A retired pastor and his son unearthed the skull and lower jaw of a sea reptile believed to be about 70 million years old, Montana State University said.
The find northeast of here represents the first complete skull of a long-necked plesiosaur discovered in Montana, and one of the best specimens of its kind in North America, university researchers said.
"It's a very important specimen," paleontologist Jack Horner said. "We have been looking for it for a long, long time."
Ken Olson of Lewistown said he and his son, Garrett, found the fossils in mid-August about 75 miles (120 kilometers) northeast of Lewistown on Bureau of Land Management property.
Because Horner was out of the country, Olson prepared the fossils himself and delivered them to Horner about three weeks later. The bones now rest in boxes at the Museum of the Rockies in Bozeman. Olson has long collected fossils for the museum.
Horner said the head of a short-necked plesiosaur has been found in Montana, but he had been waiting for the discovery of a complete, long-necked plesiosaur skull. Both ancient sea reptiles lived in the time of dinosaurs, according to Montana State University.
"This critter is one of the long, ridiculously long-necked plesiosaurs" and could have had as many as 70 vertebrae in its neck, said Pat Druckenmiller, an MSU specialist in marine reptile fossils. "If the skull is 40 centimeters [15 inches] long, the neck could be seven to 10 times that length."
Druckenmiller is in charge of examining the bones, and planned to look at them with a CT scanner at Bozeman Deaconess Hospital. He hopes his research will help him better understand the creature's diet and why it needed such a long neck.