Wednesday, December 28, 2011

Dino Discoveries of 2011!

With the new year rapidly approaching, I will now take the time to reflect on what dinosaur discoveries were made during the year of 2011. The previous year, 2010, featured a plethora of new ceratopsian discoveries, including Utahceratops gettyi, Kosmoceratops richardsoni, and Vagaceratops irvinensis. Well, if 2010 was the Year of the Ceratopsian, then 2011 is the Year of the Troodontid! 3 new troodontids were discovered, this year: Xiaotingia zhengi, Linhevenator tani, and Talos sampsoni. This is more troodontid species disovered during a single year than in any other year in history, so far, ever since Troodon formosus was first described and named by Joseph Leidy, in 1856. Now, obviously, for Troodontid fans, like me, 2011 was a really awesome year!

Besides troodontids, several other dinosaurs have been discovered this year, including tyrannosaurids. Two tyrannosaurids have been found, this year: Teratophoneus curriei, and Zhuchengtyrannus magnus. Teratophoneus is significant, because it is one of the very few relatively well-preserved tyrannosaurids known from southern North America. It was described by Carr, Williamson, Britt, and Stadtman. It is classified in the tyrannosaur subfamily Tyrannosaurinae, which also includes the (in)famous Tyrannosaurus rex. It differs from other tyrannosaurids, in that it had a very short and deep skull, indicating that it presumably had a relatively strong bite force. Zhuchengtyrannus, on the other hand, was discovered in China. It is very closely related to Tarbosaruus bataar, sharing numerous features with it, especially in the skull and teeth. It was a very large predator, reaching lengths of up to 37 feet in length, and weights of up to 6 tons.

In addition to these, a new primitive theropod from the Triassic period has been discovered in South America. Its name is Eodromaeus murphi. It is believed to be one of the earliest known theropod dinosaurs, ever to have lived. It was described in 2011 by paleontologists Ricardo N. Martinez, and Jim Murphy.

Another newly-described dinosaur is Haya griva, an ornithopod, which was discovered in Mongolia. Several specimens were recovered, from 2002, to 2007. Haya is unique, in that one of the specimens preserves an enormous amount of smooth gastroliths, or "stomach stones", inside its rib cage. Although we are not yet completely sure, it is certainly possible that the animal had swallowed these stones, in order to aid it, in digestion.

And, finally, I am now going to talk about the troodontids. As I stated previously, three new troodontids have been discovered, in 2011. One of these is Xiaotingia. It was discovered in China, and described by Xu Xing and colleagues, in July 2011. Xiaotingia is very similar to Anchiornis huxleyi, another troodontid, discovered in 2009. Indeed, a cladistic analysis proved that it was actually the sister species of Anchiornis. However, perhaps what this dinosaur is most famous for is the controversy surrounding it. You see, in Xu's paper, he originally described Xiaotingia as being an archaeopterygid, rather than a troodontid. He then moved Anchiornis into the Archaeopterygidae, as well. He also re-classified the Archaeopterygidae as being deinonychosaurs, rather than primitive birds. This re-classification was very popular, in the media, with several articles online running headlines saying, "Archaeopteryx is no longer a bird!" and "Bird no longer: A prehistoric icon is knocked from its perch".

However, in early November 2011, another article by Lee and Worthy came out. Using the maximum likelihood phylogenetic assessment, they were able to figure out that Archaeopterygidae does, indeed, actually belong in the Avialiae, and not in the Deinonychosauria. In addition, the family was revised to include only Archaeopteryx and its close relative, Wellnhoferia. Thus, both Anchiornis and Xiaotingia were then taken back into the Troodontidae.

Xiaotingia was a very small troodontid, only about the size of a crow, or a raven. It preserves evidence of feathers on its body, just like numerous other small, feathered dinosaurs discovered in China.

The next troodontid is Linhevenator, which was officially described and named by Xing Xu and colleagues, in September 2011. Its remains were recovered from the Bayan Mandahu Formation, in Inner Mongolia, China. Linhevenator is unique, for several reasons. First of all, it is relatively rather large, for a troodontid, being slightly longer than the type specimen of Saurornithoides mongoliensis. Second of all, it displays a mixture of plesiomorphic and derived characteristics, which makes its exact phylogenetic placement somewhat difficult, to determine. However, the study managed to show that it was a more derived troodontid, in a polytomy formed by Troodon, and a clade containing Saurornithoides and Zanabazar.
Linhevenator also had large, dromaeosaurid-like sickle-claws, on its feet. These were much larger than those of more primitive troodontids, such as Sinovenator and Jinfengopteryx, indicating that derived troodontids converged with dromaeosaurids, in that they both developed rather large sickle-claws, on their back feet.

However, perhaps the most fascinating feature of Linhevenator was how it had very short arms. The arms of Linhevenator were very short, comparable in length to those of Austroraptor, or Compsognathus. It is currently unknown how, exactly, Linhevenator used its arms, although they might possibly have been used for digging, climbing, or help in mating displays.

The third troodontid described in 2011 is Talos, which was named and published by Lindsay Zanno and colleagues, just a couple of weeks after Linhevenator. It was very unique, for several reasons. First of all, it was discovered in the Kaiparowits Formation in Southern Utah. This makes it the very first troodontid besides Troodon that is known to have lived in North America, during the Late Cretaceous time period. This has very important implications, as the authors of the study noted, because it shows that the numerous remains assigned to Troodon are probably "overlumped", and that several species of Troodon, besides T. formosus, likely lived, in North America.

However, the most incredible characteristic of Talos is its great pathological value. The second toe on its foot, (the one bearing the deadly sickle-claw), was injured. Although we currently have no idea exactly what caused this injury, it must have been sustained either during prey capture, or in fights, with another member of the species.

Overall, 2011 was an awesome year, for dinosaurs! And, perhaps the most awesome thing about it, in my opinion, is how so many troodontids were discovered, during this past year. According to the Chinese Zodiac calendar, 2011 is officially the Year of the Rabbit. However, in my book, it is the Year of the Troodontid! Hmm…I wonder what 2012 is going to be? The Year of the Dromaeosaur? The Year of the Ornithopod? The Year of the Titanosaur? The Year of the Stegosaur? Well, I guess we will just have to wait and see!