Or not. One of the world's top paleontologists says T. rex was not a hunter at all. The fiercest giant of dinosaur lore was but a well-designed scavenger that had much more in common with buzzards and hyenas than with lions and tigers.
Tyrannosaurus, says Jack Horner, was a nasty-looking, hunched-over beast that was a lousy runner with mediocre vision and had spindly little arms that would have been useless in a fight. Even worse, if T. rex tripped and fell or was toppled by a stubborn foe, those arms could do little to dampen the impact of tons of falling dinosaur; the all-but-inevitable broken bones could easily prove fatal.
But T. rex would have been a masterful scavenger. Huge olfactory gear could have smelled a carcass from miles away, and legs designed for walking — not running — could cover vast distances in search of carrion, much as olfactory-gifted vultures soar over the landscape for hours. And those vicious teeth were adept not at slicing through choice cuts of meat but at crushing the bones and cartilage left behind by the true hunters.
Challenging a century of romantic perceptions — and widely held scientific conclusions — is hardly a popular chore. The killer T. rex, greatly beloved by children and filmmakers, is memorialized in models, movies, lesson plans and countless museum displays. Horner says the reaction to his hypothesis is often heated. His colleagues in paleontology seem largely unconvinced.
"People don't like it much," he says. "But we're doing science here. It's not an opinion poll. This is based on an accumulation of the evidence. It's just hard to change your mind when you grow up with the idea that this is a big, nasty predator."When Horner talks about Tyrannosaurus rex, it's hard not to pay attention. He's paleontology curator of the Museum of the Rockies in Bozeman, Mont., which accounts for 11 of the roughly two dozen T. rex specimens ever found. Teams that Horner led into the Hell Creek region of eastern Montana found eight of the giants in the past two years as part of an unprecedented effort in paleontology.
The five-year Hell Creek Project, the largest and most comprehensive ever undertaken anywhere, is reconstructing the paleoecosystem, with its dinosaurs, plants, mammals and mollusks, of the Hell Creek geological formation. This remarkable block of sediments — 300 feet (91 meters) from top to bottom and fairly bristling with fossils — spans the final chapter of the dinosaurs' tale from 68 million to 65 million years ago.
This remarkable formation lies open, like a window into the distant past, in the countless canyons and gullies that slice through the rugged and supremely isolated project area. The wind and precious rain continually expose new bits of ancient bone, potential jewels for the prospecting paleontologists, students and volunteers who hike the unending hills to collect clues to a world far different from ours.
Besides the astounding eight T. rex specimens, the project, now in its third year, has discovered an array of exotic creatures, including 50 horned Triceratops, plant-eaters that weighed 6 tons each; a half-dozen ostrich-like dinosaurs called Ornithomimids; a huge duckbill dinosaur, Edmontosaurus; an Ankylosaurus, a bulky herbivore with armored plates and a tail club; and a Torosaurus, a 4-ton beast with an enormous skull ringed by a bony frill.
The Hell Creek region has a long history as a haven of dinosaurs. Fabled dinosaur hunter Barnum Brown found the first Tyrannosaurus rex near the study area in 1902. Henry Osborn, Brown's boss at the American Museum of Natural History, named and described it — as a supreme predator. The T. rex of most of the past 100 years — Osborn's vicious killer — towered upright, its tail dragging the ground, its horrible mouth gaping open.
Morphological studies of the past few decades found a big problem with that: Standing upright would have broken T. rex's back. The giant must actually have stood bent over at the waist, its tail stretched out behind as a counterweight.
A key link in Horner's scavenger hypothesis came in 1990, when amateur fossil hunter Kathy Wankel brought him several curious pieces of dinosaur bone. They turned out be parts of a T. rex arm, the first ever found for the species. Horner excavated the "Wankel T. rex," which turned out to be 90 percent complete — with both arms.The arms turned out to be not just puny, but virtually useless. T. rex's upper arm, the humerus, is quite a bit longer than the forearm bones, the ulna and radius. This wasn't an arm designed for lifting things; in humans, both the upper and lower arm are roughly the same length.
The T. rex arm itself is very short in relation to the dinosaur's size, and much of that short length is buried in the animal's chest. What's left is a pair of spindly appendages that can't lift very much, can't reach the animal's mouth and can't even reach each other. These hands, Horner says, aren't good for much of anything but "scratching his belly."
The T. rex also reveals another feature that would create problems for a predatory creature: Its thighbone is longer than its shinbone. "If you look at any bipedal animal that runs fast, like an ostrich, you find a very short thighbone and a very long shinbone."
Consider the real predators of the Late Cretaceous, smaller and truly vicious bipedal dinosaurs such as Velociraptor, Deinonychus and Dromaeosaurus. Fossil skeletons (6 to 10 feet [2 to 3 meters] long) clearly depict agile creatures built for speed, with short, powerful thighs and long shins. Their arms were relatively long and strong, with vicious claws. One toe of each foot was armed with a long, sickle-like claw that could eviscerate its victims with a single swipe. Beneath large eyes was a mouth filled with sharp teeth serrated like steak knives. These were killing machines, and they probably hunted in packs like modern wolves.
Compare these consummate predators with Tyrannosaurus rex. "They are," Horner says, "just built completely different. When you add up all the features of a Velociraptor, you come to the conclusion that it had to be a predator. If you add up all the features of T. rex, it has to be a scavenger."
The trick, Horner says, is looking at this most popular of dinosaurs scientifically, to wipe away previous perceptions as though you had not been told since childhood that it was a terrifying killer. Then only the evidence can speak to you.
T. rex, he believes, came second to the kill, after the predators' sharp teeth had stripped away the prime flesh. An odious tyrannosaur — big, ugly and nasty — might then scare off the killers and hold them at bay long enough to use those enormous jaws and heavy teeth to chomp great chunks of bone, gristle and flesh from the huge carcass of, say, one of the very common Triceratops. Those are teeth that would have no trouble crushing big bones that the raptors could only gnaw.
Hints, if not proof, of that scenario come from a striking discovery of the Hell Creek Project. A sacrum (the bone at the bottom of the spine) from a Triceratops bears several deep, puncture marks. The holes are a good fit with T. rex teeth. It's very likely the bone represents scraps of a T. rex meal, although it offers precious little data about who killed the plant-eater. Nonetheless, the holes are on a part of the bone that would be inaccessible until the animal was torn apart.
Ugliness, Horner says, is a rather common trait of professional scavengers. Look at the stumpy, misshapen hyenas or amazingly homely vultures and condors. Ugly — along with a horrible odor gained from feeding on rotting flesh — likely is an adaptation that helps these creatures drive even vicious predators from a corpse. And T. rex was no beauty.
The "tyrant lizard king" seems to have had something else in common with vultures: an extraordinarily keen sense of smell. Vultures, it is said, can smell a corpse up to 25 miles away. Horner made a brain cast from within a T. rex skull and found the optic lobe and nerve were very small, suggesting mediocre eyesight. But the olfactory lobe that handles smell was enormous. Using a medical CT scan, he compared the olfactory passages of a vulture and a T. rex, an analysis that revealed striking similarities. T. rex was an outstanding smeller.
While vultures can coast on thermal air current high above the land, T. rex was earthbound. A scavenging giant would need to scout the landscape looking for the scent of a kill, then cover miles before it could hope to scatter the feasting predators and claim a meal. That's a job for long-distance walking, not running, and that's where the long thighbones are useful.
An intriguing piece of research involves two Daspletosaurus skeletons, one an adult and the other a juvenile, found recently in western Montana. Daspletosaurus, very similar to T. rex but slightly smaller and about 7 million years earlier, is probably a direct ancestor of the "tyrant lizard."
Horner plans much more comparative study with the fossils, but one initial observation jumps out: The thigh and shin of Daspletosaurus are about the same length, while T. rex's thigh is significantly longer than its shin (a disparity that favors walking over running). Horner suggests that change could mean T. rex was evolving into a better-adapted scavenger than its ancestor.
Horner also hints at another trait that T. rex might share with vultures, although he stops just short of stating it outright. Asked if the sheer abundance of T. rex fossils at Hell Creek suggests anything interesting about the species, he notes that a flock of about 30 turkey vultures roost near the project's main campsite. Every morning, the flock flies off over the hills, and every night it returns to roost together. Yet, "we only see one eagle [all by itself] every once in awhile."
And, he adds, the vultures usually coast through the skies alone, but "whenever you have anything dead out there, you see dozens of them [circling overhead or surrounding the carcass]. I throw that out just as comparative biology. It's an interesting thing to think about."
Another interesting, if unclear, fact is that the list of dinosaurs collected at Hell Creek does not include any serious predators, if we accept T. rex as a scavenger. Yet a large herbivore, Triceratops, was prevalent, with roughly 50 individuals found. Horner agrees that something almost certainly had to be hunting so prevalent a prey animal, "but we haven't found it yet. We have found a lot of teeth of Dromaeosaurus," a good-sized predator that likely hunted in packs and could have killed the three-horned dinosaur.
The most common professional objection to Horner's scavenger hypothesis is that most predators will scavenge if they stumble across a free meal, and many scavengers will kill prey when the opportunity presents itself. T. rex, this argument goes, was almost certainly an opportunist — both a scavenger and a predator as the situation dictated.Horner gives no quarter on this issue. "It is," he says, "bad science. What's the evidence for hunting? Just opinion?" Is there any evidence at all that Tyrannosaurus rex ever hunted? "None whatsoever."
As fascinating and controversial as the T. rex hypothesis is, however, the Hell Creek Project is after much bigger scientific game: a comprehensive snapshot of an ecosystem that disappeared 65 million years ago. By the time the five-year project ends in two more years, Horner says, "we should have the data to reconstruct this ecosystem."
No paleontologist has ever attempted such a large system reconstruction. Until fairly recently, Horner says, dinosaur research had a great deal in common with butterfly collecting — basically digging up bones and putting them on display with too little thought given to the context in which the giants lived.
Hell Creek is an ideal place to start. The formation is relatively continuous, clearly bounded and easy to identify. The sediments span about 3 million years, roughly the estimated duration of a species — before it disappears or evolves into a new species. That should permit an evolutionary study of how dinosaur — and perhaps mammal, mollusk and plant — species changed over time and in response to their environment.
And the 3 million years of Hell Creek end at a critical moment — the KT Boundary that marks the extinction of the dinosaurs some 65 million years ago.
The multidisciplinary project is a cooperative effort of the Museum of the Rockies and the University of California at Berkeley's Museum of Paleontology in cooperation with the U.S. Fish and Wildlife Service. Thirteen senior scientists are exploring the ancient ecosystem, along with other professionals, graduate students, some undergraduates and volunteers. These varied experts are cataloging and analyzing this one piece of prehistory from many directions and all of its most important components.
Beyond a few general numbers and the T. rex fossils, Horner isn't nearly ready to discuss what the project is discovering. Much more data must still be collected.
The ambitious program is almost entirely supported by individual donors and foundations. The main underwriter is Nathan Myhrvold, retired chief technology officer of Microsoft and one of the project's senior scientists. Other supporters include Mary and Terry Kohler, Catherine B. Reynolds and James Kimsey.
Other contributors are Universal Studios, for whom Horner consulted on the three Jurassic Park movies, and Discovery Channel, which is broadcasting Valley of the T. Rex — a documentary on Horner's work with dinosaur animation.
Myhrvold says his support grew from a longstanding fascination with dinosaurs and the ambitious goals of this field project, as well as the meager funding available for such research. "If you're doing something [providing financial support] that is just like everybody else, the net impact is smaller," he says.
"Dinosaurs get a fantastic amount of interest from the public, but the budget of just the last Jurassic Park film is probably greater than what has been spent on dinosaur research in all of history. It's kind of odd that this is the case."
Robert Locke is the executive editor of Dinosaur Magazine. This article has been reprinted with the permission of Dinosaur Magazine.