Dinosaurs in Motion, Carl Zimmer

-Editor’s note: Though this article is from 1997, I think it still is relevant as to what makes Kent Stevens tick., and besides, the work he does is just so interesting.

. . . . While Myhrvold* has been engrossed in the tail end of sauropods, University of Oregon computer scientist Kent A. Stevens has been busy at their front end, trying to figure out how they ate. . . .

Stevens is another scientist for whom computers are stock-in-trade; he studies how we see in three dimensions--that is, how we perceive depth from textures and contours--and his basic research often involves experiments that use 3-D computer graphics. The information he collects helps him in his other lines of research, such as enabling robots to see and making virtual reality systems feel less virtual and more real.

While watching Jurassic Park in 1993, Stevens was surprised by the forward-facing eyes that had been given to Tyrannosaurus rex. As an expert on depth perception, he knew that if the depiction was accurate, the dinosaurs might have had stereovision like our own. “That started me on some formal research on vision in many species of dinosaurs,” he says. In particular, he looked at the variety of binocular vision among predatory dinosaurs: some, he found, had a wide overlap in their two fields of vision, like a cat. With their wide binocular field, these dinosaurs would have been good at navigating three-dimensional space--they could have been catlike stalkers. Other dinosaurs had a narrow overlap of visual fields and would have relied on their stereovision only when the prey was close. They would have been more like crocodiles, lying in wait for their prey and then lunging or sprinting forward for the kill.

Soon afterward Stevens wanted to show one of his computer science classes how to build a piece of software from scratch. With dinosaurs now on his mind, he constructed software that could model dinosaur skeletons. At about the same time, he became friends with Michael Parrish, a paleontologist at the University of Northern Illinois. . . . Stevens and Parrish wanted to see what kind of movements sauropods could make with their necks. . . .

“It's very difficult to eyeball these things and say, ‘Okay, this shape will give me this much flexibility,'” says Stevens. “You really have to put it in the machine.” He and Parrish have visited museums around the United States and Europe over the past two years, recording the dimensions of sauropod vertebrae. Hovering in cherry pickers or crawling around dusty basement collections, they have made dozens of measurements of each bone, sometimes making rubbings of the zygapophyses as if they were gravestones. Back in Oregon, Stevens feeds the numbers into his computer and has it build the dinosaurs.

The program lets Stevens find the natural position for each sauropod's neck by calculating the stance in which its zygapophyses fit snugly against each other. From there he can explore the range of movement they were capable of by pulling their necks until the zygapophyses either press against each other or slide too far apart. . . .

Stevens has found that the neutral poses of their necks are about the same--not gently sloping upward as you'll see in museums or textbooks, but tilted downward. Apatosaurus would normally have held its head just a few feet off the ground; Diplodocus’s head would have hung down like the head of a hammer, hovering just inches above the ground. In their necks’ mobility, however, the two animals are quite distinct. Apatosaurus could lift its head 17 feet into the air and move it 13 feet to the right or left. It could bend its 16-foot neck in a U shape so that it could look directly behind itself. It could even twist its neck into a forward-facing S. Diplodocus, though it had a longer, 20-foot neck, was far stiffer. It could lift its head only 12 feet above the ground and could bend only 7 feet or so to either side.

The other sauropods that Stevens and Parrish have studied show a similar split between the contortionists and the straitjackets. . . .

The stocky, 59-foot-long Camarasaurus may have been able to hold its neck almost vertically--which, according to Stevens, is actually a rare pose for sauropods. If you have an image of sauropods holding their towering necks high like giraffes, you're probably thinking of the much- painted 80-foot-long Brachiosaurus from the American West. Yet Stevens has shown that such a pose is beyond its ability. . . . “What you end up with in Brachiosaurus,” says Stevens, “is a neck that is straight out and high but that can't flex much. . . .”

One of the oddest results to come out of Steven’s computer is the extent to which some sauropods could reach down. The lowest that Brachiosaurus--the airplane-stairway dinosaur--could get its head was about five feet off the ground. It might have faced the same troubles trying to drink water that giraffes face today, but whether it splayed its legs apart like a giraffe is anybody’s guess. Apatosaurus and Diplodocus had no such difficulties: when Stevens brings their necks down as far as the zygapophyses will allow, their heads end up as far as six feet underground.

Stevens and Parrish have been scratching their heads over this finding.

(Editor’s note: Maybe Friday evening he’ll tell us if anything further has been interpolated regarding the feeding habits of sauropods.)

*(At first I tried to recollect my Beowulf.) >From Wikipedia online: Nathan Myhrvold, formerly Chief Technology Officer at Microsoft, is cofounder of Intellectual Ventures, which is seeking to build a large invention portfolio. . . . He is a prize-winning nature and wildlife photographer. He is also involved with paleontological research on expeditions with the Museum of the Rockies. His work has appeared in scientific journals . . . . He has contributed $1 million to the SETI Foundation for the development of the Allen Telescope Array, planned to be the world's most powerful telescope.