Monday, December 26, 2011

Merry Christmas! It's Xu's Thesis

I received a wonderful Christmas present this year- a copy of Xu's (2002) thesis on Liaoning deinonychosaurs which I've wanted for a decade now.  It's referenced in most of Xu's publications, but not in many others, and since it's not available in pdf, the info is difficult to come by.  This is one of the best publications on theropods I've read, so I'll sum up the contents here.

The first section is an osteology of the holotype of Sinornithosaurus.  The cranial and pedal sections have been published (as Xu and Wu, 2001 and Xu and Wang, 2000), but the axial description was most interesting to me.  It preserves 21 presacral vertebrae and the first nine caudals, yet these are not easily identified in the original tabloid description, unlike the pectoral girdle, manus and pelvis, which show most of their characters in the original figures.

The second section is an osteology of Microraptor's holotype, but also a specimen otherwise unmentioned in the literature- incomplete skeleton IVPP V13475 from the Jiufotang Formation, missing only some caudal vertebrae and the left manus.  This provides us with the Microraptor skull description I've been waiting for, and is what the reconstruction in Xu et al.'s (2011) paper is from, and what many of the codings for Microraptor in Xu and Zhang's (2005) matrix are from.  The rest of the description is less useful now that we have Hwang et al.'s (2002), but does feature interesting details like a large coracoid fenestra as in Sinornithosaurus and a straight pubis unlike other microraptorians.

The third section is an osteology of the then-undescribed Graciliraptor, so "Graciliraptor lujiatunensis" Xu, 2002 is a nomen nudum used prior to 2004. The description is better than the published version, but not by much since it was published in a real journal, and the specimen is fragmentary to begin with.

The fourth section is my favorite- a detailed osteology of the holotype and paratype of Sinovenator.  The species name is given as changae, as opposed to changii, since Li noted it was grammatically incorrect.  Creisler noted this on the DML that year too, but suggested changiae. Since it's named after a woman named Chang, I think changae would be right, but as I note on the Database, the Fourth Edition of the ICZN no longer requires emendations based on this reasoning (Article 31.1.3).  Nomenclature aside, the description is excellent and includes such needed things as an anterolateral view of the coracoid, posterior view of the braincase, and multiple views of presacral vertebrae.  Since we really don't have any detailed published descriptions of basal troodontid anatomy, and Sinovenator is basically complete (missing most of the palate, the quadratojugal, part of the mandible, half the cervicals, the post-26 caudals, ribs, and part of the hand), this section is vital to anyone studying paravian phylogeny.

The next section is about the feathers of Liaoning dromaeosaurids, which I normally would find boring, except that among the specimens described and photographed are Microraptor gui paratypes IVPP V13477 and V13320.  Of course, M. gui was a year away in 2002, so Xu refers to them as Sinornithosaurus sp. and Microraptor sp. respectively.  Interestingly, IVPP V13320 has completely serrationless teeth, while most Microraptor specimens have only distally serrated (posterior) teeth, and NGMC 00-12-A has posterior dentary teeth with serrations on both carinae.

The last section is one I would normally be very excited about- the phylogenetic analysis.  But it's basically the same as Xu and Zhang's (2005) with one less character and without Scansoriopteryx, Shenzhouraptor and Pedopenna (careful readers will note two mentions of Shenzhouraptor as an unnamed new bird without a pygostyle and one mention of Zuolong as an unnamed basal coelurosaur).  Xu runs lots of variations (cranial only, postcranial only, only basal taxa, only derived taxa, excluding various taxa) that would have been very interesting back in 2003, but since so many new taxa are lacking, are now more of historical interest like my Evaluating Phylogenetic Analyses section.  One good thing is that he describes several of the characters in depth and even provides graphs showing ratio distributions, so that they can be evaluated better than most TWG characters.

Xu ends with extensive measurement tables for the specimens described in the osteologies, but unfortunately not for the M. gui paratypes.  I would have liked more illustrations, but Xu's descriptions are top notch, and are badly needed for taxa described in tabloids like Sinornithosaurus and Sinovenator.  I don't know why most of this material was never published, since it's been written up for almost a decade now.  Similarly, I can only hope something of this caliber is written up for Beipiaosaurus and Mei.  Unfortunately, I only have a hard copy, so cannot send pdfs yet.

References- Xu and Wang, 2000. Troodontid-like pes in the dromaeosaurid Sinornithosaurus. Paleont. Soc. Korea Special Publication. 4, 179-188.
Xu and Wu, 2001. Cranial morphology of Sinornithosaurus millenii Xu et al. 1999 (Dinosauria: Theropoda: Dromaeosauridae) from the Yixian Formation of Liaoning, China. Canadian Journal of Earth Sciences. 38, 1739-1752.
Hwang, Norell, Qiang and Keqin, 2002. New specimens of Microraptor zhaoianus (Theropoda: Dromaeosauridae) from northeastern China. American Museum Novitates. 3381, 1-44. 
Xu, 2002. Deinonychosaurian fossils from the Jehol Group of Western Liaoning and the coelurosaurian evolution.  PhD Thesis. Chinese Academy of Sciences. 325 pp.
Xu and Zhang, 2005. A new maniraptoran dinosaur from China with long feathers on the metatarsus. Naturwissenschaften. 92, 173-177.
Xu, You, Du and Han, 2011. An Archaeopteryx-like theropod from China and the origin of Avialae. Nature. 475, 465-470.

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