Wednesday, April 22, 2009

Not Deinocheirus, but still pretty cool

Along with Xiongguanlong, another new theropod was announced today in Proceedings B: A giant ornithomimosaur!

(not Deinocheirus).

No, it's not the quasi-mythical giant-armed wonder, but it's still a pretty big ornithomime. Named Beishanlong grandis, is not only big, but fairly primitive as ornithomimes go. It's similar to Harpymimus, though without a skull, we can't tell whether or not it had teeth and to what extent. Clues from the post-cranial skeleton, however, place it in between Shenzhousaurus and Garudamimus. This is pretty interesting as it shows that ornithomimids evolved very large size at least three times (and depending on where Deinocheirus falls out, maybe four). Other large ornithomimes include Gallimimus bullatus from Mongolia, and Struthiomimus sedens from Canada. Beishanlong was larger than both of these, weighing in at 626 kg compared to 440 kg for Gallimimus. By my reckoning that makes it the largest ornithomimosaur known (except, of course, big D.).

Image here is from the FMNH press kit.

The Despot

Today is a biggie for dino fans: at least three new species were announced and several dino-related papers published. Since we all know theropods are the best and everybody loves T. rex, I'll cut right to the quick:

First up is a brand new tyrannosauroid from China, Xiongguanlong baimoensis. Tyrannosaurs are of course known as "tyrant lizards," but Jaime Headden has coined another term for basal, small tyrannosauroids that fall outside the family Tyrannosauridae proper: despots. Xiongguanlong (pronounced SH'ONG-gwan-long) is a despot on the verge of becoming a tyrant, unlike its sort-of-namesake, the much earlier and more primitive Guanlong. As you can see in the skeletal drawing here (from the Field Museum press kit), it also has a very narrow, almost spinosaurian skull (the authors describe it as "longirostrine", or long-snouted). This helps muddy up the presumed straight-line (ha!) evolution of tyrannosaur skulls from lightweight, boxy primitive forms to heavyweight, bone-crushing advanced forms (though at least one proper tyrant, Alioramus, also has a fairly narrow snout).

One fun thing to do when new dinosaurs get lots of media attention to the point people are sending out press kits (what, was Paul Sereno involved in this?) is to laugh at the silly "science" journalists employed by most newspapers and see just how much they misunderstood what the scientists told them. In all fairness, most media hype about new dinosaurs is just that, and the scientists are sometimes complicit in this. After all, what's exciting about a new find for scientists because it clears up some small details of evolution might be lost on the general public unless they see it as filling in some MAJOR gap (people love "missing links" even though there's no such thing, every species is a link to some other species).

Here's an example from the BBC News story on Xiongguanlong:
  • "Tyrannosaurus rex may have had much smaller ancestors"

No kidding? You mean it didn't evolve from even larger tyrannosaurs? Not to mention all the media hype two years ago over Guanlong, which was... a small ancestor of T. rex. Or Appalachiosaurus before that. Or Dilong before that. Eotyrannus before that. The caption aside, the text mainly puts this in the right context--it's not a new discovery that tyrannosaurs had small ancestors. What's significant is that it fills in a gap between the Late Jurassic and Early Cretaceous despots and the Late Cretaceous tyrants, hailing as it does from the middle of the Cretaceous Period. That's why, I guess, the story on ScienceNews dubbed it the "Goldilocks Tyrannosaur."

Anyway, I'm still working on getting this paper and reading more than just the abstract and Makovicky's comments in news articles, so I'll keep an eye on the threads to see if any more fun info on despots comes up.

Monday, April 6, 2009

What's In A Name? Brontosaurus Returns?

To elaborate on the previous story:
As you all probably know, the reason the name Brontosaurus was abandoned in the first place is that it turned out to be a subjective junior synonym of Apatosaurus. (NB: It was NOT because it was a chimera. The whole "wrong head" thing is a separate issue and overstated anyway. That head was a decent educated guess at the time!) Basically, Apato was named first, people decided they belonged to the same genus (note: not species), and so the name Brontosaurus was sunk since it was coined second.

[Image: Apatosaurus mount at the AMNH. According to he SV-POW goss mentioned previously, this will remain Apatosaurus even after Brontosaurus is resurrected. Photo by Erika & Shannon, from Wikipedia, some rights reserved.]

If you're really observant and know something about taxonomy, you can see why this was not an open and shut case or a definitely permanent change. First of all the synonymy was subjective, not objective. Apato and Bronto appeared to belong to the same genus, but were not named for the same exact specimen, so the synonymy was more of an opinion. Especially given that it was generic, not specific synonymy. When species get sunk, it tends to stick. Whether two species belong to the same genus, however, is entirely dependent on whether you're a lumper or a splitter. Tom Holtz coined the term "genericometer" for the mental device people use to demarcate genera, and to illustrate just how subjective it is. With a finely-tuned genericometer, every genus only has one species (often over-splitting taxa). Loosen the settings on yours, and suddenly Daspletosaurus torosus is looking a lot like it should get renamed Tyrannosaurus torosus (probably a case of over-lumping).

This whole business has been simplified somewhat by phylogenetic taxonomy. Broadly, when all taxa should also be clades, it's easy enough to split and lump based on relationships. Daspletosaurus is less closely related to Tyrannosaurus than a few other species, so if you lump one you must lump all (or else the taxon Tyrannosaurus would become polyphyletic, an unnatural grouping), which doesn't make much sense and is not very useful in communicating about dinosaurs.

[Image: Drawing of the Brontosaurus skeleton by O.C. Marsh, 1896. Public domain.]

On the other hand, Apatosaurus and Brontosaurus are each others closest relatives, so you're not leaving anything out by lumping them. It forms a natural group, so it makes sense.

Or do they form a natural group? When a new paper was published on Supersaurus in 2007, the authors pointed out that it shared many features with apatosaurs, and belonged to the clade Apatosaurinae. In an offhand way with little elaboration, they mentioned Supersaurus has some characters that link it to Apatosaurus louisae in particular. This is significant, since that's the non-Brontosaurus species. If Supersaurus is closer to A. louisae than to A. excelsus (aka Brontosaurus), that means Apatosaurus would not form a natural group unless Supersaurus was also sunk into Apatosaurus, which, like in the tyrannosaur example, makes little sense.

Word on the tubes is that this is exactly the case. Supersaurus is likely closer to Apatosaurus than either are to Brontosaurus, and that means Brontosaurus needs to be brought back as a valid name. Sources say exactly this is in the works now, and a new paper will show that Supersaurus does indeed split up the Apatosaurus band. Look for news media sources trumpeting the return of one of the most famous dino names ever in the next year or so.

Stay tuned for more Bronto- related news, Brontosaurus, and otherwise... (hint hint?).