One of the rarest dinosaur discoveries - a 75-million-year-old fossil of a juvenile Chasmosaurus - may help fill in gaps in the evolution of other horned dinosaurs, scientists say.

"For the first time ever, we have a complete skeleton of a baby ceratopsid," said Philip Currie from the University of Alberta. "We've only had a few isolated bones before to give us an idea of what these animals should look like as youngsters, but we've never had anything to connect all the pieces," said Currie.

The discovery made in 2010 in Dinosaur Provincial Park in Canada allows for the refinement of previous findings and provides the opportunity to fill in gaps in the evolution of other horned dinosaurs, such as Triceratops, researchers said.

"One of the greatest benefits is that we can now look at the different body proportions for Chasmosaurus as it grew up," Currie said. "We now have an anchor point with the baby that we can compare with all other specimens of this species, and from that comparison can calculate the dimensions, body weights and ages for all other ceratopsid species. We can start filling in missing pieces," he said.

Currie said the findings hold incredible value not only for paleoecological studies, but also for understanding the life history, biomass, population structure, growth rates, variation and physiology of these animals. "Unless you've got that basic anatomical information, you're kind of shooting in the dark with all of these other calculations," he said.

He said the biggest surprises came in the comparisons of shapes and relative proportions with adult Chasmosaurus. "There was no doubt in our minds that a baby would have had a much shorter frill relative to its skull length than an adult. But what we couldn't see is that it also has a different shape," said Currie.

"Now, with a full skull of a juvenile in which the bones actually articulate with each other, we can see that in Chasmosaurus, the back of the frill isn't broad and squared off the same way that it is in an adult," he said. "In fact, the frill narrows towards the back. And instead of being flat on top from one side to the other, the frill is arched and has a ridge running down the middle of it," he said.

"We still haven't plumbed the depths of the anatomical description," said Currie, noting that the specimen will provide scientists with unparallelled opportunities to study the growth, changes and variation of a single species.

The findings were published in the Journal of Vertebrate Paleontology.