Thursday, November 29, 2007

Eotriceratops xerinsularis, Part Deux

Having now read Eotriceratops' paper (thanks again to my loyal readers!), I've got a few complaints about it. First and foremost, there is no skull reconstruction! This could be because the frill is so incomplete, but otherwise there's enough to draw something toward the end of the paper. But no, we just get drawings and photos of individual bones. All I've got to on are two photos of questionable quality from various news sources (the one above is from Discovery News, and it's the best picture I could find).

This is a topic I feel very strongly about. Since there are no living non-avian dinosaurs, it is imperative that paleontologists put some effort into reconstructing an animal when such a reconstruction is appropriate. We don't need an awesome painting by an esteemed paleo-artist accompanying every scientific paper, but a reconstruction of the known parts would help give me an image from which to base my own musings and reconstructions on. Now, there are some taxa which should not be reconstructed (yet). Masiakasaurus is one of them. It's tough to draw an entire animal when the only really informative parts you have are the legs and dentary. Noasaurs are tough enough due to their fragmentary nature, but when you throw a tooth curveball in there, I find it extremely questionable to reconstruct the rest of the bugger's head as pretty normal.
Think about that. What if Masiakasaurus has some sort of ridiculous crest on its head like Guanlong or its sister family, the Abelisauridae? Until more fossils are found, I think that a full reconstruction is premature. Every picture of Masiakasaurus I've seen, by the way, have been essentially based on the original headshot, which appeared on the cover of Nature the week it was described.

Anyway, at the other end of the spectrum, you've got taxa which are known from a lot of good material--certainly enough to warrant a picture of the head, but no reconstruction is given. Eotriceratops is one example, but there are others. The worst offender I've ever read was Mapusaurus, a giant South American theropod known from several individuals of various growth stages. Almost the entire skeleton is known. But it's description, by Coria & Currie (2006) fail to provide even drawings of the individual bones, much less a reconstruction of the skeleton.

For me, if I can't draw it, I don't know what it looks like.

Anyway, if you want to read a good summary of the Eotriceratops paper, Brian's got you covered. He does well to point out the unusual bite marks on the base of one of the supraorbital horns. The paper itself, however, mentions the bite marks in passing, without speculating on how they got there or what made them. This is another failing of the description. Another disappointment is that you read the paper, which doesn't really consider the overall structure of the frill (except for an overly-long discussion on the unique epoccipitals), and then you look at the photos here and below, and suddenly the frill is solid (and huge).

According to the paper itself, the frill is largely unknown, so I'd be interested to hear their justification for not putting some fenestrae in there. In their phylogenetic analysis, Eotriceratops falls into one of two positions (both of which are equally parsimonious): Either it's a sister taxon to Triceratops, or an outgroup to Triceratops and (Diceratops + Torosaurus). Either way, you would expect to see some fenestrae in there, especially in the latter hypothesis.

Keep in mind that Triceratops, as Brain notes, is unique among horned dinosaurs in lacking windows in its frill. Aside from providing an interesting question as to where the animal's jaw muscles attached, the strange frill has actually obscured Triceratops' true affinities, as its frill is more like that of a centrosaurine. Anyway, since the closed frill is obviously a derived feature, one would expect that an ancestral Triceratops would have at least small fenestrae. And if Eotriceratops is ancestral to the entire "Triceratops group," then I would almost require it to have holes in the frill. No justification for a lack of holes is given, and that really annoys me.

Finally, somebody really needs to redescribe Diceratops. The Eotriceratops paper treats it as not just a separate, distinct genus, but also as a sister taxon to Torosaurus rather than Triceratops! The picture directly above, by the way, is a reconstructed Diceratops skull. Although I'm not entirely surprised that it was found as a sister taxon to Torosaurus (looks a lot like it ahead of the frill), to see it suddenly move from "possible synonym of Triceratops" to "sister taxon of Torosaurus" is a little strange*.
So I wasn't terribly impressed with the Eotriceratops paper, for the reasons set forth above. And we need more information on Diceratops. One last thing! Does anybody out there in readerland have Albertaceratops' paper? I would love to do a reconstruction of that critter, but I need its description first!
*To be fair, Diceratops shares Torosaurus' vertically-oriented supraorbital horns and low nasal horn, but the frill just screams Triceratops.


Mike said...

You should be pleased then that those wild and crazy guys at SV-POW! provided a 'reconstruction' of the whole of Xenoposeidon proneneukos from their one partial vertebra, showing where the specimen comes from and complete with a little human for scale. :-)

ReBecca said...

Check out Octavio Mateus's new paper in the Journal of Paleontology. He changes Diceratops to Dicerats.