Your path: A Look at T-rex
My What Big Teeth You Have
A Look at T-rex
by Elena Victory, Ph.D.
Department of Science and Mathematics
Was America's favorite monster a scavenger or a predator and does it really matter? To a certain group of scientists and dinophiles, the answer is a resounding YES!
A great deal of time and money has been allocated to determining whether T. rex aggressively hunted or was a connoisseur of carcasses. One image conjures up strength and glory, while the other seems rather mundane or even repulsive.
The name Tyrannosaurus rex or "tyrant lizard king" illustrates what its discoverer must have thought from the start. Armed with a massive skull containing 7-inch steak knife teeth, the Mesozoic king of beasts must have been a predator—or was it?
Things went awry for the king's reputation in 1917 when Canadian paleontologist Lawrence Lambe found a very close cousin, Albertosaurus. The Canadian rex had very little tooth wear and Lambe was quick to conclude this meant the beast didn't use its teeth as a predator. Lambe neglected the fact that tooth replacement in theropods was rapid and he essentially reported this animal was nothing more than a huge garbage disposal.
In recent times, Jack Horner (paleontologist at the Museum of the Rockies) and a few others have also supported the view of T. rex as scavenger.
Horner first notes the useless arms. Hard to believe, but an adult man could have won an arm wrestling match with a rex. The massive legs and a 12,000-pound body 12 feet off the ground meant that T. rex could only achieve a fast lumber.
Second, Horner viewed the braincase and eye sockets as small, even though the skull was massive. A pea brain or beady eyes are not the hallmark of a great predator.
He does note that the olfactory lobes (the site of smell) inside the brain were huge. With olfactory lobes proportionately similar to modern vultures, this meant T. rex probably could smell rotting flesh from miles away.
If it couldn't see, couldn't run and couldn't grasp, then ambush tactics weren't necessary. All T. rex had to do was to follow the herds of migrating herbivores, culling out the sick, the young or wounded (much like modern hyenas follow zebras of the Serengeti). Its size alone would have scared away the competition.
As consulting paleontologist for Jurassic Park, Horner told directors T. rex could never chase down a jeep of scientists. At best, it might have bitten a broken-legged Dr. Malcolm, and then returned for him a few days later once he stunk. Directors did not follow this lead but did opt for the poor vision theory.
After the Chicago Field Museum purchased "Sue" (an 8.36 million dollar T. rex with a scandalous legal history), a long-awaited CAT scan was performed on her skull. The results were even more revealing. Indeed the olfactory lobes were huge. After their volume was subtracted, the actual brain mass was still human-sized, bigger than any other existing dinosaur. While this does not imply more intelligence, it does not support T. rex as a pea brain either.
The rest of the brain was largely cerebellum. This is used in birds and mammals for instinct (attack, defense and territoriality), sensory integration, precise movement, agility, equilibrium and learned intelligence.
The hole for the optic nerve was also huge—more like an optic cable—allowing room for a softball size eyeball. Since crocs and birds see in color, it is presumed dinosaurs could too. The eyes sockets faced forward, providing overlapping fields of vision (stereoscopic or binocular). This would allow T. rex to gauge distance and perceive depth.
Researchers can't speculate too much about hearing—except to say T. rex could probably hear just fine. Birds hear well in high frequencies (consider their songs) and crocs hear well in low frequencies, so T. rex could probably hear low to medium tones (like heavy footfalls).
All in all, this was an animal with the bells and whistles of a predator. Evolution selected away from arms and reconfigured a killer skull. Certainly, Dr. Grant and the boy would be dead meat on that dark rainy night standing motionless in front of the jeep—for this predator could probably judge color, shape, motion, distance and hear and smell just fine.
Skull features aside, other scientists look at the argument through the larger lens of evolutionary biology.
It is ecologically unfeasible for any animal to operate purely as scavenger. Modern vultures and condors are as close to a pure scavenger as it gets. They expend a great deal of calories soaring great distances for the next occasional carcass. Even then, vultures have been filmed attacking newly hatched sea turtles. Jackals and hyenas scavenge somewhere between 20-50 percent of their diet depending on the season.
In all likelihood, T. rex could not have been lying around all day conserving energy. Since it couldn't fly to cover distance, it probably had to employ both predatory and scavenging strategies.
Bob Bakker suggests that if limb bones were compared (calf length compared to thigh) and further compare T. rex's longer limbs to the shorter limbs of potential prey, then rex only needed to be slightly faster then what it was eating.
Long limbs are the mark of a runner. When the evidence of skull and limb features are combined, the longer limbs and depth perception meant a T. rex could bolt, lunge or feint—important for a predator's bag of tricks. Forearms had to go in order to compensate for the more compact torso and heavily muscled head and neck.
T. rex, like most of today's mammals, birds, crocs and lizards, capture prey with their mouths, not forelimbs.
"I'm not convinced T. rex was only a scavenger, though I say so sometimes just to be contrary and get my colleagues going," writes Jack Horner today. "To my mind, T. rex was simply the greatest opportunist of them all."
So it's settled then—my favorite monster redeemed itself—in the form of the most powerful land predator the world's ecosystems ever saw.
I feel a whole lot better.
