Dinosaurs were in Nate Murphy's bones. His grandmother , Nelda Wright, earned a degree in paleontology from Harvard University and was one of the first females in the country to enter the field. Her husband, Clifford Price, got his paleontology degree from the University of Chicago.

In 1967, when he was 11, Murphy joined his grandparents on a dinosaur dig in Canada. His grandparents were nearing retirement at the time so Murphy never got another chance to work with them in the field, but he got rare opportunities to take part in other digs through their contacts in the relatively small world of paleontology.

''They just greased the skids and I got to participate," he said.

From 1968 until 1975, Murphy spent summers working on programs with universities, foundations and museums. He worked on digs in New Mexico and Canada, among other places, and spent some time at the famous La Brea Tar Pits in Los Angeles.

Murphy was born in Southern California, and moved to Alaska when he was 12 with his mother and stepfather. After high school, he went right to work, using the skills he learned on digs to do geology for British Petroleum on Alaska's North Slope.

He never did go to college. Like Jack Horner, Montana's most famous paleontologist, Murphy also contends with dyslexia. ''It's a real curse," Murphy said. ''For me to sit down and type a paragraph -- it takes me quite a while."

After working as a geologist, he drifted away from his passion for the prehistoric world. He put in several years doing session and concert work as a guitarist in Seattle, including a year and a half touring with Country Joe and the Fish.

He also started a cleaning business and before long was making a good living at it, ''although it was just that," he said, ''a means to make a living. It wasn't a passion."

He ended up in Montana because his wife, Nancy, was originally from Saco and wanted to go home. They moved to Whitefish and later to Great Falls, with Murphy still running his cleaning-restoration business.

Over the years, he made many deer-hunting trips to the scrubland plain north of Malta, after which he would often tell friends and family members, ''Man, this area up here is just prime dinosaur country."

In the meantime, he kept up with professional journals and scientific papers in paleontology. Then, in 1992, after years of dreaming about a return to the science he learned from his grandparents, Murphy made the leap.

He sold his half of the cleaning business to his partner, started a new business that would distribute cleaning supplies and moved to Malta. He approached the Phillips County Museum about opening a paleontology wing, and officials there were receptive. At the time, Murphy said, the museum had two or three lichen-covered fossils labeled simply ''dinosaur bones."

Murphy started looking for more bones, doing his first digs on land that had once been part of his in-laws' ranch. His father-in-law had told him that one coulee in particular held a lot of fossils.

''Sure enough," Murphy said, ''there were just bone fragments lying all over the hillside."

Unfortunately, they were fragments, ''kind of like a wrecking yard with disassembled cars," Murphy said. ''We had fenders and bumpers, but nothing substantial to work with."

Murphy began devoting more and more of his time to field work. He found a partner, Bill Hasch, to run his Billings-based business. ''It's let me loose and cut me free," Murphy said.

From the beginning, Murphy gave presentations on his work at schools in the Malta area. Teachers liked his programs, but many of them said they were afraid to teach their students about dinosaurs, since the children usually knew more than they did. Murphy began taking teachers on digs with him, letting them learn paleontology on the ground.

It proved so popular that teachers were soon asking to bring non-teacher friends along. ''I let a few come and then everything broke open," Murphy said.

Since the county museum and historical society were supportive but hardly able to give him any financial backing, Murphy formed the Judith River Dinosaur Institute and started allowing people to pay for the chance to take part in digs. So, for six or seven weeks a year, he takes on 40 to 60 people for five-day stretches of working in the field. Many people have come back year after year, and some of them have become valuable assistants.

''I don't run a paleo-dude ranch," Murphy said. ''I want people who are serious about it and want to learn something from it."

The institute's name is derived from the Judith River formation, the sedimentary layer that contains fossils from the late Cretaceous period, 89 to 65 million years ago.

Tim Quarles, an environmental consultant from Billings, signed up for his first dig five years ago, paying $800 for a one-week program.

''I tell you, it's worth every penny," Quarles said. ''It's a life-changing experience for a lot of people. There' s nothing like being the first person to lay your eyes on something that's been buried for 77 million years."

Quarles hit it off with Murphy, and after completing his stint in mid-July he returned to the dig off and on for the rest of the summer. He returned to work for five weeks the next summer and has been going back ever since. Over the winters, he's gone to Malta many times to help prepare specimens in the field station, or he sorts and identifies fossil fragments in his spare time in Billings.

Quarles said he sometimes wonders how he was so lucky. Here he is, with no formal training in the field, working on projects that ''other people in the profession can' t even dream about. If life was fair, I wouldn't be the one doing it."

Quarles said Murphy's greatest gift is his ability to see a few pieces of bone sticking out of the ground and to visualize the three-dimensional setting of the entire fossil, which helps prevent excavators from damaging the finds.

''The way you stay out of trouble is to know how it's lying and what you're getting into," Quarles said.

If Murphy knows how to look for dinosaurs, he also knows how to look like a dinosaur hunter. He is a big, energetic man, quick to smile and eager to talk. He looks perpetually ready for a dig, favoring a straw hat, hiking boots and shorts. He said it has to get really cold, maybe below zero, before he'll put on long pants.

Hans-Dieter Sues, curator of vertebrate paleontology at the Carnegie Museum of Natural History in Pittsburgh and president of the Society of Vertebrate Paleontology, said Murphy is part of an old tradition in the field.

''There have always been outstanding avocational fossil collectors like Nate, both in the United States and in foreign countries," Sues said. ''Indeed, paleontology remains one of a handful of scientific disciplines where a person without any academic training can make enormous contributions."

In 1996, working in the drainage that would later yield Leonardo, Murphy's prize specimen, his crew discovered Elvis, an adult brachylophosaurus that was complete except for a few feet of tail. Working with staff from the Museum of the Rockies, the specimen was unearthed and taken to the Bozeman museum for study and preparation. After casts were made of Elvis, the original fossil was returned to Malta for display in the Phillips County Museum.

To hold the specimens in public trust, Murphy formed the nonprofit Judith River Foundation, run by a board of directors and scientific advisory board. Using grants and money made by taking people on digs, the foundation opened the Dinosaur Field Station last May in Malta.

The 3,500-square-foot station, located in an old tire shop near the train tracks that cut through town, is a working laboratory, not a museum, though it does offer tours. Everything prepared at the field station will eventually be displayed at the county museum. Murphy said the museum eventually will have to build an addition or a stand-alone dinosaur facility.

Among the institute's significant finds have been two other fully articulated brachylophosaurus specimens -- Roberta, an adult, and Peanut, a very young dinosaur -- and a stegosaurus and a new kind of sauropod, both of which have yet to be fully excavated.

In working with unusually complete specimens, Murphy has pioneered an excavation method that involves resting the entire fossil on a steel frame and wrapping it in many layers of plaster, then using a huge crane to remove the specimen in one piece.

Leonardo weighed 13,000 pounds when he was hoisted out of the ground, what with the weight of the fossil, the steel, the plaster and the rock that was left around the fossil to preserve it until it reached the field station.

Among the crew working on Leonardo was Murphy's most stalwart assistant over the years, his son, Matt, now 19. He has been working with his father since he was 6 years old.

Matt, who was home-schooled, is still working for the institute and has helped his father write scientific papers. He said he has had several offers from universities, but hasn't made his mind up yet what he wants to do.

''I've tried not to push him," Nate Murphy said. ''He loves it. He's just like me."