by Carlos Augusto Chamarelli
Hey there again. After the previous article about Jack Horner’s plan to transform chickens into dinosaurs, what’s better than go back to showing contempt for his other theories? So let’s talk about his opinions regarding that one elusive theropod nobody ever heard about: the Tyrannosaurus rex.
Most specifically, about the most heinous and debated of his claims: that T.rex was so ill-suited to be a hunter that he had to live entirely of kills from other predators and was no more than a giant vulture. Understandably not many people were happy with this, and many studies since were made to verify if Horner’s claim were true. With mixed results, but not that stopped some to agree with him.
In reality he wasn’t the first to try and discredit T.rex of his predator status; back in 1917, paleontologist Lawrence Lambe concluded Tyrannosaurus couldn’t be a predator because Albertosaurus (yeah, I don’t know either) teeth did not show any sign of wear, which soon enough was pointed out as BS because theropods constantly changed their teeth throughout their lives. So T.rex continued to enjoy his status as the supreme predator he’s cracked to be and the scavenger theory was mostly left aside.
I’m not sure when Horner first proposed T.rex was a scavenger, but his opinions were already present during the early 90’s; during the production of Jurassic Park, in which he was one of the paleontological consulters, he stated that T.rex should be depicted as such. Fortunately, everybody knew better and made him a hunter like Bakker suggested, and we could see the creature in all his glory in the first two movies of the series.
Until the early 2000’s that is, when Horner’s theory came in full power to the public. His TV-special “Valley of the T.rex” was entirely devoted to show the creature as a stinky scavenger, and during the production of Jurassic Park 3, Bakker knew better than participate of this train wreck, leaving the movie at the mercy of Horner as its sole consulter…
As Wikipedia so nicely resumes for us, the main aspects that Horner uses to rationalize the idea of T.rex as a scavenger are as follow:
– Tyrannosaur arms are short when compared to other known predators. Horner argues that the arms were too short to make the necessary gripping force to hold on to prey.
– Tyrannosaurs had large olfactory bulbs and olfactory nerves (relative to their brain size). These suggest a highly developed sense of smell which could sniff out carcasses over great distances, as modern vultures do.
– Tyrannosaur teeth could crush bone, and therefore could extract as much food (bone marrow) as possible from carcass remnants, usually the least nutritious parts.
– Since at least some of Tyrannosaurus’s potential prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger.
That said; let’s take a closer look at each of these points, shall we?
Ah yes, T.rex arms. Those sorry excuses for limbs are the trademark of the king and his kin. Completely out of proportion and with only two fingers, it’s easily one of its most puzzling characteristics as many theories and no agreement exist about their real utility; ranging from a prosaic, moderately believable but ultimately flawed use like lifting his body when the animal was lying down, to the most reason defying such as picking his teeth or holding struggling prey.
But I do believe the answer is in fact quite simple, but lots of people will be outraged exactly because of that.
T.rex most likely didn’t use them for anything because, well, it didn’t need. They were in a process of atrophy*. It’s really sad that the only mention of such occurrence is usually attributed to the outdated theory of Lamarckism, with the law of use and disuse, because, in a way, that’s kind of what happens.
To understand it better: you know that evolution work by mutations, right? They occur at random in the process of reproduction, but as the model always goes, if said mutation proves to be an advantage for that individual, he has higher chances to pass on his genes for the next generations. But sometimes, things go in a different direction.
Let’s make this one model with two different species, a caveman and a T.rex.
The caveman is like your average caveman: he has two legs, two arms, a head and a big, spiked club. The T.rex, on the other hand, is actually an ancestor form which have long arms, fictionalized for the sake of the explanation**, he’s like “cool, I can grab things with these, but my mouth already does everything I guess”.
Now say that they both at some point had offspring with mutations that affect their forelimbs, making their arms dwindle and become useless. For the cavemen, this could be fatal since he relies on his hands to grab things, make tools, maybe even socializing, so the natural conclusion is that this bad gene results in a dead caveman who never stood a chance to have children. For the T.rex, his tiny arms doesn’t affect him as much, because his jaws do all the work of killing prey and fighting rivals, which means he can survive normally and pass on his “bad” genes and create an entire dynasty of short-armed dinosaurs.
In other words, if a mutation doesn’t have a big impact in the creature’s lifestyle, it probably will carry on to next generations until the whole species has it. Among some examples where this happened we can cite snakes and other legless reptiles (which became, you guessed it, legless), primitive tetrapods (which lost fish characteristics such as fins) and even us humans (which lost our tails).
Degenerated arms are not even an exclusivity of tyrannosaurids; other dinosaurs had similar occurrences, from the small, one-fingered alvarezsaurids such as Linhenykus (whose arms were more like pointed stubs) to giant Abelisaurids, the “T.rexes of the south hemisphere”, so to speak. The latter, in fact, had much more pathetic-looking limbs than T.rex.
There were also the famous terror birds, which appeared in the Cenozoic; these too were large-sized predators with beaks as deadly as their wings where shamefully small. The logical conclusion with all of this is that arms for bipedal predator dinosaurs are overrated, and the fact T.rex had tiny arms as he did is completely irrelevant as evidence for scavenging habits.
Remember that one scene in Jurassic Park where the T.rex escapes and Grant has to save Hammond’s grandchildren and they stand perfectly still because then the T.rex couldn’t see them? Of course you do, you read about it everywhere how it’s bonkers because he could have smelled them: T.rex had an exceptional sense of smell, just one more of his claims to fame.
T.rex’s sense of smell is thought to be surpassed only by the modern day turkey vulture (Cathartes aura), which is all too convenient to Horner’s theory, right? Except having a good sense of smell is just as useful for hunting animals, as proved by modern canids and felines. “But, PK, those are mammals, we’re talking about dinosaurs! They’re closer to birds!” you might say, but that’s alright, because contrary to what many might believe thanks to the super-sniffing vultures, some non-scavenger birds do have a good sense of smell.
The majority of them use it to detect predators, but there are some species that use it to hunt prey, like the kiwi birds, whose nostrils are so long they actually go all the way to the tip of the beak, excellent for sniffing worms underground.
But even more bonkerous is the fact that, never mind his extraordinary olfaction, he COULD see them!
It’s not always apparent, because most of the time you see pictures of T.rex’s skull in profile, but if you have the chance to look at one from the front, you’ll see that the hind part of the skull is actually visibly wider than the snout, causing the eyes to face forward rather than the sides as it’s more commonly seen in dinosaurs; it’s also at a higher level than the snout, giving it a clearer view and the distinctive shape.
Eyes facing forward are a characteristic of animals with good eyesight, such as primates and birds of prey, with the owls being the ultimate example of this; the binocular vision provided is essential for calculating distances better and maintain focused on targets. So that’s a tricky question: if T.rex was a purely a scavenger, then why did it had eyesight akin to predatory birds who are such efficient hunters?
– Teeth and jaws
Tyrannosaurids are an interesting lot when it comes to teeth. Usually, carnivore dinosaurs have slicing teeth shaped like steak knives, efficiently tearing the flesh out of the victim’s bone. T.rex, on the other had, had teeth at one point described as “deadly bananas”: they where thick and with very deep roots, which made them incredibly strong.
In addition, their jaws were also different: the classic model has the jaws roughly the same width; while in T.rex the upper jaw was wider, giving him the characteristic overbite appearance, which allowed him to stress bones in such a way that they could easily crack them.
On top of that, T.rex is thought to have had the most powerful bite in the dinosaur world. How powerful it was? The most recent study, released this year, indicates around 30,000 and 60,000 Newtons. To puts things in perspective, the previous study pointed up to 13,000 Newtons, enough to crush a car. That being said, I’m not surprised if someone told me that if a T.rex and a tank were in a fight, the dinosaur would’ve won.
But once again, this isn’t an indicative that T.rex was purely a scavenger, since powerful bites aren’t unique to such behavior. Think of the jaguar (Panthera onca), which isn’t one of the largest big cats out there, but even for its size it has an unusually strong bite that can crack even a man’s skull, and is the apex predator of its habitat.
Hypothetically speaking, if jaguars were to evolve into much larger species, then forms with even stronger bite power could appear. For a creature as big as T.rex, this could be one such scenario; their ancestors could be like the jaguar in size and potency, but things went out of hand and produced a big animal with an insanely strong bite, and being able to feed on bone marrow was just an appreciated bonus.
So anyways, remember that scene in Jurassic Park 3? Yes, THAT scene…
IT WAS TOTAL BS!
The first bite to the neck would’ve been enough to kill the Spinosaurus. See, that’s one reason that makes T.rex lives up to its title: it doesn’t matter if Spinosaurus or Giganotosaurus or any other theropod was larger than him, his absurdly powerful bite would be more than able to overpower them.
But no, Horner had to have things his way and cheated by okaying them into making a Spinosaurus on steroids not care about fish and fight a sub-adult T.rex and survive a bone-crushing bite to the neck. Sorry about that little rant, but it’s all just too unnerving to see such gratuitous mockery of paleontology in one place.
– Legs and body build
Paleontologists have divergent opinions about the overall build of Tyrannosaurus; two body models commonly followed are the bulky type and the athletic type. The bulky body implies a slow-moving creature with a more limited ability to run, some might say one that would be unable to chase its prey, while the athletic body implies an active running creature.
Paleontologists who support the athletic type suggest that, despite it’s size, the overall proportion of the legs of the T.rex are more characteristic of a running animal, in other words, T.rex was very much able to catch up with its prey in a chase. So naturally this is what makes the most sense if you want to show T.rex as a hunter.
My opinion? He was a bulky type.
In reality, nobody is quite sure of how fast Tyrannosaurus was, but from analysis and calculations an estimative can be made, but even those don’t really support the image of T.rex running at overly high speeds as usually shown.
In a optimistic scenario, the top speed for T.rex is somewhere around 30 km/h (18 mph) at best, which isn’t terribly fast. I’ve read about some estimatives being over twice this value, but that seems more like an exaggeration to argue with Horner’s theory in the wrong direction.
Because the larger the creature becomes, the more heavily built it has to be in order to support its own weight, there’s a limit on how light the creature can be until it become too big and heavy to support itself, so a large bipedal creature like T.rex probably needed to have a solid build in order to stand in their feet. Not to mention that, in order to be able to run at the suggested exaggerated speeds, much of its body mass would have to be in their legs muscles.
Whoever, being slow doesn’t rule out the possibility of Tyrannosaurus being a hunter; he maybe just had a different approach. Instead of focusing in speed, Tyrannosaurus could be a robust creature built primarily for strength. Why would did he need to be so? Well, what manner of prey did he had available in his domain?
Why, just the most dangerous herbivores ever to appear in the Mesozoic era.
Nobody can attribute speed as a quality of ankylosaurids; they had a solid build, covered in heavy armor and short legs for better standing their ground.
Ceratopsians, despite what most reconstructions tend to show, were probably very poor runners: their forelimbs weren’t even appropriate to run, (I intend to talk about this in a future post) so they probably relied more in numbers and their own weaponry for survival than making a dash for it. So if being fast wasn’t needed to catch its prey, the best option would build up endurance, and the apparent running legs of T.rex would be more like a way to trade speed for strength without being completely handicapped.
Meaning the T.rex wasn’t a creature made to pursue its prey. No sir. He was juggernaut made to stay there and fight them, and win. Somehow pure raw strength could prove to be a better strategy than speed to overcome a well armed opponent.
While the T.rex could be injured or even killed by his prey, he could also finish it just as easily: biting the head or the backs would have shattered their bones and leave the prey paralyzed in the best of hypothesis, while just ripping a chunk could leave a fatal wound. In this scenario, T.rex’s eyes would then be an invaluable asset to focus on their prey during the fight, rather than be used during a chase. And if he ever needed to run, it would be more like walking real fast.
In a way, one can think that ceratopsians and ankylosaurus where in a mutual armed race with tyrannosaurids, each developing even more powerful weapons against each other: they seemed to be found primary where those types of herbivores thrived (i.e. North America and Asia), and their evolution is somewhat consistent with the appearance and ascension of those herbivores. Now consider this: despite the duckbilled dinosaur’s fame as widespread, they were actually outnumbered by ceratopsians, which means something must have been preying on them to keep their numbers, right?
Oc course, that’s my personal opinion, I might be wrong: there’s no evidence of ankylosaurids with signs of predation yet, but I’m not convinced absolutely nothing would attack them if given the chance, specially something with a bite like T.rex.
While there’s evidence that T.rex preyed on both hadrosaurids and ceratopsians (i.e. some show teeth perforations while others healed bite marks in bones that could only be possible if the dinosaur was alive), it’s safe to assume that the horned dinosaurs were his chief prey, at least to the fully mature individuals.
While there’s no official estimative on how fast hadrosaurids could run, it’s certain that they were faster than an adult T.rex, but if it’s true that they could also hunt in packs to a degree, then it could be an explanation for this finding. Alternatively, younger individuals could have preyed on hadrosaurids if they were light built. But even more impressive seem to be the fact that something actually could survive an T-rex attack.
Actually yes, there’s one more point beyond the ones listed: Energy efficiency.
Modern scavengers like vultures and jackals are allowed the luxury having this lifestyle because they’re small and can cover a large area without wasting too much energy (i.e. vultures are soaring birds, meaning they are able to maintain flight without flapping their wings).
A large creature like T.rex would be doomed to extinction if it was an obliged scavenger because he would probably run out of energy trying to locate the next meal, and even then he has to hope there’s enough left to eat and no other T.rex claimed it already, not to mention this unviable lifestyle would make their population be massively reduced in order to be able to support just a handful of these dinosaurs
So there you have it. Tyrannosaurus might not have been the largest carnivore to ever exist, but he certainly was the most powerful. Despite all those evidences, there’s a consensus among those who support the hunting behavior of T.rex that he was an opportunistic hunter. That is, while he could very well kill his own prey, he wasn’t above stealing or eating carcasses. It’s a free meal after all.
In the end, this is what the whole problem is about: Horner didn’t take in account that the evidence he used to support his theory also had explanations that indicated the opposite. Just to make things clear with the “Why I Don’t Trust Jack Horner” series: while I don’t think he’s a bad paleontologist, I do believe he’s a little misguided about his recent theories. And quite frankly, I’m pretty sure that if Horner went back in time and was face-to-face with the creature he’s sure was a scavenger, he would NOT just stand there calmly.
Thanks for reading!
* Because once the first degeneration took place, nothing would stop it from being further degenerated by a subsequent mutation.
** Early tyrannosaurids did have longer arms, but in the model the dinosaur is already in its later form to illustrate that even a sudden mutation, as opposed to a gradual one, still wouldn’t affect it.
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References & Further Reading:
Erickson, Gregory M. 2005. ‘Um Sopro de Vida no Tyrannosaurus rex’. Scientific American Brasil – Edição Especial: Dinossauros e Outros Monstros.
Wikipedia. Tyrannosaurus. Available on-line in: <en.wikipedia.org/wiki/Tyrannosaurus>. Acess on May 15th, 2012
BBC – T. rex bite was world’s strongest. Avaiable online at: <http://www.bbc.co.uk/nature/17159086>
Science Daily- Birds Can Detect Predators Using Smell. Avaiable online in: <http://www.sciencedaily.com/releases/2008/04/080427233813.htm>