The long-necked dinosaur Diplodocus and its close cousin Apatosaurus did not nibble treetops as commonly assumed but munched most of their food near the ground. Computer modeling of these dinosaurs' bones, reported in today's issue of Science, suggests that the swanlike neck posture commonly envisioned for these animals would have been impossible.
When paleontologists first assembled the fossilized bones of the 21-meter-long Apatosaurus roughly 100 years ago, they posed its neck parallel to the ground. But in recent decades, the theory that dinosaurs were warm-blooded and energetic has led researchers to propose more radical postures for many species, including the more dramatic swan-necked pose.
The heads-up assumption raises problems, however, such as the difficulty of pumping blood to a brain that is more than 10 meters above the body. So J. Michael Parrish of Northern Illinois University in DeKalb and Kent Stevens of the University of Oregon, Eugene, decided to make a rigorous investigation. First, they visited the Carnegie Museum in Pittsburgh, where skeletons of Diplodocus and Apatosaurus are mounted side by side. "We had to climb up on the cherry pickers and ended up taking about 33 measurements for each vertebra," Parrish recalls.
They then created model skeletons on a computer and maneuvered the necks as far as they could go while preventing adjacent vertebrae from touching. Also not allowed was overstretching of the joint cushions that would have existed between vertebrae, which they modeled on those of bird and crocodile necks. They found that although Apatosaurus could have reared its head upward somewhat, Diplodocus could barely have raised its head above the level of its back. Neither could have assumed the dramatic S-shaped curves often depicted. A relaxed neck position, the researchers found, would put the head roughly 1 to 1.5 meters above the ground.
The reconstructions suggests these dinosaurs mainly fed on ferns and other low vegetation, Parrish says. That makes sense given that the low-growing leaves were probably more nutritious than pine needles and other treetop vegetation of that era, he says.
The study brings relevant new data to the question of dinosaur posture, says paleontologist Jeff Wilson of the University of Chicago. This and future neck studies, he says, could be combined with other evidence for feeding habits to present an overall ecological picture of sauropods. "It would be interesting to look at other animals and see if certain necks go together with certain feeding strategies," he says.