Michael Parrish, a researcher at Northern Illinois University, said that he and a colleague used a computer model of the neck fossil bones of two types of dinosaurs, Diplodocus and Apatosaurus, to discover how well the huge animals were able to move. Apatosaurus was once called Brontosaurus and is one of the best known of all dinosaurs.
What they found in their study, said Parrish, was that the even though dinosaurs had necks that could be 40 feet or longer, the animals could not raise their heads much more than 10 feet. For the most part, he said, they held their heads straight out or down, not up.
"The maximum amount they were able to raise their heads was just a little bit above the height of their back," said Parrish. "If you raise the neck any higher, the vertebrae run into each other and the back locks up."
This contradicts the popular view that the long-necked dinosaurs routinely cropped leaves from the top of trees and were able to stand on their hind legs and reach the highest limbs. "It was a surprising result," said Parrish. "We didn't think there would be any problem with them raising their heads, but it turns out there is a real, physical limit."
Parrish added, "I don't think our study answers whether they could rise up on their hind legs, but if they did there would be a blood pressure problem. I don't think they would use that as a predominant way of feeding, as some people have suggested."
The two animals studied are in a group known as Sauropods. These were massive animals with long tails and long necks and small heads. The Apatosaurus, for instance, is thought to have weighed up to 100 tons, stood up to 70 feet in height and had a head-to-tail length of about 130 feet.
Sauropods lived from 200 million to 65 million years ago and were one of the most successful animals that ever existed. Their fossils are the most common in nearly every one of the ancient ecosystems, said Parrish.
For years, scientists have depicted the animals as browsing from high vegetation or swimming in pools with their long necks sticking up like living periscopes. Most museums with Sauropod fossils display the animal with the head held high. But Parrish said there long have been doubts that the animals' hearts were strong enough to pump blood up the long necks to the head. Some researchers even suggested double hearts as a solution to this problem.
The new study, though, shows that neck bones kept the Sauropods from raising their heads. The bones favor a position where the head was low, swinging from side to side for grazing, and they were always grazing. "These animals were so big they had to eat almost constantly to get enough energy," saiParrish.
J. Keith Rigby Jr. of the University of Notre Dame said he was happy to see some researcher was, at last, "taking a serious look at what has been accepted as dogma in the past. I am not surprised at his findings." He and other researchers have long suspected that some of the assumptions about how well the Sauropods could move their heads "violated a whole group of biophysical laws."
The study appears in latest edition of the journal Science.