideration of why this is still an issue that the media report on (and scientists publish on; the two are synergistic of course), since most scientists aware of past debates are in good agreement that a T. rex was like most other carnivores. It was opportunistic as a switch-hitting scavenger-predator, not a remarkably stupid animal that would turn down a proper meal depending on whether it was dead or alive. Indeed, the Nature news piece has a juicy quote from Horner that implies (although I do not know if it was edited or if important context is missing) that he has been in favor of the opportunistic predator-scavenger conclusion for some time. Thus, as Switek’s article notes, even the strongest advocates of the obligate scavenger hypothesis have changed their minds; indeed, that 2011 blog post intimates that this had already happened at least two years ago.

For many years, nothing has been published in the main peer-reviewed literature that favors that extreme obligate scavenger hypothesis. If I am wrong and there is a scientific debate, where are the recent papers (say within the past five years) that are strong, respectable arguments in favor of it? I contend that it is a dead issue. And if it is just about the middle ground—i.e. what percent of its time did a T. rex spend hunting vs. scavenging—we have no clue and may never know, and it’s not a very interesting question. Yes, the new find is a neat fossil. But a different duckbill dinosaur specimen in Denver whose tail a tyrannosaur had reputedly taken a bite out of has been known of for over 15 years , so the novelty of this new specimen is questionable.