Jack Horner, co-author of the study in the September issue of the Journal of Vertebrate Paleontology, and curator of paleontology at Montana State University's Museum of the Rockies, said the nearly-complete skeleton was found way back in 1983, but was located in extremely hard rock, and so took a long time to prepare.
He said he waited for about two decades before lead author Brenda Chinnery, a former potdoctoral researcher with Horner, identified the fossil.
Chinnery had worked for one of Horner's colleagues at Johns Hopkins University and then came to MSU.
"I knew it was probably a new dinosaur, but it took someone that really knew what they were doing to be able to describe it," Horner said.
The dinosaur would have weighed 30 to 40 pounds, walked on two feet and stood about three feet tall.
Horner said the dinosaur, nicknamed Cera, was named Cerasinops hodgskissi after landowner Wilson Hodgskiss, who allowed the scientists permission to collect the skeleton for the Museum of the Rockies.
The fossil was found about five miles south of Choteau, in a different area than the famed Egg Mountain site.
It dates to the early part of the Late Cretaceous Period, and came from sediment about 80 million years old.
Horner said the dinosaur fossil has been stored in the Museum of the Rockies since its discovery, but it will be displayed this winter. The skeleton has a reddish tinge because some of the original bone was replaced by jasper, he said.
Horner said the C. hodgskissi is a simple specimen that it's hard to describe in terms of distinguishing characteristics.
Tests have, however, shown that it represents a very primitive species that shares characteristics of Neo-ceratopsian dinosaurs in North America and Asia. Ceratopsian dinosaurs have horns, but these do not, he added.