A Brigham Young University geology student has discovered pieces of an embryo and eggshell believed to belong to the 135- to 150-million-year-old Dryosaurus dinosaur.

The find is significant, because no dinosaur eggshell as old with this advanced embryo (near hatching age) has been reported in North America, according to Wade Miller, geology professor and director of the BYU Earth Science Museum."Any dinosaur embryo is rare and important," said Miller. "This discovery helps us study dinosaurs at early stages, a major gap in our knowledge of dinosaur development."

Miller's student, Rod Scheetz, discovered the embryonic fossils in May while working with the Museum of Western Colorado near Uravan, an area west of the BYU Earth Science Museum's Dry Mesa dinosaur quarry in southwestern Colorado.

Among his findings were vertebrae and jaw fragments showing two erupting teeth, each a little more than a millimeter wide. The skeletal elements appear to be well-developed in both teeth and vertebrae, which indicates that the dinosaur was ready to emerge from its shell.

"The teeth have not even erupted fully from the jaw and show no wear, an indication to us of its embryonic stage," agree Scheetz and Miller.

Scheetz found the embryo among other fossils of more mature individuals of the same type of dinosaur scattered on a mound in the Morrison Formation. Also included in the pile were eggshells, unidentified plant matter and other bone fragments.

Fragments found at the site indicate eight sizes of juvenile fossils.

"It's also rare to find a juvenile site," says Miller.

The area had been damaged by a bulldozer creating a road, which Scheetz initially found upsetting until he speculated that the embryo may not have been found had it not been pushed above ground.

Preliminary estimates by Scheetz show that 80 percent of the bones are from Dryosaurus with some others being crocodilian and mammalian in appearance.

"The area has the potential of being a nesting site," says Miller and Scheetz. "We're excited to do more work in the area."

Dryosaurus, first discovered in 1876, has been compared with the modern gazelle because of its slender build and long, agile hind limbs. A herbivore with teeth, Dryosaurus is a member of the hypsilophodontids, a family of small- to medium-sized dinosaurs.

The dinosaurs grew between 10 to 13 feet long and had long, powerful hind legs and strong arms, each with five fingers. Their stiff tails could have been used for balance when the animals ran.

They were also characterized by sharp ridged cheek teeth and probably nipped vegetation off with a bony beak and chopped leaves and shoots with its cheek teeth. A wide-ranging dinosaur, Dryosaurus remains have been found in North America and East Africa.