Laelaps

Eotriceratops xerinsularis!

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A close-up of the Triceratops mount on display at the AMNH.

Blogging on Peer-Reviewed ResearchOrnithischian 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.

Comments

  1. #1 Zach Miller
    November 29, 2007

    The Diceratops pairing with Torosaurus made no sense to me, although it’s not like I have access to a phylogeny computer program. Now that I actually think about it, “two-horned face” does share the bull lizard’s vertically-oriented supraorbital horns, but the snout is short, as is the frill, like in “three-horned face.”

    At any rate, I was extremely disappointed that the Eotriceratops paper did not include a skull reconstruction. That photo on my blog is okay, but the angle is awful and the frill is missing the unusual epoccipital “scutes” which differentiate Eotriceratops from other chasmosaurines. That is, the little bumps or spikes that frame the frill of other ceratopsians are long and spindle-shaped in Eotriceratops, a feature the authors assert is a diagnostic trait of the taxon.

    One more thing: The paper didn’t really mention whether Eotriceratops had any kind of fenestrae in the frill. The frill is hidiously incomplete, sure, but the reconstruction (in that photo) lacks frill windows. I would like a justification for that.

  2. #2 Traumador the Tyrannosaur
    November 29, 2007

    It’s a really remarkable skull… I worked at the Tyrrell through the period of them perparing and casting it… It’s HUGE… not quite Pentaceratops or Torosaur, but compared to normal Albertan Ceratopsians.

    I have a kinda funny but embrassing story with this specimen.

    I was working on casting a Corythosaur for an education program the same year they were making the replica of this skull (though it hadn’t been named yet and was just the Horseshoe Triceratops back than, much like Albertoceratops being worked on in the main lab during this same period of time that was the Dino Park Pacyrhino). As an outsider non technican (and merely an energetic zany educator) I was looked upon as a bit of an outsider while working in the lab due to the standard norm of educators and techs never mixing at work. I didn’t really mind as I learned a ton from the experience and it was cool working in the casting lab though while they were finishing up the Eotriceratops replica.

    The casting lab was SMALL though. I had half of it for my duckbill, and the Eo literally took up the other half, and than some! The two techs who normally worked on the molding were small, and could navigate the tight space with ease. This included walking underneth the eye horn which hung over the only clear floor space we had to walk in. I however at 2 metres tall was at the perfect height to be clothes lined by the thing if I wasn’t careful. Which of course you can see where this story is going.

    Having gotten some Palaeobond glue on my hand by accident (it’s super super glue if you haven’t used it) I needed to get the solvent quick to prevent a painful attaching of my thumb to the side of my hand. In my haste, and being further down my table than normal I caught the Eo’s horn right on my throat as I moved at high speed. Both techs were in the room, and I was aware of both of them stopping breathing as I ran into the last 3 years worth of their work. Rather than keep my dignity, but possibly break what now turns out to be a new dino I did a stage drop. Which basically meant I fell to the floor backwards so my legs shot out under the horn, but draged my torso away and landing nearly square on my back (hurting myself a bit in the process). Though they mocked me for glueing myself the casting techs from there on in gave me a lot more respect, after a fashion, due to my attempt to save the Eo over myself (and the amuzement of seeing a lowly educator willingly make a fool of himself for their benefit).

    Dumb story I know, but it’s what I associate with Eotriceratops. Big horn that hits you in the neck perfectly… Though in fairness it’s a really thick horn. I don’t think I coulda ripped it off unless I really tried.

  3. #3 Nagi
    December 1, 2007

    “…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).”

    As an unusually huge fan of Albertosaurus (for whatever reason, the idea of a slimmer, speedier variant of T.rex that was quite possibly gregarious fascinates me), I greatly anticipate this blog. 🙂

  4. #4 Hai~Ren
    December 1, 2007

    I can never get enough of ceratopsids. To me, they’re one of the coolest dinosaur groups out there, even if they were restricted to western North America, and had a temporal range of probably somewhere around only 20-30 million years. But wow… the sheer diversity of forms they had in the Campanian and Maastrichtian is stunning.

    One thing I realised is that Eotriceratops xerinsularis is the first new genus and species of ceratopsine/chasmosaurine to be named, since Arrhinoceratops brachyops was described in 1925. Of course, since then and now, new genera have popped up (Agujaceratops to accommodate the former Chasmosaurus mariscalensis), and new species have been coined (e.g. Chasmosaurus irvinensis), but Eotriceratops is the first ceratopsine taxon to be given its own genus and species in a long time.

  5. #5 Zach Miller
    December 1, 2007

    I wouldn’t say that, Hai. Albertaceratops was named this year, and Jim Kirkland found another basal centrosaurine (with long brow horns) last year that still doesn’t have a name. And there’s been a lot of new animals named in the pre-Ceratopsidae clades.

  6. #6 Hai~Ren
    December 2, 2007

    Zach: You’re correct, but I meant that Eotriceratops is the first new chasmosaurine taxon to be given its own genus and species since 1925. (Not counting the moving of Chasmosaurus mariscalensis over to Agujaceratops)

    Which is entirely correct as well. =)

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