Huge dinosaur bones discovered hollow.

Huge dinosaur bones discovered hollow

Paleontologists studying the gigantic dinosaur "Supersaurus" report the animal had an inner cavity within portions of its pelvic bones -- a finding that puzzles those trying to understand Supersaurus and other large dinosaurs.

When researchers from Brigham Young University in Provo, Utah, unearthed these pelvic bones in Colorado last summer, the sheer size of the pieces amazed scientists. Measuring more than 6 feet long, the fossilized bones include the ilium, or hip bones, and the sacrum -- several vertebrae fused together and attached to the ilium for strength (SN: 9/24/88, p. 203). The bones indicate the animal was up to 120 feet long and not fully grown, says Brigham Young paleontologist Wade E. Miller. These measurements make Supersaurus one of the longest dinosaurs known.

While removing the fossilized pelvic bones from their rocky bed of some 135 million years, the Utah researchers were able to examine portions of the fractured ilium in cross section. Instead of finding solid fossilized bone in the front section of the ilium, they discovered the cross section looked something like a sandwich, with walls of bone on either side of silt/clay rock, the scientists announced last week.

During the dinosaur's life, Miller explains, some soft material filled the ilium. But this inner matter would have decayed after death, leaving a void later filled by fine particles of silt and clay that entered the bone through fractures. Parts of the sacrum also show hollow features.

Scientists who study the largest dinosaurs -- a group called sauropods, which includes Supersaurus and Apatosaurus (better known as Brontosaurus)--do not know what to make of the bones. While some small carnivorous dinosaurs had hollow bones, "it has never been mentioned in the literature [on sauropods]," says sauropod authority John S. McIntosh of Wesleyan University in Middletown, Conn.

Yet hollow ilia might not be that unusual among sauropods. McIntosh says researchers may not have recognized such features while examining fossils before. Moreover, paleontologists have not had the opportunity to check the insides of unbroken dinosaur bones. McIntosh says computerized axial tomography, also known as CAT scanning, or other nondestructive tests might reveal whether intact fossils are solid bone.

Aside from finding fine-grained rock inside the bone, Miller says, other signs indicate parts of the Supersaurus pelvic bones were hollow. Much of the recently excavated ilium is crushed, possibly from the weight of sediments accumulating on top of the bone as it fossilized. The Utah researchers have also found bony struts that span the inside of the ilium, probably strengthening the pelvis, which helped support an animal weighing as much as 30 tons.

Miller and others have speculated that hollow bone sections served to cut down on body weight and reduce the amount of bone the animal had to produce. "What I suspect, and this is speculation, is that there was probably something like marrow in there. It may have been a site for blood cell formation," Miller says.

McIntosh questions whether weight considerations could explain the hollow cavity. "If this thing were hollow, something had to be inside. And if liquid were inside, I'm not sure it would really cut down on weight that much."

The perplexing pelvis is not the only topic of debate among scientists studying this creature. Supersaurus is an unofficial name given to a group of oversized bones from the Diplodocidae family found near each other. Some researchers believe all these bones belonged to one type of dinosaur, yet others say the bones may represent several types of large diplodocid dinosaurs. Scientists are also trying to decide whether Supersaurus belonged to the same genus as the similar, but smaller, Diplodocus.