Paleontologists at Brigham Young University have discovered that portions of a huge dinosaur pelvic bone complex are hollow.

The bone mass was discovered last summer by BYU researchers working at Dry Mesa Quarry near Delta, Colo.The fossil, measuring 73 inches long by 52 inches wide, consists of the sacrum, several fused vertebrae situated immediately behind the tail, and the ilium, the upper bone mass of the pelvic girdle, known in laymen's terms as the hip bone.

Wade E. Miller, a paleontologist and chairman of BYU's Department of Geology, said he was surprised to learn that the ilium of the dinosaur's pelvic girdle is hollow.

"To my knowledge, and to the knowledge of other paleontologists I've talked with, this is the first time a bone from the sauropod group of dinosaurs has been found to be hollow," Miller says.

Ken Stadtman, a paleontologist and assistant curator of the BYU Earth Sciences Museum where the huge dinosaur bone is being prepared and studied, said in all his years of working on sauropod dinosaur bones, he has never seen a hollow one.

Scientists believe the bones belong to a "Supersaurus" dinosaur, a massive plant-eating creature that lived between 130 million and 180 million years ago during the Jurassic and Cretaceous Periods.

Miller believes the "Supersaurus" is a member of the Diplodocid family. These dinosaurs were much longer, more slender and more lightweight than the brachiosaurids (such as the five-stories-tall, 100-ton "Ultrasaurus") but nonetheless were incredibly huge creatures.

The particular bones being studied suggest a youthful beast that lived about 135 million years ago. It probably measured close to 120 feet in length and weighed at least 30 tons, Miller says.

Interestingly, the bone walls of the ilium are fairly thin, ranging from eight millimeters thick and narrowing down to about two millimeters thick in places. In between the walls, the bone cavity is filled with sediment.

Visible within the bone walls are slender struts of bone that Miller says probably kept the large bone mass from collapsing in on itself - another indication that the bones were at one time hollow.

There is no sign of leaching on the exterior of the bones. They are smooth with no tell-tale etching marks that would suggest leaching had taken place.

Miller speculates that the hollow bones held a soft tissue such as bone marrow and were the site of blood-cell formation.

"The hollow bones would also mean that the dinosaur's body was more energy efficient than previously believed and that bone was placed only where it was really needed," he says. "This dinosaur in particular may have been more lightweight and energy efficient than we thought."

When fully prepared, the pelvic bone mass will likely weigh one-and-a-half tons.

Over the years, BYU researchers have discovered other bones from the "Supersaurus" dinosaur, including a couple of neck vertebrae, several tail vertebrae, and two shoulder bones or scapulae.