Paleontologists Welcome Xenoceratops to the Ceratopsian Family Tree

 

A restoration of Xenoceratops by Danielle Dufault, courtesy David Evans.

It’s a good time to be a ceratopsid fan. Since 2010, paleontologists have introduced us to a slew of previously unknown horned dinosaurs, and new discoveries are continuing to trickle out of field sites and museums. Long-forgotten specimens and unopened plaster jackets, especially, have yielded evidence of ceratopsids that researchers overlooked for decades, and this week Royal Ontario Museum paleontologist David Evans and colleagues have debuted yet another horned dinosaur that was hiding in storage.
The Late Cretaceous exposures of Alberta, Canada’s Belly River Group are rich with ceratopsid fossils. For over a century, paleontologists have been pulling bones of the fantastically ornamented dinosaurs from these badlands. Yet most of the ceratopsids from this area have been found in the Dinosaur Park Formation, and researchers have paid less attention to the older strata of the Oldman and Foremost Formations nearby.
The Foremost Formation, in particular, has received little attention because diagnostic dinosaur remains seem to be rare within its depths, but a few notable specimens have been found in this slice of time. In 1958, paleontologist Wann Langston, Jr. and a crew from what is now the Canadian Museum of Nature pulled fragments of several ceratopsid specimens from 78-million-year-old deposits in the Foremost Formation. Those bones and skeletal scraps sat in collections for years until they caught the eye of Evans and Michael Ryan (the lead author of the new study) as they made the research rounds for their Southern Alberta Dinosaur Project. Although fragmentary, Langston’s fossils were from a new genus of ceratopsid.
Evans, Ryan and Kieran Shepherd have named the dinosaur Xenoceratops foremostensis in their Canadian Journal of Earth Sciences study. The dinosaur’s name–roughly “alien horned face”–isn’t a testament to the ceratopsid’s distinctive array of horns but to the rarity of horned dinosaur fossils within the Foremost Formation. Indeed, despite Danielle Dufault’s gorgeous restoration of the dinosaur, Xenoceratops is presently represented by skull fragments from several individuals. The researchers behind the new paper pieced them together to create a composite image of what this dinosaur must have looked like, and, in turn, discern its relationships.

Based upon the anatomy of one of the dinosaur’s frill bones–the squamosal–Evans and coauthors are confident that Xenoceratops was a centrosaurine dinosaur. This is the ceratopsid subgroup containing other highly decorated genera such as Styracosaurus, Spinops, Centrosaurus and another dinosaur given a new name in the same paper, Coronosaurus (formerly “Centrosaurus” brinkmani). The other ceratopsid subgroup, the chasmosaurines, encompass Triceratops, Torosaurus and other genera more closely related to them than Centrosaurus.
At approximately 78 million years old, Xenoceratops is currently the oldest ceratopsid known from Canada, beating out its cousin Albertaceratops by half a million years. Given the age of Xenoceratops, and the fact that it had long brow horns and a short nasal horn, instead of the long nasal horn-short brow horns combo seen in its later relatives, it isn’t surprising that the dinosaur seems to be at the base of the centrosaurine family tree. This means that Xenoceratops can help paleontologists examine what the early members of this significant ceratopsid group were like and how drastically centrosaurine ornamentation changed. “Xenoceratops has very well developed frill ornamentation comprised of a series of large spikes and hooks, occurring at multiple parietal loci, that foreshadows the great diversity of these structures in other species that occur later in the Campanian,” Evans says, and this indicates that “complex frill ornamentation is older than we may have thought.”

Still, Evans cautions that Xenoceratops is presently a very scrappy dinosaur. We need more fossils to fully reconstruct this dinosaur and confirm its place in the ceratopsid family tree. The dinosaur’s “true significance in terms of ceratopsid origins will only be revealed with further discoveries,” Evans says, particularly between the time of the slightly older Diabloceratops found in southern Utah, and the even more archaic, roughly 90-million-year-old ceratopsian Zuniceratops. “Our record of ceratopsians in this critical part of their family tree is still frustratingly poor,” Evans laments. In fact, paleontologists know relatively little about dinosaur diversity and evolution during the middle part of the Cretaceous–a critical evolutionary time period for ceratopsians, tyrannosaurs and other lineages that came to dominate the Late Cretaceous landscape. If we are ever going to solve the mystery of how ceratopsids evolved, and why they were such garishly adorned dinosaurs, we must search the lost world of the mid-Cretaceous.
References:
Ryan, M., Evans, D., Shepherd, K. 2012. A new ceratopsid from the Foremost Formation (middle Campanian) of Alberta. Canadian Journal of Earth Sciences 49: 1251-1262