The Great Predatory Tyrannosaur

Tyrannosaurus Rex was too awesome to be exclusively a scavenger. But no one accepts that as a reason. For me it ends there  However, some believe the mighty t-rex just couldn’t cut it as a predator. Let’s see how it really fared. First I’ll present arguments in favor of it being a predator. Then I will propose rebuttals to the main arguments for why it is a scavenger.

Presenting the arguments for predator:

Argument from expertise
No one believes T-rex was exclusively a predator. Most dinosaur paleontologists believe they were primarily a predator, and may have scavenged when they found meat, much like lions today. However, “Dinosaur Jack” (John Horner) is the only important paleontologist who believes T-rex was exclusively a scavenger. I own and have read his book “The Complete T-rex” in which he argues why (I’ll go into detail about his arguments later as they appear). There’s more prominent scientists who disbelieve in global warming! There’s probably more music industry history experts that believe Elvis is still alive.

Argument from evolution
T-rex lived at the very end of the age of the dinosaurs, during the last part of the Cretaceous. The Jurassic, Triassic and most of the Cretaceous contained plenty of predators. But when the T-rex lived, at the end of the dinosaurs, there were no other predators in the same areas except for very small ones; there were no predators living in the same places who would eat the same size things. For example there was Coelurosaurus which weighed like 200, maybe 300 lbs tops compared to the 5 ton T-rex. A comparison could be like if wherever you find lions, the only other predator you find is one that weighs about 10 lbs or less. Obviously, the lion and the ten pounder will be eating vastly different things. In other words, T-rexes filled every predatory niche larger than "really small." Adolescents ate medium prey, and adults ate the bigger prey. They weren’t just predators, they were so good at it, they out-competed all other predators! And they didn’t just out-compete them, they out-competed them and prevented any other predators from evolving the entire time t-rex was around! It wasn’t until the mass extinction at the end of the Mesozoic - after all dinosaurs were extinct - that predators other than t-rex (and the tiny ostrich ones) again roamed the earth. Nothing but a cataclysm could dethrone the king!
No one contests or disputes that the ancestors of the T-rex (the group is called tyrannosaurids) were predators. Proponents of the idea that T-rex was strictly a scavenger must explain these points:
A) Why, during the final portion of the dinosaur age (Mesozoic) was there suddenly no predators around except ostrich dinosaurs? The excellence of the T-rex as a predator provides the only logical explanation.
B) And why, after all other predators went away, did no other large predator evolve to prey upon the myriad kinds of large herbivores during the last millions of years of the Mesozoic? Again, the excellence of the T-rex as a predator provides the only logical explanation.
C) Why, after the tyrannosaurids were a very successful group of predators, did the final, most powerful one, suddenly evolve to be a scavenger?

Argument from wounds
Dinosaurs have been bitten by T-rexes and survived (a healed tail bone has been found for example), so we know T-rexes bit living herbivores who escaped. This needs no explanation; it would be incredible to believe scavengers bit herbivores without intending to eat them!

Argument from behavior (argument from poop)
T-rexes preferentially ate hadrosaurs (duckbills). We know this from analyzing their fossilized poop. They must have found duckbills easy prey (or just tasty!) because in T-rex poop there are far more bones of them than of triceratops or other contemporary herbivores (triceratopses are deadly with their horns, so this makes sense!). Scavengers eat whatever they find – they never pick and choose what kind of dead flesh, they eat all dead flesh. If T-rex was primarily a predator, the preferential eating makes a lot of sense. The idea that T-rex was a picky scavenger needs a lot of explanation.

Argument from bite
Scientists believe it would be impossible for a t-rex to not have a septic bite. The komodo dragon (and some other lizards) have this feature as well. But since this is a side effect of eating meat, it doesn’t necessarily mean that this feature evolved specifically to kill prey, right? Actually, there were little notches that seem to have been for that very reason – to capture pieces of meat so that the bite would be septic. In other words, it seems that the septic bite – which is utterly useless for a scavenger – was intentional in the design of the teeth. This makes the t-rex a little less cool to me, and even superfluous since the t-rex’s bite was so powerful that 500 lbs of meat could be ripped off (and if that isn’t killing power, what is?). I mean, why do we need the greatest and most powerful ever of all land predators to have venom?

Argument from teeth
“Dinosaur Jack” Horner discovered that they replaced hundreds of teeth per year (much like a crocodilian). Although he believes they were scavengers, in his book he never addresses this issue: why would they need to constantly be growing new teeth if they ate soft, rotting meat? They also had the largest teeth of any carnivorous dinosaur – in fact, they had the largest teeth in proportion to its body (oversized teeth), giving it an advantage over other predators. Why do scavengers need the largest teeth of any carnivorous dinosaur? Indeed, why did the tyrannosaurids, all of whom were predators, suddenly evolve one with even larger teeth, but that doesn’t use them to kill? Why would a scavenger, eating rotting and soft meat, require a constant replenishment of teeth? Using teeth for grabbing and killing prey explains why teeth would be often torn out and lost, but as a scavenger this presents a mystery.

Argument from jaws
Scientists have designed a metal jaw that replicated what the T-rex could have done with its jaws. It was discovered that the jaws could have crushed through a car. Also, the Tyrannosaurids had an increasingly powerful bite as time went on (through changes in the skull) culminating in the T-rex with the most powerful bite. In fact, Jack Horner himself says “No meat-eating dinosaur had a more powerfully made head than t-rex…[scientists see] a lot of killing potential to it.” Why did the skull of the predatory tyrannosaurids continually evolve more and more powerful bites only to have the final tyrannosaurid (T-rex) sport the most powerful bite while simultaneously becoming a scavenger?

Argument from eyes
The eyes are in the front like a predator – and the skull was designed for good binocular vision – in fact, scientists think that the vision of tyrannosaurids progressed over time until T-rex had the best! Scavengers may need good eyes too, but the placement of the eyes implies predatory, rather than scavenger ability (a scavenger would benefit from a larger field of view rather than a focusing view like a predator’s binocular vision).

Argument by body design
There are two ways of classifying body design in animals – gracile (swift built) and robust (strong built). T-rex was built just as gracile as ornithomemus (an ostrich dinosaur). That is incredible! It means that if the quick, darting ostrich dinosaurs could grow to be 40 feet high but retained their proportions they would be similar to a T-rex! This also means T-rex was more gracile than humans – or bears. It’s not that scavengers can’t be gracile, but why does a titanic “scavenger” like t-rex need to be proportionally as swift as an ostrich dinosaur? As a predator, the necessity is obvious.

Argument by size
Towards the end of the Cretaceous herbivores evolved to be larger and larger. Consequently, their predators likewise became larger to be capable of hunting them. The T-rex itself actually evolved during its span to be larger and larger. Scavengers have no reason to increase in size in proportion to any other animals; their size is dependent upon other evolutionary factors, having no need of being in relation to the size of either herbivores or carnivores in its ecosystem. The T-rex is the last and largest tyrannosaurid. It makes sense that it evolved from earlier tyrannosaurids to be able to prey on the increasinly larger herbivores of the late Cretaceous. Remember, no one disputes that T-rex’s ancestors were predators. So, if it was a scavenger, why did it evolve to be larger than its predatory ancestors, and why did itself evolve to become larger over time if it wasn’t compensating for the larger herbivores?

Argument from neck
Its neck muscles were incredibly strong – not only stronger than all other theropods (all the bipedal, mostly carnivorous dinosaurs), but also stronger in proportion to its size than any other theropod. A carnivorous theropod has need of a strong neck in proportion to its jaws so they can work in tandem to rip huge chunks of flesh from prey (Horner himself says 500 lbs of flesh in one bite). A scavenger has no need for a supremely strong neck for ripping flesh; they eat rotting and soft meat.

Argument from nasal cavities
The T-rex had a specially designed skull with fused nasal arches which allowed it to be exceptionally strong so that it could apply huge pressure with its bites without harming itself. Scavengers, eating soft meat and not needing the force of their jaws to kill, have no need to protect themselves from the force of their own bite.

Argument from lungs
T-rex had a proportionately larger cavity for lungs than other theropods (carnivores). This ties in to the fact that it is a gracile (swift built) animal. It is designed for aerobic chases. As a scavenger is it just trying to be the first one to the carcass? Or is it because its prey runs away?

Argument of the conclusion inferred from all the other arguments
We have a slough of reasons that don’t merely indicate that T-rex was indeed a predator. They indicate that T-rex was probably the most powerful and effective predator of its size, or possibly even of any size of theropod (cetainly of any tyrannosaurid). In other words, it was not just a predator, it was a really good one. Had it been a scavenger not only would all of these reasons be evolutionarily vestigial, but there is no real indication it would have been a great scavenger - it would have been mediocore.

Countering the arguments for scavenger:

Rebutting the argument of size
The T-rexes are so large, some argue, that it needed so much energy to move and hunt it could not have possibly gotten enough through living prey. Therefore, it was not designed to hunt, but to scavenge. We don’t need science to disprove this one. Just a little logic. There were other carnivorous dinosaurs (though not many) that were larger than T-rex that nobody believes were exclusive scavengers. The giganotosaurus is a good example. Its teeth, neck, jaw muscles, and other predatory instruments were weaker and smaller than T-rex both absolutely and in proportion, yet no one believes it was exclusively a scavenger! If it, being larger than the T-rex but seemingly less capable (weaker jaw, etc.) could find enough energy by hunting to survive, why not the T-rex?

Rebutting the argument of sense of smell
Some argue that the large olfactory senses of T-rex made it a good scavenger. This is silly (or even disingenuous), because predators can benefit from a good sense of smell. In other words, sense of smell is not designed specifically for scavengers, it can be designed for predators as well. There are plenty of diverse examples today of creatures who use their sense of smell to hunt. (And scientists increasingly believe T-rex’s good sense of smell was designed for them to be good night hunters). Also as a bonus point of this rebuttal, the placement of the nostrils of T-rex suggests the sense of smell was not for dead, but for living meat. The nostrils are in the front like a predator’s, not back on the nose like a scavenger (scavengers eat soft, rotting meat which can clog up the nostrils, so scavengers evolve nostrils away from the end of the mouth).

Rebutting the argument of tiny arms
They had small arms, of no use for a predator. It is true scientists have not yet discovered the use of their small arms (though there are theories). However, a T-rex has plenty of obvious ways of hunting, killing and eating without needing its arms. And what purpose do they use if it’s a scavenger? And furthermore, there are other theropods (which are undisputed predators) with tiny forearms that are useless! If they can have small arms and be predators, why not T-rex? This is perhaps the silliest and easiest to explode argument for it being a strict scavenger.

Rebutting the argument of eyes
They had proportionally small eyes, and so some argue that maybe they couldn’t see well. This is silly. The proportion of eyes to head or body has nothing to do with the aptitude of the eyes. Blue whale eyes are smaller than a fist, which means in proportion to its body they are incredibly tiny. Yet blue whales do not suffer a lack of vision for it; animals simply don’t suffer bad eyesight because of the proportion of its eyes to its body. Bears, wolves and many other animals have small eyes to hunt with and do remarkably well. And T-rex has larger eyes than them! Besides, as stated above, the skull was designed for good binocular vision! This is almost as silly an argument as the tiny arms theory.

Rebutting the argument of speed
Because of their size and design, t-rexes could not run very fast, or possibly not at all. Predators need to be fast to catch prey, right? As stated before, the t-rex is actually more swiftly built in proportion than a bear or even a human, not to mention most other theropods. It was not bulky – in fact it was designed to be a quick walker, rather than a runner. Because of its size, a walking t-rex may have reached about 25 mph! The t-rex only has to be as fast or faster than its prey – it doesn’t have to be a runner or sprinter. The process of moving (walking instead of running) is irrelevant. How fast is your prey, and can you get it? In fact, in his own book Jack Horner says: “[t-rex has] massive legs to chase down prey.” Horner himself does not count speed as a primary reason he believes it was a scavenger.

Rebutting the argument of injury
Jack Horner also argues that if a t-rex ever fell, its own sheer weight would cripple it, and without effective arms it might be unable to right itself, therefore being forever pinned to the earth. The latter part of this point is disingenuous, because if a t-rex cannot move at all, how could it scavenge? So the real question is, should it be crippled, how could it hunt? The simple answer is, there are plenty of examples of animals today whose activities involve potential serious injury. I will take much of my response here from http://www.gavinrymill.com/dinosaurs/t-rex-hunter-of-scavenger.html
“A fall can be fatal to a giraffe and yet they frequently run. Monkeys die falling from trees but it doesnt mean they stop climbing…Injury in herbivorous dinosaurs is comparatively rare, however one quarter of all theropod dinosaur skeletons show a fracture in an arm or leg.”
Here are injuries sustained by an Allisaur:
• Fractured left lower leg bone
• Infected right foot bone
• Fractured tail
• Fractured abdominal ribs
• Fractured right rib
• Damaged claw sheath on the second finger of left hand
• Infected and fractured second and third fingers on the right hand
• The second finger of right hand twisted
• Fractured second finger on left hand
• Partial fracture in one right rib
• Infection in right shoulder
• Damage to left pelvic bone, a re-healed fracture.
Apparently, injury is just a part of life for a theropod. Why should t-rex be any different? This is not an evolved feature of the t-rex that allows it to scavenge. This is merely an inference supposing a hazardous life if it hunted.

Come on, after encountering many evolved features of why the t-rex was a great predator, we have yet to actually encounter an evolved feature that specifically denotes scavenging abilities! This is because there are none! There are only evolved features indicating it was a predator! This fact alone is a separate argument in favor of t-rex being a predator. The only evolved feature that is argued to specifically denote scavenging abilities is the sense of smell – but this could indicate that it was a good hunter as well, we could even posit it needed a good sense of smell for night hunting. Yet no single evolved feature that denotes it was a predator can reasonably be seen as a feature helping it to scavenge effectively!

My first argument was that Jack Horner is the only prominent paleontologist who believed t-rex was exclusively a scavenger and we, as non-scientists, should probably go with the super majority. Most of the arguments for t-rex being a scavenger were taken from his book or writings of people who have studied his work. However, in his book Horner reveals “I’m not convinced t-rex was only a scavenger, though I will say so sometimes just to be contrary and get my colleagues arguing.” So what have I been arguing for? Jack Horner is smart enough to know that there is too much evidence to pin t-rex down as exclusively a scavenger. And, as stated before, no one believes t-rex will pass up a free dead meal, so Horner isn’t completely wrong. But there’s just too much to say about how t-rex was an incredible killing machine. I believe she was the best that ever lived on land.
Arthur Petersen