Saturday, December 31, 2011

Happy New Year! The Database is updated!

Check it out!  All the 2011 taxa are there.  I'm off to party....

Surprise! Jeholornis palmapenis isn't valid.

What's that you say?  ANOTHER supposedly new Jehol basal avialan is just a junior synonym of a known species?!  Shock!  Gasp!  This time it's none other than the armless Jeholornis palmapenis (insert priapic joke here).  On the plus side, at least the description is better than others so far published, so this will help when coding Shenzhouraptor sinensis for matrices.

O'Connor et al. (2012) listed several characters supposedly distinguishing this taxon from Jeholornis prima.

The single preserved maxillary tooth and second empty alveolus contrast with IVPP V13274 (the prima holotype), V13550 and V13553 (both referred to prima), which have been reported to lack maxillary teeth. Yet jeholornithid teeth are often unpreserved due to their small size and low number, as seen by palmapenis' lack of dentary teeth (considered preservational by O'Connor et al.) and LPM 0193's (the Shenzhouraptor holotype) lack of any recognizable teeth. Even palmapenis only preserves one of the at least two maxillary teeth it had on that side. Thus the absence of maxillary teeth in other specimens may easily be preservational.

The presence of two pairs of anterior dorsal pleurocoels was listed as diagnostic (grading into a single pair posteriorly), but pleurocoel number often varies between different vertebrae and even sides of the same vertebra in theropods. Anterior pleurocoel number has not been described in any other jeholornithid specimen, but IVPP V13353 shows single pairs in dorsals nine and eleven, and three pairs in ten. Until palmapenis is shown to be consistantly unique in pleurocoel number, this character is not considered diagnostic.

Comparison of palmapenis ilium (top; after O'Connor et al., 2012) with prima (bottom; after Zhou and Zhang, 2003).  Note the ventral edge of the postacetabular process (blue) is not significantly more concave in palmapenis.  Note also the obvious breakage of the ilium (circled in red), making the dorsal border look highly convex.  The upper right picture shows superimposed and flipped images of the anterior left ilium and posterior right ilium to show the dorsal margin (surrounded by green) is straight.  Note that when the dorsal margins are lined up this way, the preserved posteroventral portion conveniently follows the outline of the other pubic peduncle.

The ilium is supposedly strongly convex dorsally, but it's clear the anterodorsal portion has merely been broken off, with no dorsal margin remaining anterior to the acetabular midpoint. The margin posterior to this is slightly convex as in other jeholornithid specimens. The anterior dorsal margin is preserved on the disarticulated left ilium, which forms a similar overall ilial dorsal convexity to other jeholornithids when rotated into place. Similarly, though the postacetabular process was described as strongly concave ventrally, the concavity is almost identical to that in IVPP V13353 (20% distance from line stretching from top of acetabulum to ventral postacetabular tip is 20% of ilial depth above acetabulum, compared to 19%) and other jeholornithids (the supposedly straight margin of IVPP V13274 looks slightly curved in the photo, and any difference would be insignificant in any case).

The dorsally curved ischium was also said to be diagnostic, but the distal ischium is unpreserved in the prima holotype, with the reconstructed portion being part of the tibia or fibula instead. Indeed, O'Connor et al. state ischial curvature is unclear in other Jeholornis specimens. LPM 0193 shows a dorsally curved ischium, albeit less so than in palmapenis.

In the tail, the transition point was stated to be more gradual (in central elongation) and posterior (at caudal seven instead of six) in palmapenis than IVPP V13550. Yet the transition point is also different in IVPP V13353, where the first elongated caudal is five, and IVPP V13274, where it seems to be at four (an unlabeled caudal is disarticulated adjacent to the last sacral). Differences in transition point abruptness are present as individual variation in other taxa, such as two nearly identical Microraptor specimens (CAGS 20-7-004 and 20-8-001), where the difference between lengths of caudals three and four is 9% in one and 53% in the other). Both caudal differences are thus more probably individual variation.

Finally, the diagnosis lists "elongated caudals possess chevrons with hooked articulations", but these articulations are not mentioned again and photos show normal, straight dorsal, anterior and posterior ends as in other paravians.

Of the diagnostic characters listed for prima by O'Connor et al., the ones not mentioned above are all unknown in palmapenis (except the robust dentary, which is true for all jeholornithids). In the text, the dentaries are said to appear unfused unlike the prima holotype, but they note this may be due to poor preservation. It may also be due to ontogeny, as palmapenis is smaller and has an unfused metatarsus. The text also states the ilium differs in having a bround rounded preacetabular process supposedly unlike IVPP V13274, but this is due to the latter being in medial view and not showing the ventral flange that would be lateral to the cuppedicus fossa, as seen in IVPP V13353 and LPM 0193.

So of the listed differences from prima, only the difference in maxillary dentulousness can even be plausibly considered true and not subject to individual variation. Ironically there are some valid differences not mentioned in the text. The dentary is a third deeper than the prima holotype and IVPP V13350, which is opposite the expected trend for a juvenile. The ischium slightly expands at its tip, unlike the Shenzhouraptor holotype. But since the first difference is not observable in the Shenzhouraptor type (whose anterior dentary angles beneath the skull) and the second difference is not observable in the prima type (whose distal ischium is broken off), these would form a weak differentiation from either species. As both character states are derived in Avialae, Shenzhouraptor and prima could not be united by their counterpart states. Instead, until they are shown to have a consistant variation between multiple specimens, the differences are more readily ascribed to individual variation as is found in any theropod known from large sample sizes (Allosaurus, Tyrannosaurus, Microraptor, Archaeopteryx). Jeholornis palmapenis is here made a junior synonym of Shenzhouraptor sinensis.

Referennces- Zhou and Zhang, 2003. Jeholornis compared to Archaeopteryx, with a new understanding of the earliest avian evolution. Naturwissenschaften. 90, 220-225.
O'Connor, Sun, Xu, Wang and Zhou, 2012. A new species of Jeholornis with complete caudal integument. Historical Biology. DOI: 10.1080/08912963.2011.552720

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.

Friday, December 2, 2011

Top 10 Most Poorly Described and Illustrated Mesozoic Theropods

Look at that, I managed to skip a month between posts.  The hazards of coding, illness and other such excuses.  Here's a quickie that was fueled by my annoyance at any significant primary literature while coding Adasaurus.  These are the theropods whose publically available information is the most paltry compared to the completeness of their remains, and have been officially described already in the literature.  The relative importance of the taxon isn't a factor, and taxa whose remains are lost aren't considered due to the impossibility of their redescription.

10. Anserimimus
Anserimimus' holotype is a skeleton missing only some cervicals and the skull, but only the scapulocoracoid, manus and metatarsus were described and illustrated by Barsbold (1988).  Kobayashi and Barsbold (2006) helped a bit, as does Bronowicz's (2011) fragmentary but well described specimens.  But what keeps this from scoring higher is the availability of good photos of the mount (e.g. this) and Kobayashi's (2004) coding it for several matrices.

9. Tie between Cristatusaurus, Deltadromeus and Afrovenator
These taxa all have a common theme- Sereno described them (well, he described Suchomimus, which I sink into Cristatusaurus).  Published by the king of the Science tabloid, featuring a Paulian skeletal and several zoomed in line drawings, these taxa have yet to be redescribed in detail.  While there are photos of mounted skeletons available, these are all casts.  The best source of information on these are the matrices of Rauhut (2003) and Benson (2010).

8. Aucasaurus
Basically complete, but only the proximal tail, arm and lower hindlimbs have been illustrated and briefly described.  Recently, the braincase was also described, though I lack that paper so far.  Ceratosaur matrices like Carrano and Sampson (2007) have some info.

7. Inosaurus
Known from quite fragmentary remains, but very poorly described and only illustrated by two partial vertebrae (apparently my tracing survives unattributed online).  Is it even dinosaurian?

6. "Chilantaisaurus" zheziangensis
Dong (1979) gave this proximal tibia and partial pes a fairly useless description and illustrated two pedal digits in ventrolateral view and curving towards the viewer. :|  Therizinosaurian affinities have been suggested, but it's not been examined since.

5. Kaijiangosaurus
Only a few vertebrae, pectoral girdle and proximal/distal metatarsal outlines have been illustrated, and the description has yet to be translated from Chinese.  An online photo shows a lot more is known, but also that size differences mean more than one individual/taxon are present.

4. Conchoraptor
Ah, Conchoraptor.  You might be asking how can this be obscure when there are so many skeletons casted.  I've even seen two in person.  The problem with Conchoraptor is that it's unsure just which specimens belong to it, besides the holotype (of which we have illustrations of the skull, and a manus and metatarsus that presumably belong to it or a paratype).  None of the articulated skeletons photographed online have the right manual proportions or slender metatarsal II, and crestless skulls like ZPAL MgD-I/95 (the one described by Osmolska, 1976 and which Kundrat has recently been describing braincase details of) and the one on Witmer's lab page identified as "Ingenia" could belong to other oviraptorids.  No one has ever provided a modern diagnosis, described the holotype in any detail or justified the referral of other specimens.  This makes depending on matrices more risky than for other taxa listed here, since their OTU could be chimaerical for all I know.

3. Rinchenia 
This has been illustrated in the literature even more seldomly than Conchoraptor, since at least ZPAL MgD-I/95 has papers dedicated to it.  We only have the skull, mandible, overly schematic ilium and a single caudal vertebra illustrated.  Lucky for us, Auditore was able to obtain photos of the holotype and illustrate it as detailed by Cau on his blog.  As for Conchoraptor, Norell et al. (2001), Lu (2004) and Maryanska et al. (2002) all provide codings, which can be trusted more for Rinchenia since there's only the holotype (though I note a recent incorrect trend of referring IGM 100/42 to it).

2. Adasaurus
The muse for this post only gets second place.  For Adasaurus we must depend on a few schematic drawings (pelvis, metatarsus, pedal digit II), since Barsbold (1988) neither described it besides noting a couple features, nor does he allow photos to be circulated.  There was a photo of the holotype online which has since disappeared, but shows Barsbold's pelvis illustration is inaccurate, and to make it worse Kubota (pers. comm. to Senter, 2010) indicates the supposed small sickle claw doesn't belong.  I'm just hoping Kubota plans to redescribe the taxon like Kobayashi did for Barsbold's basal ornithomimosaurs.  Until then, we depend on codings from Norell et al. (2001), Senter (2007) and Longrich and Currie (2009), and a few scattered notes.  Hopefully Turner et al.'s upcoming dromaeosaurid monograph has some juicy photos.

1. Chilantaisaurus? sibiricus
There are a lot of fragmentary taxa known from a tooth or a vertebra that are poorly described (usually in a useless archaic way) and illustrated in a photo from a single view.  What makes sibiricus stand out is that Riabinin (1914) didn't even identify which element the holotype was, let alone try to describe its features.  He just said it was hollow and belonged to the limb of a fairly large theropod, probably a megalosaurid (named as Allosaurus? sibiricus).  Even worse, he didn't illustrate it, only [Edit: Chure 2000 and Benson and Xu 2008 were incorrect about the lack of illustration and brevity of description; I've since examined the taxon here] providing six measurements (proximal width 48 mm, proximal depth 39 mm, distal width 68 mm, distal depth 62 mm, cavity width 22 mm, cavity depth 17 mm).  Huene (1932) identified it as a distal metatarsal IV without rationale, but said only that it did not permit exact characterization and probably belonged to an allosaurid (renamed Antrodemus? sibiricus).  Molnar et al. (1990) then said it was "almost identical with that of C. tashuikouensis in form and proportions of the distal condyle", so questionably referred it to that genus.  You now possess the entirity of published information on sibiricus.  Makes the available information on Adasaurus seem like an overflowing feast.