

Posted Jun 11, 2012 by Paul Wallis
Predator X s jawbones
The jaws of "Predator X" compared to the jaws of a T. Rex
From History Channel
You can’t be a paleo fan without getting constant surprises, and this idea was fascinating. I didn’t know the half of it.
Dr. Phil Currie, a Canadian palaeontologist, is the proponent of the T. Rex pack hunting idea. You need to be a particular type of person to be a palaeontologist. You need patience, an eye for detail, and if you’re a professional, you need to be prepared to wait a decade or so for recognition of groundbreaking work. What I didn’t know was that Dr. Currie also had to wait a long time for his theory to get some breathing space.
In 1999, Discover Magazine published the original basis of Dr. Currie’s theory. In 2011, Dr. Currie’s theory became a Discovery Channel show. In 2012, he began to get some in my opinion long-overdue awards from Canadian academic and provincial sources.
Killer packs of T. Rex- A big bite out of some old ideas
Dr. Currie’s work is significant for one particular element- Depth of perspective. The chronic problem with most dino studies is a “mechanical” approach. The idea that dinosaurs were “reptiles” was axiomatic for over a century until it was found they were much more closely related to birds, and couldn’t have been purely “reptilian”, either biologically or in behaviours.
(The “reptile” argument also dies an ignominious (if unduly slow) death when you consider that no reptile ever had the shapes of the big dinosaurs, particularly T. Rex and its relatives. If the shape is different, the behaviour has to be different.)
Currie’s work hits at one of the lingering myths about T. Rex- That they were big dumb eating machines, and could only scavenge for food. In fact, his theory demolishes that theory, pretty much entirely. Currie discovered that the T. Rex brain, previously derided for its size, had enormous sensory capabilities. You don’t need to be super-sensory to be a scavenger. You need smell, but that’s about it. Even the archetypal mammal scavengers aren’t actually scavengers per se. Hyenas, for example, are active hunters, with good senses.
T. Rex had a huge arsenal of visual, olfactory and hearing capabilities. T. Rex even had a huge inner ear, able to pick up infrasound. Infrasound is low frequency sound, inaudible to humans, but it travels for a very long way. You don’t need infrasound to hear a corpse of some animal rotting. You need it to detect movement from live prey.
The killer packs, however, are a further revelation. There are some subsidiary arguments which back up this theory in several ways. T. Rex could not possibly have been unaware of other T. Rex in their hunting range. Even crocodiles will tolerate the presence of other crocs (most of the time), and their mass presence also means good chances of participating in a kill. Crocs don’t have the mental equipment of T. Rex, as we’ll see below.
The brain, interestingly, sets T. Rex apart from reptiles and even other dinosaurs. According to Currie, T. Rex was about six times smarter. You can see some interesting parallels in reptile and dino brains, but when you equate them, you can see how well organised T. Rex really was, mentally.
A crocodile brain does have a morphology which is similar to some very basic dino types. If you check out an Allosaurus brain, it’s also similar, but hardly the same. Now see the current version of a T. Rex brain. It’s a very different brain, for a very different animal. T.Rex brains are packed with sources of sensory information, including very good eyesight.
(I was looking for an image of Currie’s T. Rex brain, but couldn’t find one online. The Discovery Channel show is probably the best bet for seeing the huge differences and incredible sensory capabiltiies of these gigantic beasts.)
Brain size, by the way, particularly for a highly evolved animal, is not necessarily an indicator of anything. Some ants have tiny brains, but can function very efficiently in the incredibly complex world of chemical signals in an ant colony. The probability is that evolution streamlines brains and makes them more efficient, particularly for core functions.
The most recent identified case of human brain evolution was a 20% increase in size circa 1000AD, probably the catch up from a massive shift in behaviours and requirements for logic. That doesn’t mean the human brain has stopped evolving, it means it adapted to its environment. The dino brain of T. Rex looks like a very highly developed bit of machinery, able to use its huge sensory capabilities very efficiently. T. Rex had longer to develop its brain than the whole of human and prehuman history. I think we can cut them some slack on having the right brains for the job.
After all, T. Rex doesn’t have to go and write a report after a kill or go dancing or catch a plane back to New York. Its brain was there to do a job, and it obviously did just that. Functionality and brain size send very mixed and often misleading messages, and the one undeniable fact about T. Rex is that it was an extremely successful animal. Success is a result of efficiency in nature.
T. Rex packs- A winning hand, every time
Not to oversimplify- The T.Rex environment, if comprised of a lot of major and minor predators, and quite possibly a different predator/prey ratio, means that if you’re a predator, you need a good working methodology to get your food and survive getting it. It’s well known that an individual T. Rex, confronted with a lot of hard targets like Triceratops, Ankylosaurus and fast moving smaller dinosaurs, would have a hard time getting food reliably. The heavily armed and armoured dinosaurs, in fact make a good case for evolved prey animals with serious arguments against their predators. These animals were highly successful, even in a T. Rex dominated environment.
That equation changes dramatically in favour of the predators, however, if you have a pack of T. Rex. Few other predators would be dumb enough to try to argue with a T. Rex pack. Even a herd of Triceratops would have had great difficulty preventing a successful kill by a pack. The odds are in favour of at least one kill, probably more.
T. Rex, like a shark, was capable of delivering one single bite which would kill its prey either directly or by blood loss and shock. Survival would be more likely to be luck than good management on the part of the victim. This is a very economical method of hunting, reducing risk in contact with prey and delivering massive damage with the famous “super bite” of about 4 tons, compared to about 1 ton for a crocodile. T. Rex could actually bite through bone, and digest it. There are so few herbivore bones in some T. Rex hunting areas that it is now a big question about exactly where these bones are, because there should be literally millions of them.
Currie’s theory goes further than lots of big T. Rex hunting their prey, however. He suggests generational teamwork, and that the much faster young T. Rex, able to run down prey, would have been followed by the bigger adults, after which it was game over for the prey.
This makes sense in one particular way- The young T. Rex also had severe bites for their size. They were credible predators in their own right. If the prey survived their attack, they’d be in poor shape to handle the adults. A big Triceratops would be a very tough proposition for juvenile T. Rex, but they were very agile, and could have delivered serious wounds relatively safe from the dangerous but comparatively slow gore of the Triceratops. They could also run down the fast moving two legged herbivores, which were too fast for the adult T. Rex except in an ambush scenario.
In effect, a T. Rex pack is a battle group. You have fast scouts and attack units, followed by overwhelming force. In military terms, that’s best practice, even today. The T. Rex pack wouldn’t have any threats, except possibly other packs, and those would be well enough aware of each other to avoid confrontation thanks to good sensory equipment. That’s another bit of survival insurance which may well have gone missing in the debate about dino packs.
One of the joys of amateur palaeontology is that you get to do your own thinking. The whole discipline, in fact, is about thinking. Readers will enjoy following up on Curries theory and making up their own minds. Just one consideration- Remember we’re turning up more every day in palaeontology than we did in the first 100 years since the first dino fossils were discovered. Whole slabs of dino ecology are being found which are changing the picture by the second. The only way to see theories is with an open mind. I hope Currie’s guts in reinforcing this axiom of the science are also recognized.