Eotriceratops xerinsularis!

Ornithischian dinosaurs don't often get much attention, perhaps because some groups (i.e. hadrosaurs) are often viewed as the "cows" of the Mesozoic, having almost the exact same body plan only differing in head ornamentation. Members of the family Ceratopsidae often have better publicists, though, Triceratops being one of the most recognized and popular of dinosaurs despite public unfamiliarity with many other ceratopsids.* It might come as a bit of a surprise, then, to learn that a new ceratopsid closely related to Triceratops has been found in deposits slightly older than "three horned face" in a place where no large chasmosaurines have previously been known, and this creature is known as Eotriceratops xerinsularis.

Discovered by a cook during a systematic study of the dinosaurs of the Horseshoe Canyon Formation, Eotriceratops came as a bit of a surprise to researchers in 2001, especially since this fossil was apparently passed up by Barnum Brown ("Mr. Bones") himself. In 1910 Brown was collecting fossils from this area and seemingly passed over the fossils that are now known as Eotriceratops because of their poor quality compared to some other specimens in the area, assemblages that included the intriguing Albertosaurus bone bed (a topic that I will blog about again when discussing social habits of theropods at another time). What is trash to one bone sharp is treasure to others, though, and Eotriceratops is certainly a significant find.

Part of the difficulty with ceratopsid dinosaurs is that their fossils are biased towards the preservation of skulls (contrast this with sauropods that often lose their heads after death), postcranial elements often being missing or difficult to use if they're not associated with a skull given the similarity of body plans between horned dinosaurs. So it is with Eotriceratops, where the majority of the remains are parts of the skull with a few vertebrae, ribs, and ossified ligaments associated. Before moving on to a discussion of these remains, though, it should be noted that this dinosaur has been placed at about 67.6-68 Ma, making it perhaps the oldest known large chasmosaurine when compared to the deposits bearing Triceratops fossils in the Scollard, Frenchman, Hell Creek, and Lance Formations while being younger than any ceratopsid known from the Horseshoe Canyon Formation, putting it in an important biostratigraphic and evolutionary position.

What is immediately striking about the skull of this animal, though, is the sheer size of it; based upon the available elements the authors estimate that the skull measured about 3m long! In addition to this large size and height of the premaxilla, further distinguishing it from Triceratops and other dinosaurs. (See Zach's blog for a photo of a reconstruction of the skull of Eotriceratops.) What allies this dinosaur with more "crownward" members of chasmosaurines is the fact that its orbital horns are positioned more posteriorly (or slightly behind the orbit) than in chasmosaurines like Pentaceratops, a synapomorphy this dinosaur shares like Triceratops, Torosaurus, and Arrhinoceratops. When phylogentic studies were carried out, however, Eotriceratops appeared to form a monophyletic grouping with Torosaurus and Diceratops being more closely related to each other, Eotriceratops itself either being a sister group to Triceratops or being the most basal member of the group, the exact positioning of this dinosaur remaining a somewhat enigmatic.

There's something else about the skull that should draw our attention, however, and that's several punctures interpreted as bite marks on the postorbital bone just above the eye near the base of the horn core. There appear to be (based on the reconstruction) two indentations that are close together and then another a few centimeters away, making it difficult to determine just what was biting the skull of this animal and how it was doing it. Indeed, even the placement of the bite is strange as I wouldn't imagine that there is a lot of good eating on an Eotriceratops skull for a large theropod, so while it could be said that the bite marks are a result of scavenging I don't know why a scavenger would bite this dinosaur at the base of one of its orbital horns. Given that, it's more difficult to see why a theropd would bite a live Eotriceratops at the base of a horn unless it occurred during a fight, but such a scenario doesn't have any positive evidence either. Whatever happened is likely to remain a mystery, though, and the most that I can say is that there appear to be bite marks on the skull.

So there you have it; a new chasmosaurine that fills in a biostratographic gap and may fill an evolutionary gap as well (or maybe represents another part of the late Cretaceous radiation of these dinosaurs). Hopefully, now that Eotriceratops has been identified, more enigmatic parts that have been overlooked in the field or in museum storage can be reexamined to determine if more specimens might be hiding in plain sight elsewhere. Still, just like nearly any fossil, Eotriceratops poses more new questions than delivers answers, but at least now fossil hunters have something else to keep their eyes peeled for. This year alone has seen many fascinating new announcements, and I can hardly wait to see what 2008 is going to bring.

*Just like Darren recently noted that Stegosaurus was the oddest of the known stegosaurs (even though it is one of the most popular dinosaurs), so too is Triceratops strange even when compared to other chasmosaurines like Torosaurus. Much of the difference has to do with the frill of Triceratops, which is much relatively much shorter compared to the size of the skull than other chasmosaurines, as well as the fact that the huge holes present in the frills of other ceratopsians are absent in Triceratops (Dodson 1996, p. 57). Diceratops is also mentioned as being a member of this group, but whether Diceratops is a valid genus or not has been disputed, interpretations of the Diceratops skull in question sometimes being referred to Triceratops and other times inferred to actually represent a specific genus. In the Wu et al. paper, though, Diceratops is considered valid and closer to Torosaurus than to Triceratops within a monophyletic clade containing Triceratops, Torosaurus, Diceratops, and Eotriceratops.

References;

Dodson, P. (1994) The Horned Dinosaurs. Princeton University Press, NJ.

Wu, X-C., Brinkman, D.B., Eberth, D.A., Braman, D.R. (2007) "A new ceratopsid dinosaur (Ornithischia) from the uppermost Horseshoe Canyon Formation (upper Maastrichtian), Alberta, Canada." Canadian Journal of Earth Sciences 44: 1243-1265.