Paleontologist Bones Up on Life 100 Million Years Ago, Digs for Dinosaur : Arizona: Researcher is racing to finish harvesting a rare find uncovered on a rugged ridge, before the start of rains that could wash away exposed fossils.

Ron Ratkevich, self-described 43-year-old little kid, is mining a fossilized treasure in a remote hillside he wouldn’t trade for gold.

He’s living out his childhood dream, unearthing remains of a potentially new dinosaur perhaps 100 million years old.

“It’s the most complete dinosaur ever found in Arizona,” said Ratkevich, paleontologist for the private, Tucson-based Arizona-Sonora Desert Museum. And it’s in a five-square-mile area he calls “the Valley of the Dinosaurs,” which could hold countless others and will be the subject of future digs.

It has come about, he said, because of “a bit of geological serendipity”--and a stroke of blind luck involving two fossil hunters.

Ratkevich is racing to finish harvesting a number of bones uncovered on a rugged ridge, before the start of summer rains that could wash away exposed fossils.

He estimates about 40% of the skeleton has been recovered, and thinks 70% to 90% could be found after the rains.

The dinosaur probably was a 20- to 27-foot long plant-eater with a bird-like hip that roamed in herds, could walk on its hind legs and used its front legs and bird-like beak to gather plant food.

It had a short neck and a long, whip-like tail and weighed about 4,000 pounds.

Ratkevich said the bones fit none of the creatures the researchers have tried comparing it to.

The site’s location on state land north of Sonoita is being kept secret to deter vandals.

The skull has not been located.

“I don’t have any evidence that we’ll get more than 50%,” said David Thayer, the museum’s curator of geology. “I’m going to be real excited if we have 70%. But 50% is a lot.”

The museum plans a major exhibit eventually, including a full-scale replica of how the skeleton looked when discovered.

The dinosaur will be portrayed in context with its world of about 90 million to 108 million years ago, during the Middle Cretaceous Period--a time not known for its dinosaurs, Ratkevich said.

He and Thayer were to meet with specialists at the American Museum of Natural History in New York to assess the importance of their find.

But they have little doubt.

Nicholas Hotton, research paleontologist emeritus with the Smithsonian Institution in Washington, said it sounds interesting and significant, and probably new to science.

“There’s relatively little from the middle Cretaceous Period, at least on this continent. That’s great,” he said.

The Cretaceous Period began 135 million years ago and ended 65 million years ago, with the extinction of dinosaurs.

Hotton also said the number of bones found is significant. “When you get that much of a skeleton, that’s something to write home about, even as much as they’ve got already.”

The excavation team hopes to name the dinosaur Sonorasaurus, commemorating the museum’s involvement and its location in the Sonoran Desert.

The animal is believed to have died and been carried into a low-lying river channel, near what scientists call the Bisbee Sea.

Sediment preserved the skeleton by covering it quickly. The sandstone deposits now stand vertically, from geological upheaval.

“For some reason or another, just a bit of geological serendipity, this one valley . . . this one little pocket was preserved and hasn’t really been explored,” Ratkevich said. He and his colleagues are calling it “the Valley of the Dinosaurs” because there are clues that more dinosaur bones are weathering out from the entire valley.

Last November, amateur fossil hunters Gordon Nelson and Richard Thompson stumbled across the sandstone ridge. Nelson spotted part of a fossilized pelvic bone, shoulder blade and some ribs. They realized what they had found and contacted the museum.

“We’re just so thankful to them. We’re indebted,” said Ratkevich. “This is truly a state treasure for the state of Arizona.

“I’ve died and gone to heaven--dinosaur heaven. How many people can do what they’ve dreamed of doing since they were a young kid?

“Here I am, middle-aged little kid, digging up a dinosaur.”