November 9, 2012
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.
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
March 2, 2012
One of my favorite dinosaurs at the American Museum of Natural History is the Styracosaurus. The insanely ornamented creature is presented as if swimming through a wave of plaster, a pose meant to depict the way the dinosaur was found in the field. It is a beautiful mount, but the restored and reconstructed skeleton obscures the fact that the actual specimen is not so complete.
Veteran fossil hunter Barnum Brown discovered the Styracosaurus in 1915. He found the fossil within what is now Canada’s Dinosaur Provincial Park. Most of the dinosaur’s post-cranial skeleton was intact, but as Brown later noted in a 1937 paper he wrote with colleague Erich Schlaikjer, only a few parts of the skull were recovered. That lovely skull on the AMNH mount was mostly reconstructed on the hypothesis that the animal was really a Styracosaurus. Brown believed that the few parts which were collected were enough to name a distinct species of this dinosaur: Styracosaurus parksi.
Brown’s new species was the third flavor of Styracosaurus to be named. Paleontologist Lawrence Lambe named the first species, Styracosaurus albertensis, in 1913, and Charles Gilmore followed with Styracosaurus ovatus in 1930. Both were very spiky dinosaurs distinguished by the prominent spikes jutting out of the parietal bones on their frills. But Brown considered his dinosaur to be a separate species on the basis of slight differences in the few skull elements he had collected. The squamosal bone—another frill element—seemed to be longer and different in shape than the animal Lambe had named Styracosaurus albertensis.
Early 20th century paleontologists had a tendency to over-split dinosaurs on the basis of very slight differences. Naming a new genus or species was easy to justify during the early bone rushes. There were so few specimens, and researchers understood so little about how dinosaurs grew up, that variations among individuals or differences attributable to age were often taken as the hallmarks of distinct species. And traits thought to distinguish between dinosaur genera turned out to be less diagnostic than originally thought. Styracosaurus once seemed to be unique in having spiky parietals, for example, but similar features have since been found in closely related centrosaurine dinosaurs such as Achelousaurus, Einiosaurus, Centrosaurus brinkmani, Pachyrhinosaurus and, the new kid on the block, Spinops. In order to sort out Styracosaurus, in 2007 paleontologists Michael Ryan, Robert Holmes and A.P. Russell reviewed the material attributed to this dinosaur.
Ryan, Holmes and Russell counted only two Styracosaurus species as valid: S. albertensis and S. ovatus. Brown’s specimen, while incomplete, fell within the variation documented for S. albertensis, and so S. parksi was sunk. And at the genus level, Ryan and co-authors distinguished Styracosaurus from similar dinosaurs by the anatomy of the ornaments at each slot on the parietal part of the frill. The first ornament is typically a tiny nub, the second either appears as a small tab or hook, the third is a large spike and the fourth is also a large spike. (The remaining ornaments at positions five through seven vary in size and shape between individuals.)
But the Styracosaurus genus was recently winnowed down even further. Most Styracosaurus specimens belonged to the northern species S. albertensis, but the species S. ovatus was represented by a single specimen found in Montana. This significantly extended the range of Styracosaurus, at least until paleontologists Andrew McDonald and Jack Horner suggested in 2010 that the Montana dinosaur really represented a different genus. On the basis of the partial frill and other skull fragments, they named the dinosaur Rubeosaurus. It was another weird horned dinosaur with a huge nasal horn, and the third parietal horns were directed inward, towards each other, rather than outward like in Styracosaurus. Within just a few years, three species of Styracosaurus were cut down to just one.
Brown, B., Schlaikjer, E. 1937. The skeleton of Styracosaurus with the description of a new species. American Museum Novitates. 955, 1-12
Andrew T. McDonald & John R. Horner, (2010). “New Material of “Styracosaurus” ovatus from the Two Medicine Formation of Montana”. Pages 156–168 in: Michael J. Ryan, Brenda J. Chinnery-Allgeier, and David A. Eberth (eds), New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium, Indiana University Press, Bloomington and Indianapolis, IN.
Ryan, M., Holmes, R., Russell, A. (2007). A revision of the late campanian centrosaurine ceratopsid genus Styracosaurus from the Western Interior of North America
Journal of Vertebrate Paleontology, 27 (4), 944-962 DOI: 10.1671/0272-4634(2007)27[944:AROTLC]2.0.CO;2