New Horned Dinosaur Had a Funky Frill

Ceratopsids were flashy dinosaurs. These herbivorous heavyweights were adorned with horns, spikes, hooklets, and bosses that came in a stunning variety of shapes and arrangements, making them look just as sexy to paleontologists searching for new species as the dinosaurs must have looked to their own kind. And despite over a century of research on these animals, researchers are continuing to find ceratopsids that push the boundaries of cranial ornamentation. The latest to be named, Mercuriceratops gemini, had a frill unlike any other.

As with most dinosaurs to make headlines, the 77 million year old Mercuriceratops is only known from fragments. All paleontologists have of the dinosaur are two right squamosals – broad bones that made up the side of the dinosaur’s big frill – that were found over 230 miles away from each other, one in Canada’s Dinosaur Provincial Park and the other in Montana’s Judith River Formation.

The two known fossils of Mercuriceratops, showing their position on the frill. Image from Naturwissenschaften.
The two known fossils of Mercuriceratops, showing their position on the frill. Image from Naturwissenschaften.

For any other ceratopsid, attributing isolated squamosals to a particular species is a difficult task. That’s because squamosals retain very similar shapes across species, only showing major differences in the two major subdivisions of ceratopsid dinosaurs. In the centrosaurines – dinosaurs like Centrosaurus and Styracosaurus – the bone is roughly rectangular, while chasmosaurines such as Chasmosaurus had longer, triangle shaped squamosals. But the extra ornamentation on the frill of Mercuriceratops showed paleontologist Michael Ryan and his coauthors that they had found something new.

Mercuriceratops had squamosal “wings.” Instead of a smooth squamosal margin, typical of other ceratopsids, this newly-named dinosaur had a flaring, rounded tab of bone jutting from the squamosal that was decorated by little horns around the edge. This is how the dinosaur got its name, a nod to the winged helmet of the Roman god Mercury (while the species name honors the twins Castor and Pollux of Greek mythology, a reference to the “twin” squamosals found in Alberta and Montana). The shape of the squamosal shows Mercuriceratops was a chasmosaurine, but this dinosaur was unlike any other species yet found.

But now we’re faced with that classic fossil quandary – “Where’s the rest of it?” Other bonebeds of roughly the same age haven’t turned up any additional, definitive Mercuriceratops specimens. And now that this dinosaur is named on the basis of a single part of the skull, paleontologists will have to find a skull with a distinctive squamosal wing to be sure they’ve really found another Mercuriceratops. That’s going to take a lot more digging. The oldest chasmosaurine dinosaur found in Canada to date, Mercuriceratops was apparently a rare dinosaur that did not leave as much behind as its contemporaries. Only more sweat-soaked time scouring the badlands will fill in the skeletal gaps.

Reference:
Ryan, M., Evans, D., Currie, P., Loewen, M. 2014. A new chasmosaurine from northern Laramidia expands frill disparity in ceratopsid dinosaurs. Naturwissenschaften. DOI 10.1007/s00114-014-1183-1

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