Tuesday, June 30, 2009

How Mimsy Was Zanabazar?

No, not the early Mongolian Buddhist leader.

Above: Not a troodontid.

Zanabazar is the newly-coined name for the troodontid previously known as Saurornithoides junior. A new review of the genus Saurornithoides by a heap of authors including Mark Norell and Rinchen Barsbold himself (who named S. junior in 1974) found that the evidence linking S. junior to S. mongoliensis as each others closest relatives is lacking, so a new genus name was needed for junior (I would have gone with "Henryjonesius" in honour of Sean Connery).
Above: Zanabazar junior by FunkMonk, licensed.

But wait a second... there's been talk for some time now that S. junior may be synonymous with another small troodont, a contemporary from the Nemegt Formation with one of my personal favourite dino-bird names, Borogovia (after one of the nonsense creatures in Lewis Caroll's poem Jabberwocky.) I haven't read the paper yet so I'm not sure if this issue was addressed, but as it stands now, there still is no overlapping material to directly compare the two troodonts, so it's impossible to prove synonymy at the moment (Borogovia is known from leg and foot bones lacking the rest of the skeleton, Zanabazar is known from a partial skeleton lacking leg and foot bones). But if any further material for either species turns up, and they turn out to be synonyms, Borogovia will win the day as the older name. Not that Zanabazar isn't a cool name in and of itself. But how boss would it be to name a hypothetical new Nemegt therizinosaur (with their long necks, giant claws, and overall freakish appearance) after the Jabberwock itself? A mammal called "Momerathobataar"? "Tovia slithius" the nematode to complete the set? Will, 70 years later, an oviraptorid have to be re-named "Toviamaia"? Too many Nemegt fauna inside jokes? Yeah, I'll stop.

Above: The resemblance is uncanny! Left: Jabberwock by John Tenniel, 1871. Right: Therizinosaurus by Apokryltaros, licensed.

Nom nom nom

Above: Edmontosaurus skull, note teeth in back of jaw. Photo: Ballista / Wikipedia, licensed

Did hadrosaurs chew? A recently named lambeosaur called Angulomastacator ("angle chewer") would have us think so. So would a new paper by Williams et al. on an intensive study of hadrosaur tooth wear. As this article reports, the direction of hundreds of scratches were mapped in 3D to suss out what type of chewing method was used by hadrosaurs. The authors found that they employed an extinct form of chewing unlike any living animals, in which the natural kinesis (joints between the skull bones found in modern reptiles) forced the bones of the upper jaw outward, causing the tooth batteries to slide against each other in a sideways motion.

Sounds very interesting and a great step to resolving the ecologies of this well-known dinosaur group... or is it? A major paper that came out in the December issue of JVP argued convincingly that dinosaur skulls such as this didn't actually have any kinesis at all! As David Marjanovic summed up on the DML, the argument there was that people who have spent their careers studying modern reptiles and their kinetic skulls have assumed that dinosaurs followed the same pattern, and have grasped at straws to find evidence of kinesis where it doesn't actually exist (that is, that dinosaurs lost cranial kinesis at some point in their evolution from other reptiles, or never had it, meaning it's a novel feature of lizards and snakes). If that's the case, than the underlying assumption of this new hadrosaur paper is wrong. Another blow against their conclusions, as noted in the article above, is that reports of fossil stomach contents from hadrosaur mummies show food that had been sheared, not chewed. Gut contents also suggest a diet predominantly of conifers (pine trees etc.), while the tooth wear study suggests food was cropped close to the ground and may have been rich in silica, suggesting a diet primarily of ferns and horsetails.

Above: Edmontosaurus tooth battery, which was studied for wear patterns. Photo: Vince Williams / Univ. of Leicester

So then, how to explain the unique wear patterns on hadrosaur teeth? How can we rectify the conflicting evidence regarding diet? Surely another salvo in this controversy will appear in print in a few months.

Friday, June 5, 2009

Tracy Ford and the Kingdom of the Embellished Skull

It's a catch-phrase for Indiana Jones and a rallying cry for paleontologists and archaeologists alike...

"It belongs in a museum!"

Unfortunately, there are plenty of private collectors out there who don't heed Indy's sage-like advice. Many important fossils are lost every year to private individuals who rarely disclose specimens to experts for study. Even if specimens in private hands are offered to experts, many refuse to publish on them, partly because they see it as simply unethical and partly because most important provenance data (what rocks formation the bones came from, etc.) has already been lost by that point.

Take the case of the Mongolian tyrannosaurid Alioramus. This dinosaur is officially known from only a single decently preserved skull, though several more complete skulls are known to exist in private collections, making them all but worthless to science unless the collectors bequeath them to museums in their wills later on. Mongolia is notorious for losing specimens to collectors, and apparently many, many excellent, potentially very important finds and new species will never become known to the public for this reason.

Back to Alioramus. One such 'lost' skull was recently sold at auction in New York to an undisclosed buyer for over US$200,000 (story here). Photos of this specimen were posted to the Dinosaur Mailing List after the auction finished (see DML post here for links to all the photos. One is reproduced above).

This seems like a tragic sale, because the skull appears to be beautifully complete, so it would be quite a loss for it to end up under a glass case in some millionaire's bedroom. I say would, because it looks like the joke's on him or her...

Often ignored in the sale of private specimens inaccessible to science is that they're inaccessible to science. That means that embellishments often added to black market fossils can't be caught by trained eyes. Now, at first glance, even most experts wouldn't notice the enhancements to the skull pictured above without studying the fossil up close. Enter Tracy Ford: the original armchair paleontologist, he has made a name for himself in offering a subscription-based online dinosaur database, as well as producing numerous publications on dinosaur life anatomy, books on how to draw dinosaurs, etc. Ford is also an active member of DinoForum, and noticed something very familiar about the auctioned-off Alioramus skull. He'd seen it before, at the infamous Tuscon Gem and Mineral Show. Tuscon is a Mecca for fossil collectors and under-the-table deals on shady specimens. The show regularly attracts even pros, who can often come across amazing new finds.

Ford had seen this very skull at the show, and, as he reported on DinoForum:
  • "I can saw with total confindance that this specimen is more than 80 percent reconstructed. The reason why I know this is that it was at the Tucson Rock Show about 3 or 4 years ago and I took several photo's of the specmen, which at the time was just the premaxilla, maxilla and tip of the dentary. Nether of the bones complete. So, just to get it sold they reconstructed it into its current state. Not as good as they claim it to be."
Others were astounded that someone would pay over 200 grand for a specimen that hadn't been checked for reconstruction or forgery. "Completing" partial skulls is common even in museums when prepping specimens for display, but you'd reckon this would significantly decrease the value of a specimen at auction, and I'd be very surprised if the buyer knew that only the ends of the jaws were composed of real bone. Here's a photo Ford took of the specimen years ago in Tuscon. Worth $200,000? You be the judge.

Thursday, June 4, 2009

Empire of the Shark Teeth

Today saw the publication online of a paper finally re-describing Chilantaisaurus maortuensis, a theropod from mid-Cretaceous China. This species was assigned to the genus Chilantaisaurus in 1964 by Hu, and has been all over the map since then. Authors have variously considered it a tyrannosaur, an allosaur (linking allosaurs and tyrannosaurs, actually), and even a maniraptoran coelurosaur. While the exact identity of Chilantaisaurus proper remains a bit uncertain (latest word is that it may be a spinosaur), the new paper is pretty sure of its conclusion: C. maortuensis isn't Chilantaisaurus at all, but the first known Asian carcharodontosaur!

As the story goes (and as Steve Brusatte reported in a guest post at Archosaur Musings), during some down time in Beijing, and while working on his PhD thesis on tyrannosaurs, he got wind of this possibly tyrannosaurian specimen at a Beijing museum. It was immediately apparent to his eye that this was not a tyrannosaur, but a carch, which he and his colleagues finally renamed as Shaochilong maortuensis.

Not only is this the first Asian carch, but it fills a glaring hole in the Asian fossil record. Basal tetanurans dominated the large carnivore roles of Asia in the Jurassic, and tyrannosaurs like Tarbosaurus and Alioramus dominated in the Late Cretaceous. But what was going on in the mean time? Apparently, carcharodontosaurs, which were previously only known from the Americas, Europe, and Africa. This means that tyrannosaurs didn't arrive on the scene until the very end of the Cretaceous, much later than previously thought. Part of this has to do with the dating of the Ulansuhai Formation where Shaochilong was found. Previously thought to be Aptian-Albian in age, dating of underlying rocks shows that it must be at least Turonian (92 Ma), pushing the arrival of tyrannosaurs well into the Late Cretaceous.

So, did tyrannosaurs arise in Asia, migrate to North America, then migrate back to dominate Asia in the LK? We'll need more fossils to know the whole story. Given the Cretaceous age of
Shaochilong, we can't be sure whether carcharodontosaurs originated in Asia or migrated there from Europe, Africa, or North America, all of which have earlier carch species. But, as a special bonus as Steve points out on the blog linked above, this presents the first evidence that carcharodontosaurs could have battled ceratopsoids (in the form of Turanoceratops), horning in (haha, get it?) even further on traditional tyrannosaur territory.

Speaking of Asian tyrannosaurs, have you heard about that gorgeous complete
Alioramus skull recently auctioned off to a private collector and thus lost to science for probably ever? Well don't cry too much over it. More to come...

[Image: Chilantaisaurus from here.]