It was just another routine day of fossil hunting in Arizona's stark but spectacular Petrified Forest National Park. Suddenly, at the foot of a salmon-colored sandstone cliff, Brian Small stumbled on a chalky white ankle bone the size of a dog's hind leg. From its odd shape, the student knew it was something special.
But only last week did scientists at the University of California at Berkeley reveal how rare the find was: Probably the oldest dinosaur fragment ever found in the Northern Hemisphere and perhaps the world -- part of a spectacular series of bones researchers believe will yield new information about how the reptiles lived 225 million years ago.
``It was an extremely fortuitous find,'' says Michael Greenwald, a scientist at Berkeley's Museum of Paleontology and member of the team that found the remains.
The bones are believed to be 10 million years older than any major fragments previously found in North America and Europe. Dinosaur specimens found in the 1950s and 1960s in South America were thought to be about 225 millions years old. But more recent dating indicates they may be younger than that.
The remains include part of the skeleton of one dinosaur and fragments of at least one, and perhaps several, others. It's uncertain exactly what type of creature the bones came from. Scientists speculate the skeleton may represent a new family of plant-eating dinosaurs that were related to the plateosaur, an ancestor of the lumbering, goose-necked brontosaurus.
Judging from the bones, the creature was believed to be about the size of a small ostrich, walked on four legs, and weighed about 200 pounds. The animal was probably seven feet long and stood less than three feet tall at the hip.
The bones were found in the forest's Painted Desert in northern Arizona. Mr. Small, a graduate student from Texas Tech University who was a member of a Berkeley team, came upon the fossils last August near the base of a 500-foot cliff -- a site scientists have dubbed ``dinosaur hollow.''
What is unusual about the find is the completeness of the well-preserved bones. Many dinosaur fragments have been found in the Petrified Forest. But this is the first time such an extensive part of a skeleton of this age has been found at a single site.
``The real value is that it seems to be a fairly complete discovery,'' says Dr. Edwin Colbert, a curator at the Museum of Northern Arizona in Flagstaff and a leading authority on dinosaurs. Among the fossils was a complete hind leg with toes and claws, ankle bones, several thigh bones, ribs, vertebrae, and other fragments that have not yet been classified.
Some of the bones have already been shipped to Berkeley for analysis. But the leg bone, entombed in a sandstone block the size of a steamer trunk, is to be flown out by helicopter next month.
The find is expected to yield new clues about dinosaurs' origin. The creatures thrived on earth for more than 150 million years and disappeared -- for reasons still in dispute -- 65 million years ago. In particular, the bones could add new insights into the mysterious transition period from the age of more primitive reptiles, particularly ``thecodonts,'' to the reign of the dinosaur. Thecodont reptiles had legs that extended from the sides of their bodies, as crocodiles and lizards do today. Dinosaur limbs were directly under their bodies, allowing them to support heavier bodies.
Most important, though, the bones may provide new glimpses of what this area looked like eons ago. At the time, there were no flowers, no birds, and virtually no colors -- only green and brown. The first mammals were 10 million years off. Arizona then resembled a tropical jungle, cloaked in towering trees and ferns.
By studying these bones, together with other plant and animal fossils in the forest, scientists can begin to reconstruct the world in which early dinosaurs lived.
``The real significance isn't an isolated dinosaur skeleton,'' says Robert Long, a paleontologist at Berkeley who headed the team. ``But it's that the Petrified Forest has yielded so much about the past. We are able to take the oldest dinosaur and place it in its environment.''