Everyone knows Triceratops. The herbivore’s a Cretaceous celebrity. Over the past ten years, however, old “three horned face” has started to look increasingly vanilla. One by one, paleontologists have uncovered a slew of massive horned dinosaurs with even flashier arrays of horns on their noses, over their eyes, and around their frills. Diabloceratops, Medusaceratops, Kosmoceratops, Coronosaurus… the list goes on. In fact, today another spiky titan is added to the list, and this new dinosaur was an evolutionary copycat.
The ceratopsid, described today in Current Biology by Royal Tyrrell Museum paleontologists Caleb Brown and Donald Henderson, was discovered in 2005 by geologist Peter Hews as he walked along the bank of the Oldman River in Alberta, Canada. The Royall Tyrrell took up the job of excavating the 70 million year old dinosaur in 2006 and 2008, but it was a tough spot to work in. “Collection was difficult due to a combination of hard rock, steep cliffs, and proximity to protected fish spawning habitat”, Brown says – all of which led the paleontologists working the site to nickname the dinosaur “Hellboy”.
But all that effort was worth it. Hews’ dinosaur, officially named Regaliceratops peterhewsi, is a strange species that seems to combine traits from the two great lineages of horned dinosaurs.
It breaks down like this. In the Late Cretaceous of North America, there were two horned dinosaur branches – the centrosaurines (such as Centrosaurus, Styracosaurus, etc.) and the chasmosaurines (Chasmosaurus, Utahceratops, etc.). And while the dividing lines have gotten a bit fuzzy with new discoveries, the two can often be differentiated at a distance by their differing horn arrangements. Centrosaurines often had long nose horns, short brow horns, and lots of spiky ornaments around the edges of their short frills while the chasmosaurines often had short nose horns, long brow horns, and smaller ornaments around the borders of their expanded frills.
So where does Regaliceratops fall? “Preparation [of the skull] was difficult, and took around 18 months,” Brown says. It was clear that the dinosaur was new, especially since no horned dinosaurs had been previously been found in the area of discovery, but its anatomy was confusing. “Many visiting researchers had a double-take when they first saw the specimen”, Brown says, because Regaliceratops seemed to combine traits of both chasmosaurines and centrosaurines. Ultimately, though, the anatomy of the dinosaur’s premaxilla – the bone at the front of the upper jaw – allowed Brown and Henderson to conclude that it was a chasmosaurine doing an impression of a centrosaurine. Regaliceratops is a case of dinosaur convergence.
Such resemblances have been seen before. “The hooks on the frill of Kosmoceratops are in many ways almost identical to the individual hooks seen on Centrosaurus,” says Raymond M. Alf Museum of Paleontology’s Andrew Farke, adding “we already knew about animals like Chasmosaurus that had short brow horns and longish nose horns.” But, Farke says, what makes Regaliceratops cool is that it comes out in the chasmosaurine family tree near Triceratops where convergence in horn arrangement hasn’t been seen before.
And the horned herbivore certainly lives up to its regal name. “It has the largest epiossifications [or frill ornaments] of any chasmosaurine, with a halo of these triangular and pentangular processes resulting in a crown-like appearance”, Brown says. Paired with the long nose horn and tiny brow horns, Brown says, this makes Regaliceratops “stick out like a sore thumb” compared to all its close relatives.
Future finds might close the anatomical gap. Regaliceratops was found in a 70 to 68 million year window of horned dinosaur evolution that paleontologists know relatively little about, Farke says. Compared to the few Triceratops-like animals known from that timespan, Farke says, “Regaliceratops is sorta out of left field!” Given that this dinosaur didn’t pop into existence but evolved from earlier ancestors, there must be other peculiar horned dinosaurs waiting to be found that will help researchers envision the dramatic rearrangements of frills and horns these dinosaurs underwent through time. In other words, new discoveries are likely to only make ceratopsids stranger.
Brown, C., Henderson, D. 2015. A new horned dinosaur reveals convergent evolution in cranial ornamentation in ceratopsidae. Current Biology. doi: 10.1016/j.cub.2015.04.041