Thursday, September 30, 2010

Kayentavenator is not a tetanurine

Only five posts this month?!  Time to end September with a Kayentavenator series.

You may remember Kayentavenator from the discussions it ignited on the DML over whether Gay published it validly under ICZN rules.  I think the name is nomenclaturally valid, but that's not what I want to write about today.  The author rightly complained that the ICZN debate had completely overshadowed any attempt to discuss the paper's contents.  The only discussion so far has been that of Cau, who noted some anatomical identification issues and found it to be a basal theropod in his Megamatrix.  Unfortunately for Gay, the paper's contents hold up to scrutiny worse than the naming issue does.

Supposed tetanurine characters

UCMP V128659 was discovered in 1982 and referred to Syntarsus kayentakatae by Rowe (1989), as a subadult gracile individual. Tykoski (1998) did not examine it for his redescription of the species, but later (2005) examined it for his PhD thesis and considered it to be "probably referrable to "Syntarsus" kayentakatae" without discussion. Gay (2010) described the specimen as the new taxon Kayentavenator elysiae. Based on a small phylogenetic analysis, Gay placed Kayentavenator in Tetanurae but outside Avetheropoda. This was based on several characters which are all flawed.

The pubic articulation of the ilium is also larger than the ischial articulation in kayentakatae, and by a larger amount than Kayentavenator. The pubic peduncle's distal surface is also longer than wide in ceratosaurs and coelophysids like Megapnosaurus. The cnemial process arises from the lateral surface of the tibia in almost all theropods including kayentakatae. The trochanteric shelf is absent in all gracile and juvenile ceratosaurs and coelophysids, so cannot be used to place the juvenile Kayentavenator holotype in Tetanurae. Finally, the anterodistal femoral fossa is said to be non-elliptical in shape, which refers to a character originally used by Perez-Moreno et al. (1993). Ironically, in Perez-Moreno et al.'s analysis, the avetheropods were coded as having an elliptical fossa unlike Gay's analysis. In truth, avetheropods do not have fossae that are more or less oval than that of more basal theropods. While the fossa is poorly developed in Coelophysis, it is illustrated by Rowe in kayentakatae (as being non-elliptical due to its flat medial edge, for what it's worth) and is stated to be distinct in Segisaurus as well.

Gay also lists a feature in the description that is supposedly diagnostic of tetanurines- a pronounced sheet of bone projecting from the medial surface of the tibia, referring to Naish's (1999) description of BMNH R9385. Yet this must be a mistake as the feature Naish describes is the fibular crest on the lateral surface. However, Segisaurus has a prominent fibular crest comparable to tetanurines', while kayantakatae's is also described as large. There are therefore no characters placing Kayentavenator in Tetanurae.

Supposed differences from coelophysids

Gay states Kayentavenator "lacks a crista tibiofibularis and its associated groove, which are present in all coelophysoids and Dilophosaurus." Yet coelophysoids do not have a tibiofibular crest, the structure labeled as such by Rowe in kayantakatae being the ectocondylar tuber present in almost all theropods. Gay's description of Kayentavenator's femoral condyles is confusing as the "accessory condyle" is said to project from the medial condyle, yet the only accessory condyle in theropods including birds (which Gay states the accessory condyle of Kayentavenator resembles) is the ectocondylar tuber which is associated with the lateral condyle. Unfortunately, this supposedly unique morphology is not illustrated, with the femur only photographed in anterior view. Since the distal femur is separated from the proximal end in at least one element (and presumably the other, as the total length of both is said to be difficult to determine), it seems at least possible Gay confused the right and left distal femora. This would give them standard theropod ectocondylar tubers instead of apomorphically lacking the tuber and having a unique medial accessory condyle. In any case, young kayentakatae and Dilophosaurus specimens lack the deep groove lateral to the ectocondylar tuber, so its absence in the juvenile Kayentavenator specimen (confirmed by Tykoski, 2005) is expected.  

Kayentavenator is coded differently than "Coelophysisidae" [sic] in Gay's matrix for several additional characters. The caudal vertebrae are coded as having pleurocoels in the neural arch, which is not possible since pleurocoels are by definition a feature of vertebral centra. Furthermore, Gay states the position of the two partial preserved neural arches is impossible to ascertain. The pneumatic fossae are stated to face anteriorly on each side of the neural arch, indicating they may be anterior peduncular fossae as in Coelophysis cervicals, or even anterior infradiapophyseal fossae which all theropod presacrals possess. Since the neural arches are so fragmentary they cannot even be placed in the vertebral column (they are assumed by Gay to be from the posterior region only because the other remains are from the pelvis and hindlimb), they could even be backwards and merely exhibit posterior peduncular fossae as in all coelophysid cervicals including those of kayentakatae. Again, this supposedly unique feature is not illustrated, making evaluation difficult.

The brevis fossa is coded as being deep unlike coelophysoids, but coelophysoids including Megapnosaurus have deep brevis fossae. Coelophysids are oddly coded as lacking a supracetabular crest, which is untrue. They are also incorrectly coded as having an acetabular height only a third or less of the acetabular length, which is not true of any theropod (e.g. the ratio in kayentakatae is 88%). For the character "Pubic peduncle of ilium depth: 0, extends ventrally to the same level as ischiadic peduncle; 1, extends more ventrally than ischiadic peduncle.", coelophysids are coded as having nonexistant state 2 unlike Kayentavenator's state 0. In actuality coelophysids including kayentakatae have pubic peduncles extending ventral to their ischial peduncle. This is also true in Kayentavenator based on the stereophotograph in Tykoski's (2005) thesis, which does not agree with Gay's drawing. The photo also shows a complete articular surface on the pubic peduncle, while no obvious anteroventral corner to the process exists in Gay's illustration. Perhaps the peduncle was broken off during Gay's examination?

The obturator foramen is coded as open in Kayentavenator, despite Gay illustrating the ventral edge as closed but broken and stating the ventral margin was missing. Oddly, Kayentavenator is coded as having a pubic fenestra while coelophysids are not, despite the fact the latter are the theropods best known for having pubic fenestrae. Gay codes Kayentavenator as having a more propubic pelvis (~30 degrees from horizontal) than coelophysids (~45 degrees). This would be based off the angle of the pubic peduncle's articular surface, but as noted above, the preservation of this surface in Gay's illustration is in doubt.

The femoral head is coded as being subequally long and deep (in anterior/posterior view) while coelophysids' are coded as proximodistally elongate. However, the transverse width (from medial edge of femoral head to medial edge of shaft) is only 68% of the proximodistal height of the head, which is close to that in the kayentakatae holotype (63%). Since Coelophysis varies between 43% and 62%, a difference of 5% seems within plausible individual variation in kayentakatae. The anterior trochanter is aliform (as confirmed by Tykoski, 2005) while coelophysids' were incorrectly coded as absent. In actuality, many gracile coelophysoids (e.g. Dilophosaurus, Megapnosaurus) have aliform anterior trochanters as well. Gay codes coelophysids as having an anterior trochanter (contra the previous character) which does not extend proximally past the femoral head's ventral margin unlike Kayentavenator, but coelophysids' anterior trochanters do in fact extend past the femoral head's margin (e.g. kayentakatae- Rowe, 1989). Finally, the proximomedial fibular sulcus is coded as absent in coelophysids unlike Kayentavenator, but this feature is present in all adult coelophysids and was even made famous by kayentakatae.

In all, the characters which supposedly differ from coelophysids are miscodings or based on questionable morphologies (perhaps switched distal femora, possibly broken pubic peduncle, uncertain neural arch position). Supporting the placement of Kayentavenator in the Coelophysoidea is the presence of a divided articular facet on the pubic peduncle of the ilium, as illustrated by Tykoski.

Next up, is the Kayentavenator specimen a valid taxon of coelophysoid or a juvenile kayentakatae?

References- Rowe, 1989. A new species of the theropod dinosaur Syntarsus from the Early Jurassic Kayenta Formation of Arizona. Journal of Vertebrate Paleontology. 9, 125-136.

Perez-Moreno, Sanz, Sudre and Sige, 1993. A theropod dinosaur from the Lower Cretaceous of Southern France. Revue de Paleobiologie. 7, 173-188.

Tykoski, 1998. The osteology of Syntarsus kayentakatae and its implications for ceratosaurid phylogeny. Unpublished Masters Thesis, University of Texas at Austin. 217 pp.

Naish, 1999. Theropod dinosaur diversity and palaeobiology in the Wealden Group (Early Cretaceous) of England: Evidence from a previously undescribed tibia. Geologie en Mijnbouw. 78, 367-373.

Tykoski, 2005. Anatomy, ontogeny and phylogeny of coelophysoid theropods. PhD Dissertation. University of Texas at Austin. 553 pp.

Gay, 2010. Notes on Early Mesozoic theropods. Lulu Press. 44 pp.

Sunday, September 26, 2010

Please DON'T ignore any taxa - A rebuttal to O'Connor and Dyke

O'Connor and Dyke (2010) recently published a paper defending the validity of Cathayornis in relation to Sinornis, and thus contradicting Sereno et al. (2002).  The paper looks good and I feel a bit the fool for taking Sereno's statements at face value instead of examining the data myself.  They also examine the referred species (C. caudatus, C. aberransis and C. chabuensis) and come to largely similar conclusions as I did.  At the end of the paper, the authors make a number of observations and recommendations regarding taxonomic and descriptive practices for Mesozoic birds.  I agree with most of these.  We do need better diagnoses and more informative descriptions and illustrations, and I concur that Hou's 1997 book and the Dapingfangornis description are two of the worst offenders.  Yet I don't think this is as much as problem with the clade as it is with particular authors.  Chiappe's descriptions and diagnoses are generally excellent for instance, but Ji and Ji's papers leave something to be desired, even when they're on non-enantiornithines (e.g. Sinotyrannus, Sinosauropteryx, Protarchaeopteryx). 

Another issue the authors bring up are privately owned specimens, using Dalingheornis and Naish et al.'s (2007) Crato bird as examples. It's odd that Dalingheornis is used twice as an example of this, when it is said to be housed in Capital Normal University, AND O'Connor herself was a coauthor.  Maybe it has since been moved to a private collection, but even if so, authors can't be expected to predict future events.  O'Connor and Dyke state privately owned specimens are "unavailable to the scientific community, and thus rendering any interesting data they may have to contribute unverifiable and useless."  I'm no fan of private ownership of important fossil specimens, but unfortunately the world doesn't always give us ideal circumstances.  Note that publically owned specimens (e.g. Quetzalcoatlus) can be just as unavailable as any in a private collection and that privately owned specimens aren't always inaccessable.  But even ignoring that, information is information and having it is always better than not.  Even assuming a specimen is lost, casts are useful and even superior in some ways (as the authors note for Sinornis and Cathayornis), photos are still a form of information, and illustrations and descriptions are as well.  Not as useful as the real thing of course, but life is seldom ideal.

The authors are most concerned with the erection of taxa based on fragmentary types, but I don't think it is as big of a problem as they say.  O'Connor and Dyke point out "over a third of all known enantiornithines are named from bone fragments", which is true.  But looking at their table shows that these are almost exclusively two kinds of taxa.  Some are the earliest named enantiornithines (e.g. Avisaurus, Nanantius), when we simply didn't have complete specimens.  But most are from Soviet Asia (Explorornis, Lenesornis, Catenoleimus, etc.), and as anyone who's read Nessov's work knows, erecting taxa on fragments from the Bissekty Formation is not a problem unique to enantiornithines.  Moreover, some of the taxa the authors lament (e.g. Lectavis) are quite diagnostic, regardless of how fragmentary they are.

These are all fairly typical statements, but the part I'm most concerned about is the author's suggestion for dealing with these issues.  In addition to the urge for reviewers to do a better job (which I support), O'Connor and Dyke make the following horrific recommendation-

"When taxa are based on private material, or are for other reasons invalid, the scientific community should unify in excluding these ‘taxa’ when discussing the clade they are purported to belong to. This will hopefully discourage the continued practice of the erection of such taxa (e.g., Dalingheornis, Zhang et al., 2006)."

No, no, a thousand times no!  Place the word in scare quotes or not, any species whose description passes the rules of the ICZN is a valid taxon.  Maybe it's undiagnostic, maybe the description is horrid, but the name is out there based on an animal that existed, and thus constitutes real data.  A name cannot be un-done, and named taxa almost always carry useful information no matter how fragmentary.  Any discussion of enantiornithine locomotory variation that excludes Yungavolucris would be incomplete, as would any discussion of enantiornithine sacral morphology that excludes the Soviet synsacrum-based taxa.  And discussing these specimens without using their names would be confusing and petty.  More basically, science is not politics. We should always use all the information at our disposal, and not exclude some for purposes of affecting policy or changing behavior.  While scientists should of course try to create and enforce better policies in their field, the science itself should be above this.

References- Sereno, Rao and Li, 2002. Sinornis santensis (Aves: Enantiornithes) from the Early Cretaceous of Northeastern China. in Chiappe and Witmer (eds.). Mesozoic Birds - Above the Heads of Dinosaurs. University of California Press. 184-208.

Zhang, Hou, Hasegawa, O'Connor, Martin and Chiappe, 2006. The first Mesozoic heterodactyl bird from China. Acta Geologica Sinica. 80(5), 631-635.

Naish, Martill and Merrick, 2007. Birds of the Crato Formation. in Martill, Bechly and Loveridge (eds). The Crato Fossil Beds of Brazil: Window Into an Ancient World. Cambridge University Press. 525-533.

O'Connor and Dyke, 2010. A reassessment of Sinornis santensis and Cathayornis yandica (Aves: Enantiornithes). Records of the Australian Museum. 62, 7-20.

Saturday, September 11, 2010

Do theropods described in Science and Nature get fully described later?

At the request of Mike Taylor, here's an update and expansion of a post I wrote for the DML last year.  Basically, we have a system that rewards publishing in Nature and Science (the so-called tabloids) despite the fact papers in those journals are universally thought to be too short due to space restrictions.  The usual response is that Nature/Science papers are just meant to be preliminary announcements that will be followed by more detailed coverage later.  But how often does this actually happen? 

Easy enough to find non-neornithine theropods thanks to The Theropod Database.  Note I only included taxa which were first named in Nature and (new for this blog post) Science, not those (like Sinornithomimus) which were first announced in Nature but named elsewhere, nor those (like Protarchaeopteryx) which were first named in obscure journals then redescribed in Nature.  I didn't count instances like Shuvuuia, where Chiappe (2002) did describe and illustrate more than was done in Nature, but only in the context of a chapter describing all alvarezsaurids.  So while the skull was effectively redescribed (as it was the only complete alvarezsaurid skull known), comments on the postcrania are only mixed with descriptions of other taxa or generalized alvarezsaurid description.  I also didn't include Majungatholus, which is a theropod described as a pachycephalosaur in Nature, which was later synonymized with MajungasaurusMajungasaurus was redescribed in 2007 based mostly on new remains initially reported in 1998 in Science.  So ... uh... I guess that taxon counts as a win for Science/Nature.

Sereno, Forster, Rogers and Monetta, 1993. Primitive dinosaur skeleton from Argentina and the early evolution of Dinosauria. Nature. 361, 64-66.
Redescription in progress for over a decade for publication as a JVP monograph.

Xu, Clark, Mo, Choiniere, Forster, Erickson, Hone, Sullivan, Eberth, Nesbitt, Zhao, Hernandez, Jia, Han and Guo, 2009. A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature. 459, 940-944.
Not redescribed.

Charig and Milner, 1986. Baryonyx, a remarkable new theropod dinosaur. Nature. 324, 359-361.
Charig and Milner, 1997. Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey. Bulletin of the Natural History Museum of London (Geology). 53, 11-70.

Coria and Salgado, 1995. A new giant carnivorous dinosaur from the Cretaceous of Patagonia. Nature. 377, 224-226.
Not redescribed yet except for the braincase in 2002 (Coria and Currie).

Buffetaut, Suteethorn and Tong, 1996. The earliest known tyrannosaur from the Lower Cretaceous of Thailand. Nature. 381(6584), 689-691.
Not redescribed.

Xu, Norell, Kuang, Wang, Zhao and Jia, 2004. Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids. Nature. 431, 680-684.
Not redescribed.

Xu, Clark, Forster, Norell, Erickson, Eberth, Jia and Zhao, 2006. A basal tyrannosauroid dinosaur from the Late Jurassic of China. Nature. 439, 715-718.
Not redescribed.

Gohlich and Chiappe, 2006. A new carnivorous dinosaur from the Late Jurassic Solnhofen archipelago. Nature. 440, 329-332.
Gohlich, Tischlinger and Chiappe, 2006. Juravenator starki (Reptilia, Theropoda) ein neuer Raubdinosaurier aus dem Oberjura der Sudlichen Frankenalb (Suddeutschland): Skelettanatomie und Weichteilbefunde. Archaeopteryx. 24, 1-26.

Dal Sasso and Signore, 1998. Exceptional soft tissue preservation in a theropod dinosaur from Italy. Nature. 392, 383-387.
Described in depth in Signore's thesis, which isn't published.  Dal Sasso and Maganuco are writing a monograph which Auditore said would be out in 2009 or early 2010, but it seems to be delayed.

Perez-Moreno, Sanz, Buscalioni, Moratalla, Ortega and Rasskin-Gutman, 1994. A unique multitoothed ornithomimosaur dinosaur from the Lower Cretaceous of Spain. Nature. 370, 363-367.
Redescribed in Perez-Moreno's unpublished thesis.

Chiappe, Norell and Clark, 1998. The skull of a relative of the stem-group bird Mononykus. Nature. 392, 275-278.
Not redescribed.

Perle, Norell, Chiappe and Clark, 1993. Flightless bird from the Cretaceous of Mongolia. Nature. 362, 623-626.
Perle, Chiappe, Barsbold, Clark and Norell, 1994. Skeletal morphology of Mononykus olecranus (Theropoda: Avialae) from the Late Cretaceous of Mongolia. American Museum Novitates. 3105, 1-29.

Kirkland, Zanno, Sampson, Clark and DeBlieux, 2005. A primitive therizinosauroid dinosaur from the Early Cretaceous of Utah. Nature. 435, 84-87.
Zanno, 2010. Osteology of Falcarius utahensis: Characterizing the anatomy of basal therizinosaurs. Zoological Journal of the Linnaean Society. 158, 196-230.

Xu, Tang and Wang 1999. A therizinosauroid dinosaur with integumentary structures in China. Nature. 399, 350-354.
Not redescribed.

Xu, Cheng, Wang and Chang, 2002. An unusual oviraptorosaurian dinosaur from China. Nature. 419, 291-293.
Balanoff, Xu, Kobayashi, Matsufune and Norell, 2009. Cranial osteology of the theropod dinosaur Incisivosaurus gauthieri (Theropoda: Oviraptorosauria). American Museum Novitates. 3651, 35 pp.

Ji, Currie, Norell and Ji, 1998. Two feathered dinosaurs from northeastern China. Nature. 393, 753-761.
The type specimens haven't been redescribed, though Zhou et al. (2000) did describe others in more depth.

Xu, Tan, Wang, Zhao and Tan, 2007. A gigantic bird-like dinosaur from the Late Cretaceous of China. Nature. 844-847.
Not redescribed.

Xu and Norell, 2004. A new troodontid dinosaur from China with avian-like sleeping posture. Nature. 431, 838-841.
Not redescribed.

Xu, Norell, Wang, Makovicky and Wu, 2002. A basal troodontid from the Early Cretaceous of China. Nature. 415, 780-784.
Not redescribed.

Elzanowski and Wellnhofer, 1992. A new link between theropods and birds from the Cretaceous of Mongolia. Nature. 359, 821-823.
Elzanowski and Wellnhofer, 1993. Skull of Archaeornithoides from the Upper Cretaceous of Mongolia. American Journal of Science. 293-A, 235-252.

Makovicky, Apesteguía and Agnolín, 2005. The earliest dromaeosaurid theropod from South America. Nature. 437, 1007-1011.
Not redescribed.

Novas and Puerta, 1997. New evidence concerning avian origins from the Late Cretaceous of Patagonia. Nature. 387: 390-392.
Not redescribed except the ilium by Novas (2004).

Xu, Wang and Wu, 1999. A dromaeosaurid dinosaur with filamentous integument from the Yixian Formation of China. Nature. 401, 262-266.
Not redescribed except for the skull (Xu and Wu, 2001) and the pes (Xu and Wang, 2000).

Xu, Zhou and Wang, 2000. The smallest known non-avian theropod dinosaur. Nature, 408, 705-708.
The holotype has not been redescribed, though two other specimens were monographed (Hwang et al., 2002).

Microraptor gui
Xu, Zhou, Wang, Kuang, Zhang and Du, 2003. Four-winged dinosaurs from China. Nature. 421, 335-340.
Not redescribed.

Novas and Pol, 2005. New evidence on deinonychosaurian dinosaurs from the Late Cretaceous of Patagonia. Nature. 433, 858-861.
Not redescribed.

Zhang, Zhou, Xu, Wang and Sullivan, 2008. A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers. Nature. 455, 1105-1108.
Not redescribed.

Zhou and Zhang, 2002. A long-tailed, seed-eating bird from the Early Cretaceous of China. Nature. 418, 405-409.
Not redescribed.

Confuciusornis dui
Hou, Martin, Zhou, Feduccia and Zhang, 1999. A diapsid skull in a new species of the primitive bird Confuciusornis. Nature. 399, 679-682.
Not redescribed.

Walker, 1981. New subclass of birds from the Cretaceous of South America. Nature. 292, 51-53.
Not redescribed.

Forster, Chiappe, Sampson, Krause, 1996. The first Cretaceous bird from Madagascar. Nature. 382, 532-534.
Forster, Chiappe, Krause and Sampson, 2002. Vorona berivotrensis, a primitive bird from the Late Cretaceous of Madagascar. 268-280. in Chiappe and Witmer (eds.). Mesozoic Birds: Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.

Sanz, Chiappe, Perez-Moreno, Buscalioni, Moratalla, Ortega and Poyato-Ariza, 1996. An Early Cretaceous bird from Spain and its implications for the evolution of avian flight. Nature. 382, 442-445.
Sanz, Pérez-Moreno, Chiappe and Buscalioni, 2002. The Birds from the Lower Cretaceous of Las Hoyas (Privince of Cuenca, Spain). pp 209-229. in Chiappe and Witmer (eds.). Mesozoic Birds: Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.

Molnar, 1986. An enantiornithine bird from the Lower Cretaceous of Queensland, Australia. Nature 322 736-738.
Not redescribed.

Norell and Clarke, 2001. Fossil that fills a critical gap in avian evolution. Nature. 409, 181-184.
Clarke and Norell, 2002. The morphology and phylogenetic position of Apsaravis ukhaana from the Late Cretaceous of Mongolia. American Museum Novitates. 3387, 1-46.

So that's Nature, but what about Science?

Hammer and Hickerson, 1994. A crested theropod dinosaur from Antarctica. Science. 264:828-830.
Smith, Makovicky, Hammer and Currie, 2007. Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution. Zoological Journal of the Linnean Society. 151, 377-421.

Sereno, Dutheil, Iarochene, Larsson, Lyon, Magwene, Sidor, Varricchio and Wilson, 1996. Predatory dinosaurs from the Sahara and Late Cretaceous faunal differentiation. Science. 272(5264), 986-991.
Not redescribed.

Bonaparte, 1979. Dinosaurs: A Jurassic assembalge from Patagonia. Science. 205, 1377-1379
Bonaparte, 1986. Les Dinosaures (Carnosaures, Allosauridés, Sauropodes, Cétiosauridés) du Jurassique moyen de Cerro Cóndor (Chubut, Argentine). [The Middle Jurassic dinosaurs (carnosaurs, allosaurids, sauropods, cetiosaurids) from Cerro Cóndor (Chubut, Argentina).] Annales de Paléontologie. Paris, France. 72, 247-289.

Sereno, Wilson, Larsson, Dutheil and Sues, 1994. Early Cretaceous dinosaurs from the Sahara. Science. 266, 267-271.
Not redescribed.

Sereno, Beck, Dutheil, Gado, Larsson, Lyon, Marcot, Rauhut, Sadleir, Sidor, Varricchio, Wilson and Wilson, 1998. A long-snouted predatory dinosaur from Africa and the evolution of the spinosaurids. Science. 282(5392), 1298-1302.
Not redescribed.

Sereno, Tan, Brusatte, Kriegstein, Zhao and Cloward, 2009. Tyrannosaurid skeletal design first evolved at small body size. Science. 326(5951), 418-422.
Not redescribed.

Choiniere, Xu, Clark, Forster, Guo and Han, 2010. A basal alvarezsauroid theropod from the Early Late Jurassic of Xinjiang, China. Science. 327, 571-574.
Not redescribed.

Turner, Pol, Clarke, Ericson and Norell, 2007. A basal dromaeosaurid and size evolution preceding avian flight. Science. 317, 1378-1381.
Not redescribed.

Forster, Sampson, Chiappe and Krause, 1998. The theropod ancestry of birds: New evidence from the Late Cretaceous of Madagascar. Science. 279, 1915-1919.
Not redescribed.

Zhang and Zhou, 2000. A primitive enantiornithine bird and the origin of feathers. Science. 290, 1955-1959.
Not redescribed.

Sereno and Rao, 1992. Early evolution of avian flight and perching: New evidence from Lower Cretaceous of China. Science. 255, 845-848.
Sereno, Rao and Li, 2002. Sinornis santensis (Aves: Enantiornithes) from the Early Cretaceous of Northeastern China. pp 184-208. in Chiappe and Witmer, (eds.). Mesozoic Birds – Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London. 

So, of all 33 theropods described in Nature, 25 (76%) have yet to be fully described in a published work.  Of all 11 theropods described in Science, 8 (73%) have yet to be fully described.  So in total, 75% haven't been redescribed.

To be a bit more fair, of the 25 taxa described at least a decade ago, 17 (68%) have yet to be fully described. Hmm... doesn't really change the ratio.

Friday, September 10, 2010

Concavenator Part II - Becklespinax comparison, ulnar muscle details and a last lunch

It seems Naish had the same ideas I did regarding the similarity to Becklespinax and the supposed ulnar quill knobs being part of an intermuscular line.  That we both came up with these conclusions so quickly leads me to wonder why none of the article's reviewers did, or if they did, why they weren't taken into account by the authors. In fact, Becklespinax's description was cited (as reference 26 to an "undetermined tetanuran") though Ortega et al. incorrectly say "none of these [high-spined taxa] has elongated neurapophyses restricted to two presacral dorsal vertebrae."  Naish noted he proposed the same kind of short posterior dorsal sail for Becklespinax in 2007, and indeed the idea goes back to the Crystal Palace Megalosaurus which were given an anterior hump based on the Becklespinax material.  In regard to the ulnar morphology, Jura/Jason noted on the DML that the authors didn't examine any other explanations for the ulnar ridge and knobs.  He's correct to state that we shouldn't be so quick to accept new hypotheses without testing, and I have a feeling we'll see Concavenator inappropriately used as evidence for carnosaurian feathers without question for years to come.

In any case, what does a comparison of Concavenator with Becklespinax reveal?  Becklespinax has "tall neurapophyses of the eleventh and twelfth dorsal vertebrae (five times the height of the centra)", which is listed in Concavenator's diagnosis.  It also has "accessory centrodiapophyseal lamina on the transverse processes of the posterior dorsal vertebrae" on the last two dorsals, which is listed as another diagnostic feature that is also present in baryonychines.  Naish noted both lack pleurocoels, but this is normal for theropod posterior dorsals and is only untrue in certain groups like carcharodontosaurids, tyrannosaurids and caenagnathoids.  In regard to Becklespinax, Olshevsky (1991) stated "The firm contact between the apexes of the neural spines of vertebrae #9 and 10 (and, presumably, later vertebrae in the series) is a diagnostic feature of the specimen that occurs in no other known theropod genus."  This is also found in Concavenator, in which the anterior  neural spine actually seems to overlap the posterior one at their tips.  He also stated that "It is possible
that the neural spine of vertebra #8 is not broken off at the top but is naturally shorter than die spine of #9. This would constitute another very strong diagnostic feature of the genus, but it requires physical examination of the specimen before it can be confirmed."  This is found in Concavenator as well, to an even greater extreme.  Naish (online, 2007) noted Becklespinax has a spine table on its posterior two dorsals, but the condition in Concavenator has not been reported yet.

Dorsal vertebrae 10-12 of Concavenator (left, after Ortega et al., 2010) and Becklespinax (right, after Owen, 1856).  Sediment around neural spines removed to show shape better.  Red dotted line in Concavenator indicates possible real outline of twelfth neural spine, red dotted line in Becklespinax indicates possible dorsal limit to tenth neural spine.

So simply based on the published diagnoses for each genus, Becklespinax and Concavenator are indistinguishable.  Naish correctly stated Becklespinax is Valanginian (not Barremian like I wrote), which does make it a bit earlier stratigraphically than Concavenator.  Still, stratigraphy is frowned upon as a diagnostic character, or else Triceratops would be Agathaumas and such.  So we'll have to look in greater detail at the two genera, which isn't easy because Concavenator was described in Nature (so has an extremely brief description, though Ortega et al. do provide several excellent close up photos in the supplementary information) and Becklespinax hasn't been redescribed in a modern context (though Naish has done so in his unpublished thesis).  Also hindering matters is the fact Concavenator's neural arches are largely hidden by the dorsal ribs.  The exposed centra and diapophyseal areas are identical from the photos (which isn't saying much), but the neural spines do differ.  In Becklespinax, the tenth spine is taller and there is much more space between the eleventh and twelfth spines.  Also, in Becklespinax the neural spines are distally expanded while they are distally tapered in Concavenator.  I do wonder how much of this is real in Concavenator, especially in the twelfth spine.  That one has a strongly notched posterior edge that isn't matched at all by the life restoration's smooth triangular fin, leading me to wonder if its spine was distally expanded like Becklespinax's in life.  In all three characters, Becklespinax is closer to the condition in basal carnosaurs such as Sinraptor, which matches stratigraphy in a simplistic way.

Based on these comparisons, for the moment I consider both taxa valid, though closely related.  Whether they are congeneric or not is a subjective decision of course, but I don't think sinking Concavenator is a better idea than doing so to Effigia or any of the numerous genera Paul synonymized in his new book.  It's possible the distinguishing characters are individual or sexual variation, especially if the hump/sail was for display, but it's hard to know with a stratigraphically separated sample size of two.

Based on the ulnar musculature of modern alligators (Meers, 2003), the intermuscular line in Concavenator seems to be between the flexor ulnaris and the extensor carpi radialis brevis (Haro, DML).  This is shown in the figure below where you can see how anteriorly placed the line and knobs are in Concavenator compared to the quill knobs of Velociraptor and birds.  Note too that Concavenator's ulna is shown in anterolateral view based on the position of the radial articular surface (outlined in all three in green).  Thus the line would appear to be even further anteriorly positioned if the bone were in the same perspective as the Alligator and Velociraptor ulnae.  I've sketched in a rough guide to where the flexor ulnaris and the extensor carpi radialis brevis would be in Concavenator.  Based on the topographic similarity, I think we can be fairly certain the structure is an intermuscular line and not quill knobs.

Ulnae in lateral view of Alligator (top, after Meers, 2003), Concavenator (middle, after Ortega et al., 2010) and Velociraptor (bottom, after Turner et al., 2007). Radial articular surface outlined in green, relevent muscle placement added to Concavenator in colors matching Alligator, quill knob positions added in red for Velociraptor.
A final thought- has anyone else noticed the series of twenty or so small vertebrae illustrated in the gut area of Concavenator?  They seem too short for distal caudals, especially with their high neural spines and transverse processes.  I can only assume they are stomach contents, but it's odd the authors didn't mention it.

References- Owen, 1856. Monograph on the fossil Reptilia of the Wealden Formation. Part IV. Palaeontological Society Monographs. 10, 1-26.

Olshevsky, 1991. A Revision of the Parainfraclass Archosauria Cope, 1869, Excluding the Advanced Crocodylia. Mesozoic Meanderings. 2, 196 pp. 

Meers, 2003. Crocodylian forelimb musculature and its relevance to Archosauria. The Anatomical Record. Part A, 274A, 891-916.

Naish, online 2007.

Turner, Makovicky and Norell, 2007. Feather quill knobs in the dinosaur Velociraptor. Science. 317, 1721.

Ortega, Escaso and Sanz, 2010. A bizarre, humped Carcharodontosauria (Theropoda) from the Lower Cretaceous of Spain. Nature. 467, 203-206. 

Thursday, September 9, 2010

Concavenator - feathers, Becklespinax and how not to delete taxa

So Concavenator is all the rage, and having just received the paper from Holtz (thanks!), I figured I'd share a few opinions.

First, the supposed feather quill knobs on the ulna.  I have no problem with feathered carnosaurs, or any sort of feathered dinosaur really.  But the knobs are in a line that while described as "posterolateral", is really more anterolateral based on the photo.  They extend from the distal tip of the brachial fossa area to the articular facet for the radius, which aren't areas particularly close to the skin.  I think its more likely an intermuscular line.

Right forearm of Concavenator corcovatus holotype MCCM-LH 6666 in lateral view.  Arrows point to the supposed quill knobs (after Ortega et al., 2010).

Second, I'm very surprised no one has yet mentioned Becklespinax in relation to Concavenator.  Both are Barremian carnosaurs from Europe.  More importantly, Becklespinax is known from three dorsal vertebrae, two with high spines in contact dorsally and the most anterior one with a naturally short spine.  That's diagnostic and just like Concavenator.  Seems like good evidence for a close relationship, though I would have to examine them in more detail to have an opinion on their synonymy.

Finally, a plea to perform phylogenetic analyses better.  The authors deleted the fragmentary taxa from the analysis before running it, but this is a poor way to do things.  If you must delete taxa to improve resolution (and studies have shown fragmentary taxa don't necessarily cause more polytomies as long as they have unique character combinations), do it AFTER the analysis is run.  That way, the taxa will still affect the topology.  As it is, the phylogeny in the paper is misleading because it places Concavenator as a basal carcharodontosaurid (in their usage) more derived than Eocarcharia, but this is only one of three different placements if Eocarcharia is included.  And who knows what the tree would look like if Xuanhanosaurus, Poekilopleuron, Piveteausaurus, Streptospondylus, Chilantaisaurus and Orkoraptor weren't deleted.

Ortega, Escaso and Sanz, 2010. A bizarre, humped Carcharodontosauria (Theropoda) from the Lower Cretaceous of Spain. Nature. 467, 203-206.

Wednesday, September 1, 2010

Ceratosaurian ornithomimosaurs - another crazy idea?

The first taxon to be added to Ceratosauria after Ceratosaurus itself was Ornithomimus (Marsh, 1895).  While this version of Ceratosauria has been long forgotten since Gauthier resurrected the name in 1986 for Ceratosaurus and coelophysoids, is it possible Marsh was on to something?  While recoding Holtz's (1994) matrix, I started noticing the coelurosaur-like characters of Elaphrosaurus.  For instance, the anterior cervical centra have very low anterior articular surfaces, there is no post-obturator notch on the ischium, the pubis lacks an obturator foramen, and the fourth trochanter is reduced.  Of course there are loads of more basal characters too, which is why it still clades in Ceratosauria in good analyses like Rauhut's (2003).  But what if we took another approach and placed ornithomimosaurs next to it in Ceratosauria instead?  Crazy, you say?  Probably, but it could help explain some otherwise incongruous features of ornithomimosaurs-

- Basal taxa like Pelecanimimus and Shenzhousaurus have very long antorbital fossae, and Shenzhousaurus has a longer portion of it taken up by the antorbital fenestra than most other coelurosaurs.
- Ornithomimosaurs' supposed maxillary fenestrae are usually small, not necessarily invasive, and resemble the sub-fossae of taxa like Ceratosaurus and Carnotaurus in being dorsal/ventral to their promaxillary fenestra.  Senter (2007) doubted their homology to maxillary fenestrae.
- Pelecanimimus is unlike coelurosaurs closer to birds than tyrannosaurids in having lacrimal horns.
- Ornithomimosaurs are like Limusaurus and coelophysoids in having reduced axial parapophyses and diapophyses.
- The perhaps basalmost known ornithomimosaur Deinocheirus has a short posteroventral coracoid process, unlike other maniraptoriforms.
- The humeri are straight with reduced deltopectoral crests, of course.
- The small carpals without obvious articular surfaces make more sense in a ceratosaur than a coelurosaur.
- Deinocheirus has a manual phalanx III-3 shorter than III-1 + III-2.
- The brevis fossa is broad and triangular unlike most coelurosaurs, but like non-tetanurines.
- The ilium's posterior edge is notched as in ceratosaurs.
- The ilium has a peg-in-socket articulation with the ischium in both groups.
- The pubis is directed further foreward than in most coelurosaurs.
- Shenzhousaurus seems to have an obturator foramen in its ischium, as in Limusaurus.
- The ischial boot is large as in ceratosaurs, but unlike any coelurosaur.

That's all great, but don't ornithomimosaurs have a ton of tetanurine, avetheropod, coelurosaur and maniraptoriform characters?  Well sure they have some, like fourth manual digit absent and metatarsal III proximally reduced.  But it's not often realized just how many features usually thought to be exclusive to coelurosaurs are also/already found in more basal taxa.  Ceratosaurus has pneumatized paroccipital processes.  Majungasaurus has a palatine-pterygoid subsidiary fenestra.  Ceratosaurs have distal caudal prezygapophyses over half of central length.  Majungasaurus has only eighteen caudals with transverse processes, similar to Tyrannosaurus and CompsognathusCarnotaurus has ossified sternal plates, which are otherwise only known in Baryonyx among non-maniraptoriforms.  Many ceratosaurs have tall astragalar ascending processes, and they've long been recognized as having large pubic boots and aliform anterior trochanters.

Unfortunately, a published matrix to test these ideas in doesn't yet exist.  While Xu et al.'s (2009) matrix (based largely on Smith et al.'s) would seem to be a good candidate since it includes Elaphrosaurus, Limusaurus, Ceratosaurus, Majungasaurus, Shenzhousaurus and an ornithomimid (though lacking Pelecanimimus and Deinocheirus), their habit of not coding taxa for "irrelevent" characters means they'll never find support for heterodox topologies such as this.  Majungasaurus is miscoded as lacking the subsidiary fenestra, Shenzhousaurus is miscoded as having a small antorbital fenestra within the fossa, ornithomimosaurs' possible maxillary fenestrae are assumed to be homologous to tetanurines', ornithomimids are coded as having large axial parapophyses and not coded at all for axial diapophyses, ornithomimosaurs aren't coded for distal carpal size or fusion, the ornithomimid wasn't coded for the postacetabular notch, Shenzhousaurus was miscoded as having an obturator process, the ornithomimid was miscoded as having a post-obturator notch, both ornithomimosaurs were miscoded as lacking an ischial boot, and both Elaphrosaurus and ornithomimosaurs were miscoded as having stout, well-developed fourth trochanters.