Killing a Legend (cont'd)

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.