Ferocious as she was, Sue, the Field Museum’s splendid 67-million-year-old Tyrannosaurus rex fossil, probably was a 7-ton plodder who literally shuffled through her world. But she may have done so in high style, tarted up with tufts of feathers.
Since Sue’s skeleton was found a decade ago, a wealth of new ideas have emerged about her species and an entire rogues’ gallery of huge killer dinosaurs, many uncovered more recently. This weekend, top scientists from around the country will discuss them at the Field.
A paleontologist who has been finding feathered dinosaurs in China will talk about the possibility that Sue also sported some feathers–perhaps for insulation at birth or as a display that would aid in communication.
Other scientists will propose that T. rexes simply were not born to run.
“Sue, I think, was not very fleet of foot,” said Matthew Carrano, a paleontologist at the State University of New York at Stony Brook.
He believes Sue grew to be about as large as any two-legged animal that ever lived–and ever will live. That size, he says, made her slow.
To mark the first anniversary of Sue’s unveiling, the museum is hosting an all-day symposium Saturday titled the Paleobiology and Phylogenetics of Large Theropods. A Greek word meaning “beast foot,” theropod is the name given to a suborder of dinosaurs that walked only on two feet.
Among them were Giganotosaurus, Carcharodontosaurus, Acrocanthosaurus, Suchomimus and Saurophaganax–dinosaurs roughly as big as T. rex at 40 or more feet long. All were equipped with powerful jaws and razor teeth, and had they ever met for a showdown, it’s not clear which one might have stood victorious.
“The fact is,” said Carrano, “if you could lay them down side by side, they’d be almost the same size, just a foot or two different in most cases.”
Such a showdown was impossible, as none lived in the same time or place.
Giganotosaurus, found in Argentina in 1994, lived 70 million years ago, for example; Suchomimus, whose bones were found in Africa by University of Chicago paleontologist Paul Sereno in 1997, lived more than 100 million years ago.
Different ancestors
Paleontologists had thought the giant theropods were close relatives along the chain of evolution, like modern-day African and Asian elephants. Scientists at the symposium will try to discredit that theory.
“I will lay down the idea that these are animals that evolved in their own places and times from different ancestors,” Carrano said.
The species grew or shrank to take advantage of niches in their environments, often changing body characteristics and life cycles as well, he said. Small theropods were shorter-lived, had more offspring and were swifter and more mobile hunters. Big ones lived longer, laid fewer eggs and were slower but extremely strong, able to take on and eat huge plant-eating dinosaurs.
“The very large theropods weren’t necessarily handicapped, like bears trying to chase gazelles for a living,” Carrano said. “They were more like bears chasing badgers. They weren’t all that fast, but they were fast enough to catch what they ate, things like duck-billed dinosaurs. T. rex wasn’t fast like a cheetah, but it didn’t need to be, either, in its world.”
Though springing from different ancestors and not closely related, the large theropods looked a lot alike, at least superficially, said Peter Mackovicky, a symposium speaker who will join the Field Museum as its resident dinosaur expert in July.
“They all had large heads, short forelimbs and powerful legs and tails,” he said.
Mackovicky said the large theropods probably developed some of the same body characteristics because those traits were crucial for each species to survive at the head of the food chain in its own time and place, hunting the same sorts of big prey.
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`Jurassic Park’
A lot of the new theropod theories have grown out of research by John Hutchison, another symposium panelist who has done biomechanical simulations at the University of California, Berkeley, of how theropods stood, walked and ran.
“I’ll look at the largest theropods in particular Saturday, using mathematical models to determine how much muscle mass they would need to move very quickly,” Hutchison said.
“The general pattern shows that, as animals get bigger and bigger, they need to dedicate a larger and larger proportion of body mass to supportive extensor muscle–muscle that keeps their legs from collapsing.”
Most of the large theropods weighed between 14,000 and 16,000 pounds. For such a large dinosaur to remain speedy, it would need such massive leg muscles that they would account for almost all of its weight, he said.
“My model shows it is dubious that a large theropod was a very fast animal,” he said.
Hutchison, who was a consultant to the animators who did the T. rex in the film “Jurassic Park,” said it probably was impossible for a large theropod to run–that is, to move so fast that at times both feet are airborne.
“The animation created for the movie never had the T. rex’s feet off the ground, though they used tricks of camera movement to make it look like everything was moving faster when it was chasing the SUV,” he said.
Hutchison studies the skeletal and muscular structures of living animals–including such presumed biological descendants of dinosaurs as alligators, ostriches and chickens–as a means of speculating on dinosaur locomotion.
Feathered fossils
Birds, feathers and how they relate to dinosaurs will be a large part of a public lecture at the museum Sunday by Philip J. Currie, curator of dinosaurs at the Royal Tyrrell Museum of Paleontology in Canada.
Some of the most startling dinosaur finds in the last decade have been feathered fossils that Currie has dug up in China. In his lecture, Currie said, he plans to explain how today’s birds evolved from small theropods.
“Even with animals like Sue,” said Currie, “you can learn about bird origins through them.”
Currie has recovered fossils of smaller theropod species in which perfect impressions of feathers are visible in the surrounding, fine-grained limestone. He contends that most smaller species of theropods probably were feathered, both for insulation and sexual display.
Large theropods such as T. rex may have been feathered for warmth as chicks, but they probably lost those feathers as they grew older, he said.
“We have small patches of fossil skin from the bodies of Tyrannosaurs in Alberta,” he said, “that show they didn’t have body feathers as adults.”
Still, Currie said the evidence doesn’t rule out feathers.
“It’s possible that, as adults, they retained some display feathers as crests on their heads or the end of the arms for display purposes,” he said. “We’ve known for a long time that they were very visual animals, relying on sight cues for mating or warning of aggression or whatever.”
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The Saturday symposium at the Field Museum is open to the public for a $15 fee. Fees for Currie’s 1:30 p.m. lecture and a subsequent round-table discussion at 3 p.m. are $12 each, or $18 for both.