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Evolution Of Horned Dinosaurs Revealed By Skelton of Baby Chasmosaurus

Jan 14, 2016 05:07 PM EST
Baby Chasmosaurus
Fossils of a baby Chasmosaurus indicate juvenile dinosaurs had smaller and narrower bony head appendages -- or frills -- than grown adults.
(Photo : Michael Skrepnick)

Dinosaur fossils belonging to a baby Chasmosaurus originally unearthed in 2013 have shed new light on some evolutionary mysteries. Paleontologists from the University of Alberta say this rare find has revealed interesting characteristics and fills in some ancestral gaps of horned dinosaurs, including the well-known Triceratops.

"For the first time ever, we have a complete skeleton of a baby ceratopsid," Professor Philip Currie, one of the study researchers, said in a news release.

The intact skeleton of the juvenile Chasmosaurus, nicknamed 'chasm', suggests the animal was only three years old when it died, perhaps from drowning, researchers say. What is unique about this find, however, is that the baby dinosaur's bones had remained fully intact 75 million years after it died.  

"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," Currie added. "All you need is one specimen that ties them all together. Now we have it!"

The fossil specimen is roughly 1.5 meters long, but would have grown to five meters, had it reached adulthood.

"One of the greatest benefits is that we can now look at the different body proportions for Chasmosaurus as it grew up," Currie explained. "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."

An adult Chasmosaurus typically had three short horns on its face and a large bony plate - or frill -projecting from the back of its skull. Therefore, researchers expected to find that the baby had a short frill, proportionate to its skull. However, they were surprised when they found the baby's frill was also shaped differently.

"Unless you've got that basic anatomical information, you're kind of shooting in the dark with all of these other calculations," Currie said in the university's release.

"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. 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 added. "It is very different than I expected."

Next, Currie plans to analyze the brain case using advanced CT scanning in Japan.

"We still haven't plumbed the depths of the anatomical description," Currie said, noting that this Chasmosaurus specimen holds 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.

Their study was recently published in the Journal of Vertebrate Paleontology.

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