Monday, December 20, 2010

Herbivorous maniraptoriforms- Analysis criticism

Zanno and Makovicky just published a paper (from Zanno's thesis) presenting a quantitative and statistical analysis of the acquisition and distribution of traits associated with herbivory in coelurosaurs.  Basically they found that most maniraptoriforms except dromaeosaurids and (at least) derived troodontids weren't hypercarnivores.  No big surprise there, but it's an interesting concept to analyze.

On a basic level, I would have liked more evidence the traits used are actually associated with omnivory/herbivory.  For instance the bald eagle has several of the characters used-
- decurved anterior dentary, creating anterior gap between jaws.
- ventrally concave dentary.
- dentary exhibits tooth loss.
- premaxilla edentulous.
- mandibular symphysis fused.
- ischium over 66% of pubic length.
- opisthopubic pelvis.
- more than ten cervical vertebrae.
I think it's important to do a statistical study of dentary curvature/concavity, ischial length, cervical number, etc. in living birds to see if a correlation exists before assuming a correlation to study the diets of extinct taxa.  An elongate ischium is found in most non-maniraptorans except coelophysids, so its inclusion is especially confusing.

Yet even if we assume the traits correlate with herbivory, there are issues with the data used.  In figure 2 Yanornis is shown as having extrinsic evidence of herbivory while Confuciusornis is left with an ambiguous entry.  Yet both taxa are known from specimens preserving fish remains, as the supplementary information table S1 correctly indicates.  By their rules in table S1, Confuciusornis should be marked as having character 8 (evidence of carnivory: present only) since it has character 7 (vertebrate gut content: present only), which would then make it marked as lacking character 9 (extrinsic evidence of herbivory).  Similarly, Yanornis should be marked as having character 8, which would force 9 to be polymorphic since it also preserves direct evidence of herbivory.

There's also more of our friend the incompletely coded matrix.  Looking at Confuciusornis and Yanornis for instance since we're already dealing with them, neither is coded as lacking a U-shaped symphysis.  Yanornis isn't coded for its unserrated premaxillary teeth, densely packed teeth or short ischium.  Strangely, neither characters 1 nor 3 are coded for any taxon in the matrix. 

Also, Confuciusornis is miscoded as having a decurved anterodorsal dentary margin, lacking a ventrally displaced mandibular glenoid and having an ischium over 66% of pubic length.  It's also coded as lacking an inset dentary tooth row, conical anterior dentary and+or premaxillary teeth, elongate premaxillary teeth, unserrated premaxillary teeth, lanceolate cheek teeth, recurved teeth, ziphodonty, heterodont dentition, procumbant premaxillary teeth or having replacement waves between teeth, but all of these should be inapplicable since it lacks teeth.  Yanornis is miscoded as lacking tooth recurvature.

This is out of 31 characters, mind you.  So that's 21 wrong codings out of 62.  Note too there are unecessary characters such as "dentary exhibits tooth loss", when the list already contains "rostral dentary exhibits tooth loss" and "caudal dentary exhibits tooth loss."  Also "rostral teeth (premaxillary or dentary) conical to subconical" when it contains "premaxillary teeth conical or subconical (e.g., “incisiform”)" and "rostralmost dentary teeth conical: absent (0), present (1)." 

So while I don't doubt the general observation that maniraptoriforms were more herbivorous than most other theropods, I'm skeptical of the character distributions and statistics.

Reference- Zanno and Makovicky, 2010. Herbivorous ecomorphology and specialization patterns in theropod dinosaur evolution. PNAS Early Edition. 6 pp. doi 10.1073/pnas.1011924108

Thursday, December 16, 2010

Adventures in Not Coding- Marasuchus by Smith et al.

I've complained about the recent trend to not code taxa for characters in phylogenetic analyses here before.  Today I thought I'd show you an example.

The paper is Smith et al.'s (2007) influential basal theropod analysis in the Cryolophosaurus monograph.  Holtz said on the DML that it was "truly good stuff, and I strongly suspect that they have better captured the actual phylogeny of basal theropods than most previous studies."  The paper includes Makovicky and Currie as coauthors- two people who know their stuff and have access to specimens.  There's no excuse to make obvious mistakes.

The taxon is Marasuchus, the outgroup of the analysis.  This basal dinosauriform includes the more complete specimens once referred to Lagosuchus and has been described by Bonaparte (1975) and Sereno and Arcucci (1994) in addition to the briefer original descriptions by Romer (e.g. 1972).  This is a classic OTU for dinosaur analyses, used in papers by Rauhut, Ezcurra, Novas and others.  So there's plenty of information on the taxon available in easily accessed journals like JVP.

What follows are Smith et al.'s codings compared to my codings, divided by anatomical section.  Note somebody with access to the specimens themselves would be able to code even more than I could. 

Smith et al.- ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? ???0???00? 00??-???00 ?0???????? ?????????? ?????????? ?
Me- ?0???????? ?????????? ?0?????00- ?0??10???? ?????????? ?????????? ?????????? ?????????? 0????????0 0??????00? 0000-?1?01 ?0???????? ?????????? ?????????? ?

Cranially, Marasuchus is known from a maxilla and braincase.  Note the first section of coded characters in my row pertains to the maxilla, which went completely uncoded by Smith et al..  The second section pertains to the braincase, and here I was also able to code more.  Altogether Smith et al. coded 9 characters, while I coded 22.

Smith et al.- ?00?????- ??0?0??0?0 0?00????0? ?????????0 0???-??0?? ?0??????0? ?????
Me- 0110?0--- 0-0?10000- 01000??010 -?00010?00 100?1010?0 0p00000000 00???

Axially, Smith et al.'s laziness really shows.  Marasuchus preserves an almost complete vertebral column, yet Smith et al. only coded a few of the characters.  What's confusing too is that it's not the obvious characters which were coded.  Things like axis, cervical and dorsal pleurocoels absent, and amphicoelous cervical centra should be second nature to code for anyone even vaguely familiar with the taxon, but then there are characters like "cervical prespinal fossa narrow" which WERE coded.  Now having a wide prespinal fossa is an abelisaurid character, so nobody describes the state in something like Marasuchus, and Marasuchus' vertebrae have only been illustrated laterally as far as I know (not anteriorly, as you'd need to see the prespinal fossa).  It's not that I doubt Marasuchus would have a narrow fossa if examined, but since almost every non-coelurosaur with preserved cervicals is coded for this obscure character, and the matrix certainly doesn't show signs of rigorous coding in general, I'm suspicious.  Another issue is that some of the uncoded characters are important to code in Marasuchus, like the absence of hyposphenes or the presence of only two sacrals.  Again these are things anyone with even a passing interest in dinosaur origins would be aware of, as they are classic characters excluding it from Saurischia and Dinosauria respectively.  Without coding Marasuchus, the state "2 sacrals" is useless, as all other taxa have more (even the miscoded Saturnalia).  In the axial area, 17 characters were coded by Smith et al., but 54 could be coded by me.

The two integumentary characters cannot be coded, of course.

Smith et al.- ??? ?????????
Me- ??? 10010?000

In the pectoral girdle, Marasuchus preserves a scapulocoracoid.  Smith et al. didn't bother coding it at all.  Even obvious characters like the broad scapular blade, which was explicitly noted by Sereno and Arcucci to be an autapomorphy of the taxon.  So 0 coded by them, and 8 by me.

Smith et al.- ? ????????0? ?????????? ?????????? ?
Me- 0 00p?000?0? ?????????? ?????????? ?

In the forelimb, Marasuchus preserves a humerus, radius and ulna.  Smith et al. bothered to code one character- radius over half humeral length.  At least it's an obvious character this time.  That's 1 coded by them, and 8 by me.

Smith et al.- ????????? 0??0??1p00 00-00??0?? ?00?00???? ?
Me- 0000010?1 00020p0100 ---00p?000 --00?0?00? 0

Marasuchus preserves an essentially complete pelvis.  This situation is rather like the axial skeleton.  Again, obvious characters are left uncoded- propubic pelvis, short preacetabular process, no post-obturator notch.  And again, some are important.  If Marasuchus isn't coded as lacking a brevis fossa, why even have the character?  Everything else in the matrix has one (except Confuciusornis, which is nonsensically coded as inapplicable), so without coding Marasuchus the character's useless.  Of pelvic characters, Smith et al. code 16 and I code 35.

Smith et al.- ??0000000 0000001?0? 0?0????000 00000000?0 0000???0?0 00r????
Me- 001000000 000000100- 0000010000 0101000000 0000001100 001?0??

Finally, a decently coded area.  There are certainly some absences, like the obvious anteromedially oriented femoral head and absent fibular crest of the tibia, and none of the fibular characters are coded.  But overall it looks like someone actually tried in this area.  Smith et al. code 38 and I code 53.

In all, Smith et al. coded 81 characters while I coded 180.  That leaves 91 characters uncoded. So they only coded 45% of what was possible using the literature, and an even smaller percentage of what's possible with the specimens in hand.  You might not think it's important to code the outgroups, but you'd be wrong.  The major conclusion of this paper was that Crylophosaurus and other dilophosaurs were closer to neotheropods than coelophysoids, but this depends on having the polarity for characters in basal Avepoda correct.  I can tell you now that even though I haven't worked my way through most of the matrix yet, just adding the codings for Marasuchus, Silesaurus and some for Herrerasaurus has changed the results to give a huge polytomy in basal Avepoda between coelophysoids, Zupaysaurus, dilophosaurids and neotheropods.  Who knows how that will change though, as I note that "Dilophosaurus" sinensis wasn't coded at all postcranially, for instance. 

I'd honestly like to know how this happens.  This isn't some obscure foreign paper by ignorant beginners, it's a landmark paper in a high tier journal by experts in the field.  Yet what I've described here is unacceptable.  If you're publishing a phylogenetic analysis, please code your taxa.  If you're reviewing/editing a paper, please check a taxon or two in the matrix.  And if you find uncoded taxa, send the paper back.  Because coding only half the available data makes the resulting cladogram worthless.

Reference- 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.

Tuesday, December 14, 2010

The Myth of Martinavis

After 28 years, the monograph on Lecho enantiornithines has finally been published (Walker and Dyke, 2009).  This follows the shorter paper by Walker et al. (2007), which assigned many Lecho remains to their new genus Martinavis.  Now in addition to M. cruzyensis from France and M. vincei from Argentina, we also have M. saltariensis, M. minor and M. whetstonei living alongside M. vincei, plus an unnamed specimen from the US.  At first glance, this seems to be an amazing diversity for an enantiornithine genus, but some further digging indicates trouble for Martinavis.

Walker et al.'s diagnosis for Martinavis is sprawling, but most of the characters are just enantiornithine synapomorphies- proximal margin of humerus concave in its central portion, rising both ventrally and dorsally on either side; bicipital crest prominent; ventral surface of bicipital crest bearing a small fossa for muscle attachment; proximally L-shaped humeral head; well-marked depression underneath the proximal head of the humerus; weakly developed distal condyles; flat distal end that is not deflected dorsally.

The pneumotricipital fossa is no wider in vincei, saltariensis or minor than Elbretornis, Enantiornis, Gurilynia, Halimornis or Otogornis, and is narrow in cruzyensis and whetstonei. It is wide in the American specimen KU-NM-37 though.

The lack of a perforated ventral tubercle is plesiomorphic and also present in such taxa as Halimornis and Eoalulavis.

Most enantiornithine deltopectoral crests could be described as "flat and broad", while the stated lack of ventral curvature in the crest is difficult to understand since it projects dorsally in enantiornithines.

The lack of a marked distal angle between the deltopectoral crest and shaft distally is primitive and also seen in such taxa as Eoalulavis, Eocathayornis, Hebeiornis, Otogornis, Pengornis and Cathayornis, but is absent in saltariensis and not determinable in KU-NM-37.

The bicipital crest in cruzyensis and vincei is no smaller than in Gurilynia, while KU-NM-37, minor, saltariensis and whetstonei have large crests.

The bicipital crest is indeed more anteriorly angled in vincei and KU-NM-37 than Elbretornis, Enantiornis, Halimornis or Gurilynia, but is less angled than Elsornis. Supposed Martinavis species minor, saltariensis and whetstonei have less angled crests.  The condition in cruzyensis is not illustrated, though stated to be less than vincei at least. 

"Ventral margin of bicipital crest small" is a confusing statement, and the ventrally placed bicipital fossa is also present in Elbretornis, Gurilynia and Halimornis while those of M. cruzyensis, saltariensis and minor are anteroventrally placed.

The ventral condyle is as poorly developed in Elbretornis, Elsornis, Eocathayornis, Kizylkumavis and Cathayornis. Note neither this nor the next three characters can be evaluated in minor, whetstonei or KU-NM-37. 

Alexornis, Elbretornis, Elsornis, Kizylkumavis and Otogornis lack both scapulotricipital and humerotricipital grooves as well.

The ventral epicondyle is as large and distally projected in Kizylkumavis and probably Alexornis.

A transversely oriented dorsal condyle is present in almost all enantiornithines, even Elbretornis (contra Walker and Dyke)

Walker et al. also included a differential diagnosis, though it repeats some characters of the general diagnosis (anteriorly angled bicipital crest; deltopectoral crest smoothly angled; transversely oriented dorsal condyle) and has another which contradicts the general diagnosis (small entepicondyle). Of the remaining characters, the shaft is actually less gracile than Enantiornis (and most other enantiornithines), not more. A laterally positioned ectepicondyle is present in all enantiornithines.  Walker and Dyke do not add further characters to the diagnosis.

In conclusion, species referred to Martinavis do not share any apomorphies not found in numerous other enantiornithines.  Worse, the type species lacks two of the supposed diagnostic characters, saltariensis lacks four, both minor and whetstoni lack at least three, and the American specimen lacks at least one.  Walker et al. should have really made M. vincei the type species, since it seems most representative.  Walker and Dyke refer numerous additional postcranial elements to Martinavis sp. based on size, but since there's no evidence that genus was present in Argentina, it seems best to keep these as Enantiornithes indet..  The small size of some means they probably belonged to minor or whetstonei, while the larger may have belonged to vincei or saltariensis.

Martinavis - The Cathayornis of the Late Cretaceous. ;)

References- Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.

Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.

Friday, December 3, 2010

New Theropod Database Update!

This has been a long time coming.  The huge news this time is a brand new section- Ex-Theropod Taxa, which will cover all taxa ever thought to be theropods. I'm excited about writing this section because I'm not familiar with most of the taxa until I research them, so I'm learning quite a bit. Far too often, ex-dinosaurs get ignored by both dinosaur experts and whatever group they end up belonging to, leading to only a superficial knowledge of what they are. Ex-theropods which I've previously covered on my blog include Priscavolucris, the Kota bird, Bathygnathus, "Yezosaurus", Rachitrema, Actiosaurus, Patricosaurus, Megalancosaurus, Longisquama, Gwyneddosaurus, Ankistrodon, "Likhoelesaurus", Tanystrosuchus and Arctosaurus. Ex-theropods which have significant entries that haven't made it to the blog includde Coelurosauravus, Spinosuchus, Pneumatoarthrus, Tanystropheus, Teratosaurus? bengalensis, Avalonianus, "Cinizasaurus", "Cryptoraptor", Sinosaurus? "shawanensis", Trialestes, Sinocoelurus, Teyuwasu, Eucoelophysis, Apatodon, "Troodon" isfarensis, Gresslyosaurus, Eucnemesaurus and Gryponyx. I also moved herrerasaurids and other controversial basal saurischians to the ex-theropod page, since it more accurately reflects their position. Among these, Sanjuansaurus was added, and Eoraptor and Herrerasaurus both got huge makeovers.

Okay, but what about theropods themselves? Tawa was finally added, as was Kayentavenator, and the Coelophysis entry was updated. "Coelurosaurus", "Carnosaurus", Concavenator, Zuolong, Machairasaurus, Balaur, Bauxitornis, "Confuciusornis" jianchengensis, Intiornis, Palintropus, Anatalavis, Neogaeornis, Polarornis and Cimolopteryx were added. Rahiolisaurus was updated, and Cathayornis was separated from Sinornis after O'Connor and Dyke (2010).

Finally, I added the evaluations of Perez-Moreno et al.'s (1994) analysis of Pelecanimimus' position, Chiappe and Calvo's (1994) major analysis of bird phylogeny and the massive effort that is Holtz's (1994) famed theropod analysis.

What's in store for the future? Adding Ezcurra's (2010) and Nesbitt et al.'s (2010) data to the saurischian supermatrix which will let me add the character evidence for conflicting hypotheses to the entries of herrerasaurids, Eoraptor, Chindesaurus, Guaibasaurus, etc., evaluating some more modern analyses like Smith et al. (2007) or the TWG matrix, adding more archosaurian ex-theropods, making the cladogram reflect the data better when competing topologies are poorly distinguished by parsimony, and fleshing out entries to include more commentary and characters (both for diagnoses and for alternative placements for taxa).

Thursday, December 2, 2010

Zuolong, a new basal coelurosaur from the Shishugou Formation

No, this isn't the 'important post' alluded to last time, but I had to take advantage of the opportunity to post on a new theropod so soon after it was announced (and before Andrea got to it!).  Today we see the publication of Zuolong, or "animal dragon", er... actually it's named after General Zuo Zongtang.  Avid theropod fans will know this as the basal coelurosaur skull shown and announced by Clark et al. at SVP 2002.  The description is nicely detailed and illustrated, and I look forward to seeing where it ends up in Cau's megamatrix.  The phylogenetic analysis is mostly in the supplementary data, so I can't evaluate it, though given Choiniere's past published analyses I'm crossing my fingers that taxa are completely coded this time around.  On the positive side, the authors do discuss in detail the alternative placements for basal coelurosaurs which cause the illustrated polytomy, and used a reduced consensus method to prune taxa from the tree a posteriori.  Nqwebasaurus was excluded since a redescription is in preparation for the Journal of African Earth Sciences, though I note the Limusaurus analysis found it to be a basal ornithomimosaur.  Tugulusaurus was sometimes not a coelurosaur, a result my supermatrix has also found.  Bagaraatan was either a tyrannosauroid or an ornithomimosaur.  Aniksosaurus was a basal compsognathid.  Proceratosaurus could be either a tyrannosauroid, compsognathid or ornithomimosaur, highlighting the caution I've been urging in assigning these small taxa to Tyrannosauroidea.  Of course I have no idea what the quality of the matrix is, so I don't know how important those results are.  On the negative side, Choiniere is again redefining taxa with "a modified version of the definition of Coelurosauria from Holtz et al. (2004) as all theropods more closely related to birds than to Sinraptor dongi."  There's no reason to change the standard Allosaurus external specifier that everyone's used up to this point, not to mention the error everyone else makes in using birds to define Coelurosauria contra Recommendation 11A.  In any case, I'm glad to see this description published, and look forward to the upcoming osteologies of Guanlong and Haplocheirus.

Much of the holotype of Zuolong salleei (IVPP V15912).  Note the sacrum plus proximal caudals were shifted in front of the pelvis for viewing purposes, and some elements like the scapula and several partial vertebrae are not shown.  Scale = 1 m. (after Choiniere et al., 2010)

Zuolong Choiniere, Clark, Forster and Xu, 2010
Z. salleei Choiniere, Clark, Forster and Xu, 2010
Early Oxfordian, Late Jurassic
Shishugou Formation, Xinjiang, China

Holotype- (IVPP V15912) (~3.1 m; ~35 kg; subadult) incomplete skull, premaxillary tooth, angular, two lateral teeth, partial axial neural arch, incomplete third cervical vertebra, incomplete fourth cervical vertebra, incomplete fifth cervical vertebra, incomplete eighth cervical vertebra, incomplete ninth cervical vertebra, partial tenth cervical neural arch, two dorsal centra, two fragmentary dorsal centra, incomplete sacrum, first caudal neural arch, second caudal neural arch, third caudal centrum, incomplete fourth caudal vertebra, three incomplete mid caudal vertebrae, two mid caudal centra, mid caudal neural arch, incomplete scapula, incomplete humerus, radius (137 mm), incomplete ulna, distal phalanx I-1, incomplete manual ungual I, partial ilium, incomplete pubes, femora (one distal; 336 mm), partial tibia, proximal fibula, partial phalanx I-1, pedal ungual I, metatarsal II (191.9 mm), phalanx II-1, metatarsal III (224.3 mm), partial metatarsal IV (~201.7 mm)

Diagnosis- (after Choiniere et al., 2010) large, slit-like quadrate foramen inclined medially at approximately 45 degrees with associated deep fossa on the quadrate; sacral centrum 5 with an obliquely oriented posterior articular surface that is angled anterodorsally; fovea capitis very large, occupying almost the entire posterodorsal surface of the femoral head; distal condyle of metatarsal III large relative to that of other metatarsals and bearing an anteromedially projecting flange on its anteromedial margin.

Skull elements of Zuolong salleei, scaled from figures in Choiniere et al. (2010). Note the squamosal's scale bar in figure 4 is assumed to be 1 cm instead of 3 cm as listed.  The mass above the orbit is the frontal and parietal in dorsal view.

Comments- This specimen was discovered in 2001 and announced in an abstract by Clark et al. (2002) as a basal coelurosaur. It was later described in more detail in an abstract by Choiniere et al. (2008), who used a version of the TWG matrix and found it to be one of the most basal coelurosaurs, sister to Tugulusaurus. Choiniere et al. (2010) named and described the taxon in depth, finding it either as a non-tyrannoraptoran coelurosaur in a trichotomy with Tugulusaurus or as a non-maniraptoriform tyrannoraptoran more derived than tyrannosauroids.

References- Clark, Xu, Forster, Wang and Andres, 2002. New small dinosaurs from the Upper Jurassic Shishugou Formation at Wucaiwan, Xinjiang, China. Journal of Vertebrate Paleontology. 22(3), 44A.

Choiniere, Clark, Xu and Forster, 2008. A new basal coelurosaur from the upper Shishugou Formation (Xinjiang, People's Republic of China). Journal of Vertebrate Paleontology. 28(3), 63A.

Choiniere, Clark, Forster and Xu, 2010. A basal coelurosaur (Dinosauria: Theropoda) from the Late Jurassic (Oxfordian) of the Shishugou Formation in Wucaiwan, People's Republic of China. Journal of Vertebrate Paleontology. 30(6), 1773-1796.

Wednesday, December 1, 2010

"Likhoelesaurus" the mysterious African nomen nudum

Quick update before an important post...

"Likhoelesaurus" Ellenberger, 1970
"L. ingens" Ellenberger, 1970
= "Likhoelesaurus ferox" Ellenberger, 1972
Norian, Late Triassic
Lower Elliot Formation, Lesotho
- five teeth (70 mm)

Comments- Ellenberger and Ginsberg (1966) mentioned carnivorous dinosaur teeth from the Lower Elliot Formation, which were later called "Likhoelesaurus ingens" by Ellenberger (1970) and referred to Ornithosuchidae. These were not described properly though, making the name a nomen nudum. Ellenberger (1972) referred to "Likhoelesaurus ferox" as a "giant carnosaur" from zone A/5 of his lower red beds, illustrating five associated recurved teeth in a plate. This was another nomen nudum, with no explanation of the different species name (it may involve Basutodon ferox, but even if "Likhoelesaurus" were officially named, Basutodon would have priority). Kitching and Raath (1984) suggested it may be a junior synonym of Basutodon ferox. It was listed as a teratosaurid theropod by Chure and McIntosh (1989) and a melanorosaurid by Olshevsky (1991). Glut (1997) listed it as ?Theropoda incertae sedis, listed "?bones" among the remains and stated the teeth were 70 mm long. Knoll (2004) discusses the material under Rauisuchia, but notes it could be theropod as well.

Presumably the type material of "Likhoelesaurus ingens", from Ellenberger (1972).

With no published description, and only one undetailed photograph, the phylogenetic position of "Likhoelesaurus" remains uncertain. While their recurved morphology excludes referral to Melanorosauridae or any other sauropodomorph clade, differences between the teeth of carnivorous dinosaurs, crutotarsans (including ornithosuchids and teratosaurs) and other carnivorous archosauriforms have yet to be studied. Indeed, they are only assumed to be archosauriform here due to past identifications, since the presence of serrations has not been confirmed.  Synonymy with Basutodon is possible, but no shared derived characters have been suggested, Basutodon itself is probably undiagnostic and multiple archosauriform taxa are known from other Late Triassic localities.

References- Ellenberger and Ginsberg, 1966. Le gisement de Dinosauriens triasiques de Maphutseng (Basutoland) et l'origine des Sauropodes [The Triassic dinosaur locality of Maphutseng (Basutoland) and the origin of sauropods]. Comptes Rendus de l'Académie des Sciences à Paris, Série D. 262, 444-447.

Ellenberger, 1970. Les niveaux paléontologiques de première apparition des mammifères primoridaux en Afrique du Sud et leur ichnologie. Establissement de zones stratigraphiques detaillees dans le Stormberg du Lesotho (Afrique du Sud) (Trias Supérieur à Jurassique) [The paleontological levels of the first appearance of primordial mammals in southern Africa and their ichnology. Establishment of detailed stratigraphic zones in the Stormberg of Lesotho (southern Africa) (Upper Triassic to Jurassic). in Haughton (ed.). Second Symposium on Gondwana Stratigraphy and Paleontology, International Union of Geological Sciences. Council for Scientific and Industrial Research, Pretoria. 343-370.

Ellenberger, 1972. Contribution à la classification des Pistes de Vertébrés du Trias: Les types du Stormberg d'Afrique du Sud (I). Palaeovertebrata. 104, 152 pp.

Kitching and Raath, 1984. Fossils from the Elliot and Clarens Formations (Karoo Sequence) of the Northeastern Cape, Orange Free State and Lesotho, and a suggested biozonation based on tetrapods. Palaeontologia Africana. 25, 111-125.

Chure and McIntosh, 1989. A Bibliography of the Dinosauria (Exclusive of the Aves) 1677-1986. Museum of Western Colorado Paleontology Series #1. 226 pp.

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

Glut, 1997. Dinosaurs - The Encyclopedia. McFarland Press, Jefferson, NC. 1076 pp.

Knoll, 2004. Review of the tetrapod fauna of the "Lower Stormberg Group" of the main Karoo Basin (southern Africa): Implication for the age of the Lower Elliot Formation. Bulletin de la Societe Geologique de France. 175(1), 73-83.

Tuesday, November 23, 2010

Recommended definitions for theropod clades Part 1

January 1, 201n is fast approaching along with what will no doubt be a rush to define clades.  The major clades' definitions are already written up for Phylonyms, but there's still hope we can salvage ideal definitions for smaller groups.  It's my hope that authors will use this as a reference to see why certain definitions should and shouldn't be used before they try to register them.

First, some basic rules.
1. If the clade is named after a genus, use the type species of that genus as an internal specifier.  It doesn't matter if it's indeterminate, poorly known or not well nested because it has to belong to the clade in question or else the clade would need a different name.  For example, Sereno defined Alvarezsauridae using Shuvuuia, but if the more poorly known and more basal Alvarezsaurus didn't belong, we couldn't keep calling Shuvuuia's clade Alvarezsauridae anyway.
2. If the clade isn't named after a genus, use the type species of one of the genera originally included by the clade's author as an internal specifier.
3. Whenever possible, use external specifiers that were thought by the clade's author to not belong to it.
4. Strive to make the definition congruent with all suggested topologies, not just your own.  It's naive to think we have the right phylogeny today.
5. If a more than one definition follows the above rules, use the one proposed first.

Herrerasauria Galton, 1985
Definition- (Herrerasaurus ischigualastensis <- Liliensternus liliensterni, Plateosaurus engelhardti) (modified from Langer, 2004)
Comments- No issues, I just added the type species.

Herrerasauridae Benedetto, 1973
Definition- (Herrerasaurus ischigualastensis + Staurikosaurus pricei) (modified from Novas, 1992)
Comments- Sereno (1998) proposed a stem-based definition, but Novas' was first, which follows Galton's (1985) earlier taxonomy of having non-herrerasaurid herrerasaurs.

Avepoda Paul, 2002
Definition- (metatarsal I does not contact distal tarsals homologous with Passer domesticus) (modified from Paul, 2002)
Comments- Paul used "Neotheropoda", so Passer domesticus is used since of the two internal neotheropod specifiers, only it has a preserved first metatarsal.

Averostra Paul, 2002
Definition- (promaxillary fenestra homologous with Dromaeosaurus albertensis) (modified from Paul, 2002)
Comments- Paul's definition used the less specific Dromaeosauridae and did not indicate which accessory maxillary opening should be used.  The promaxillary fenestra is specified, since basal averostrans of Paul only have it, and not a maxillary fenestra.  Ezcurra and Cuny's (2007) node-based definition is not used because it postdates Paul's for a taxon Paul created, and is a junior synonym of Neotheropoda.

Coelophysoidea Nopcsa, 1928 sensu Holtz, 1994
Definition- (Coelophysis bauri <- Ceratosaurus nasicornis, Passer domesticus) (first order revision of Padian et al., 1999)
Comments- Sereno's (1998) definition used Carnotaurus, but abelisaurids have been sometimes seen as carnosaurs (Kurzanov, 1989) and Ceratosaurus has been consistantly used in phylogenies due to its early discovery.  Sereno (online) suggested adding Passer, which is good for phylogenies like Raath's (1984) and early ones where birds derived from Coelurosauria sensu Huene (e.g. Barsbold, 1984).  Is it too much to ask for Podokesauroidea being (Podokesaurus holyokensis <- Ceratosaurus nasicornis, Passer domesticus)?

Dilophosauridae Madsen and Welles, 2000
Definition- (Dilophosaurus wetherilli <- Coelophysis bauri, Allosaurus fragilis) (new)
Comments- This hasn't been defined yet, but besides the obvious Coelophysis, I think Allosaurus is better than Passer since it covers older topologies where Dilophosaurus was carnosaurian AND newer ones where we just need a tetanurine specifier.

Procompsognathidae/inae- Given a definition by Sereno (1998), this seems unwise until more than his studies indicate a need for such a clade, and until Procompsognathus' position even as a theropod is more established.

Coelophysidae Nopcsa, 1928 sensu Welles, 1984
Definition- (Coelophysis bauri + Megapnosaurus rhodesiensis + "Megapnosaurus" kayentakatae) (Holtz, 1994)
Comments- Though Paul (1988) and Novas (1991, 1992) included Dilophosaurus, Welles did not and Coelophysoidea is well established as that larger clade.  Sereno (1998) used Procompsognathus as an internal specifier, but it's been placed outside Coelophysoidea by some authors (Gauthier, 1984; Paul, 1984, 1988; Allen, 2004) so this is not recommended.  Tykoski and Rowe (2004) left out kayentakatae, but Holtz's including it lets us use Coelophysinae for that smaller clade.
Incidentally, if we were allowed to start over, I would use Podokesauridae and define it as (Podokesaurus holyokensis <- Liliensternus liliensterni, Coelurus fragilis, Compsognathus longipes) for this family.  This covers Coelophysis as well, since Podokesaurus shares longer dorsal centra with it than Liliensternus shows.

Segisaurinae Camp, 1936 sensu Kalandadze and Rautian, 1991
Definition- (Segisaurus halli <- Coelophysis bauri) (new)
Comments- Since Segisaurus is always outside (Coelophysis+Megapnosaurus) in phylogenies, this gives some structure to coelophysid relationships and is equivalent to Sereno's Procompsognathinae but uses a more stable genus.

Coelophysinae Nopcsa, 1928
Definition- (Coelophysis bauri <- Segisaurus halli) (new)
Comments- Sereno (1998) used Procompsognathus as the internal specifier as he had it in a clade with Segisaurus outside Coelophysinae.  Thus this definition retains his concept.  None of the taxa used by Nopcsa as non-coelophysine podokesaurids are useful today (Podokesaurus, Procerosaurus, Saltopus, Tanystropheus), and he only included Coelophysis in the subfamily.

Neotheropoda Bakker, 1986
Definition- (Ceratosaurus nasicornis + Passer domesticus) (modified from Padian et al., 1999)
Comments- Sereno (1998) used Coelophysis as an internal specifier, but podokesaurids were specifically excluded by Bakker.  I considered also using Allosaurus, but Ceratosaurus has never been closer to birds than Allosaurus in any topology with coelophysoids outside a Ceratosaurus+Allosaurus clade, and all the authors to use Neotheropoda have theropod birds.  Although the clade now fails under a BAND phylogeny, using Allosaurus instead of Passer would make it fail under the more likely phylogeny where Ceratosaurus is a carnosaur.

Ceratosauria Marsh, 1884
Definition- (Ceratosaurus nasicornis <- Allosaurus fragilis, Passer domesticus) (first order revision of Rowe, 1989)
Comments- Rowe and Gauthier's (1990) definition was node-based and used every ceratosaur they recognized, which is less stable especially since most are coelophysoids.  Sereno's (1998) used Coelophysis, which doesn't work in many phylogenies since it's outside Ceratosaurus+tetanurines.  I think Allosaurus would be a good taxon to add, to account for the many early phylogenies where Ceratosaurus was a carnosaur (e.g. Bonaparte et al., 1990, Currie, 1995) and those where birds aren't dinosaurs.  It also makes sense as a distinctly non-ceratosaurian theropod of both Marsh and Gauthier. 

Neoceratosauria Novas, 1991
Definition- (Ceratosaurus nasicornis + Abelisaurus comahuensis) (modified from Holtz, 1994)
Comments- Padian et al. (1999) used a stem away from Coelophysis, but in most modern topologies that would include tetanurines as well.  There's controversy over using this compared to Ceratosauroidea Bonaparte et al., 1990.  Neoceratosauria is used far more often, was named unofficially before Ceratosauroidea (in Novas' 1989 thesis) and has been given a more useful definition (Ceratosauroidea's is Ceratosaurus<-Coelophysis).

Ceratosauridae Marsh, 1884
Definition- (Ceratosaurus nasicornis <- Abelisaurus comahuensis, Allosaurus fragilis) (first order revision of Rauhut, 2004)
Comments- Allosaurus is added as an external specifier to cover topologies where Ceratosaurus is closer to Tetanurae than abelisaurids (e.g. Rauhut, 1998).

Abelisauroidea Bonaparte and Novas, 1985 sensu Bonaparte, 1991
Definition- (Abelisaurus comahuensis <- Ceratosaurus nasicornis, Allosaurus fragilis) (first order revision of Holtz, 1994)
Comments- Allosaurus is added as an external specifier for topologies where abelisaurids are tetanurines (e.g. Kurzanov, 1989; Forster, 1999).  Wilson et al. (2003) used a stem-based definition which is covered by Abelisauria.

Abelisauria Novas, 1992
Definition- (Abelisaurus comahuensis + Noasaurus leali) (modified from Novas, 1997)
Comments- Both Abelisauroidea and Abelisauria were created for the same purpose- to separate abelisaurids and noasaurids from ceratosaurids.  I suppose ideally, I'd switch their definitions since -ia suggests a more inclusive clade than -oidea.

Noasauridae Bonaparte and Powell, 1980
Definition- (Noasaurus leali <- Carnotaurus sastrei, Compsognathus longipes) (first order revision of Wilson et al., 2003)
Comments- Compsognathus is added to cover the traditional placement in Coelurosauria (Bonaparte and Powell, 1980), as a substitute for Sereno's (online) suggestion of Passer.

Abelisauridae Bonaparte and Novas, 1985
Definition- (Abelisaurus comahuensis <- Noasaurus leali, Ceratosaurus nasicornis, Elaphrosaurus bambergi, Allosaurus fragilis) (new)
Comments- Most definitions have used Carnotaurus as the internal specifier, which is wrong since it isn't the eponymous genus.  The other two are node-based using taxa with uncertain placements, while the above definition is stable and covers all proposed topologies.

Abelisaurinae Bonaparte and Novas, 1985 sensu Paul, 1988
Definition- (Abelisaurus comahuensis <- Carnotaurus sastrei) (modified from Sereno, 1998)

Carnotaurini- I would leave this undefined, since Coria et al.'s original definition could easily be more inclusive than Carnotaurinae, and having Carnotaurus and Aucasaurus as sister taxa isn't supported by recent analyses. 

Carnotaurinae Sereno, 1998
Definition- (Carnotaurus sastrei <- Abelisaurus comahuensis) (Sereno et al., 2004; modified from Sereno, 1998)

Brachyrostra Canale, Scanferla, Agnolin and Novas, 2009
Definition- (Carnotaurus sastrei <- Majungasaurus crenatissimus) (Canale, Scanferla, Agnolin and Novas, 2009)

Continued later with basal tetanurines...

Saturday, November 20, 2010

Megalancosaurus is not a theropod or a bird ancestor

 Another quickie from the ex-theropod files. 

Megalancosaurus Calzavara, Muscio and Wild, 1980
M. preonensis Calzavara, Muscio and Wild, 1980
Middle Norian, Late Triassic
Dolomia di Forni Formation, Italy

Holotype- (MFSN 1769) skull (30 mm), mandibles (18 mm), hyoid, several cervical vertebrae (third 7 mm, sixth 9 mm), second dorsal neural spine, fused third and fourth dorsal neural spines, two dorsal ribs, dorsal rib fragments, scapula (23 mm), coracoid fragment, humerus (22 mm), radius (15 mm), ulna (15 mm), intermedium, ulnare, centrale, distal carpal I, distal carpal II, distal carpal III, metacarpal I (1.5 mm), phalanx I-1 (6 mm), partial manual ungual I, metacarpal II (3 mm), incomplete phalanx II-1 (6 mm), metacarpal III (3.5 mm), partial phalanx III-1 (6 mm), manual ungual III (4 mm), metacarpal IV (3 mm), partial phalanx IV-1 (3 mm), phalanx IV-2 (5 mm), manual ungual IV (4.5 mm), metacarpal V (2 mm), partial phalanx V-1 (3 mm), phalanx V-2 (4 mm), manual ungual V (4.5 mm)
Referred- (MFSN 1801) caudal vertebrae 8-38 fused to chevrons (Pinna, 1987)
(MFSN 18443a) caudal vertebrae 13-38 (Renesto, 2000)

Middle Norian, Late Triassic
Zorzino Limestone Formation, Italy

(MBSN 26; paratype of Drepanosaurus unguicaudatus) cervical vertebrae (third 4.5 mm, sixth 6 mm), anterior dorsal vertebrae (second 4 mm), anterior dorsal ribs, posterior dorsal vertebrae fused to dorsal ribs (eighteenth 3 mm), supraneural element, caudal vertebrae fused with chevrons (tenth 5.5 mm), scapulae (21 mm), humerus (18.5 mm), radius, ulna, pelvis, femur (20 mm), tibia (11.5 mm), fibula, pes (Pinna, 1980)
(MPUM 6008; = P 11 24) cervical vertebrae (third 7.5 mm, fifth 9.5 mm, sixth 10 mm), anterior dorsal vertebrae (second 6 mm), anterior dorsal ribs, posterior dorsal vertebrae fused to dorsal ribs, supraneural element, sacral vertebrae, caudal neural spines, scapula (23 mm), coracoids, humerus (22.5 mm), radius (14 mm), ulna (14 mm), proximal carpal, four distal carpals, phalanx I-1 (6 mm), manual ungual I (4 mm), metacarpal II (3 mm), phalanx II-1 (6 mm), manual ungual II (4 mm), metacarpal III (3 mm), phalanx III-1 (6 mm), manual ungual III (4 mm), metacarpal IV (2.5 mm), phalanx IV-1 (3 mm), phalanx IV-2 (5 mm), phalanx V-1 (2.5 mm), phalanx V-2 (4 mm), manual ungual V (3.5 mm), three manual phalanges, two manual unguals, partial pelvis (Renesto, 1994)
(MPUM 8437; = CCSR 63115) posterior skull, incomplete mandible, eight cervical vertebrae (fifth 7 mm, sixth 7.5 mm), five anterior dorsal vertebrae, anterior dorsal ribs, eighteen posterior dorsal vertebrae fused to dorsal ribs, supraneural element, three sacral vertebrae, thirty-nine caudal vertebrae fused to chevrons, partial scapula, partial coracoid, clavicle, distal humerus (~21 mm), radius (11 mm), ulna (12 mm), intermedium, ulnare, two centrales, distal carpal I, distal carpal II, distal carpal III, distal carpal IV, distal carpal V, metacarpal I, phalanx I-1, partial manual ungual I, metacarpal II, incomplete phalanx II-1, incomplete manual ungual II, metacarpal III (4 mm), phalanx III-1 (5 mm), manual ungual III, metacarpal IV, phalanx IV-1, phalanx IV-2, manual ungual IV, metacarpal V, phalanx V-1, incomplete phalanx V-2, manual ungual V, partial pelvis, femora (27 mm), tibiae (17.5 mm), fibulae (16 mm), astragali, calcanea, centrale, distal tarsal I, distal tarsal II, distal tarsal III, distal tarsal IV, metatarsal I, phalanx I-1, pedal ungual I, metatarsal II, phalanx II-1, phalanx II-2, pedal ungual II, metatarsal III (4 mm), phalanx III-1 (3 mm), phalanx III-2, pedal ungual III, metatarsal IV, phalanx IV-1, phalanx IV-2, phalanx V-1, phalanx V-2, pedal ungual (Renesto, 2000)

Late Triassic?

(MCSNB 7833) (Senter, 2004)

Comments- Megalancosaurus preonensis was discovered in 1980 and originally assigned to Pseudosuchia sensu Huene (Calzavara et al., 1980). Although Carroll (1988) also placed it in Thecodontia (in the traditional paraphyletic sense), generally only those workers who reject cladistics and a dinosaurian origin for birds have continued to call Megalancosaurus an archosaur (e.g. Feduccia and Wild, 1993; Feduccia, 1996). This is almost exclusively based on its supposed antorbital fenestra (considered near certainly absent by Renesto and Dalla Vecchia, 2005), and presumably the need to have birds derive from archosaurs. Megalancosaurus is currently placed in the larger clade Simiosauria, which has a highly uncertain placement among eosuchians. Various analyses place them outside Neodiapsida, sister to Euryapsida, in Lepidosauromorpha, as non-thecodont archosauromorphs or as 'protorosaurs', with the latter three possibilities sometimes including a close relationship with pterosaurs. Determining their relationships will require a larger diapsid phylogenetic analysis than those currently published.

Megalancosaurus a theropod? Olshevsky (1991) believed Megalancosaurus to be a basal theropod (or in his taxonomy, a basitheropod theropodomorph), but this was based only on the holotype. Of the theropodomorph characters he lists, carnivorous dentition is primitive for gnathostomes, while new specimens show Megalancosaurus lacks erect limbs and a reduced calcaneum. Of Olshevsky's basitheropod characters, an antorbital fenestra is primitive for archosauriforms and probably lacking in Megalancosaurus, "generally avian appearence of the skull" is vague and unlike basal theropods, relatively large forelimbs are primitive for tetrapods and unlike basal theropods, "clavicles, fused clavicles, or primitive furcula" covers every possibility and Megalancosaurus' are unfused which is primitive for tetrapods, and pentadactyl manus and pes are plesiomorphic for tetrapods and not found in basal theropods. The tarsus is not even incipiently mesotarsal and as noted above the calcaneum is not reduced. Megalancosaurus does share the presence of at least three sacral vertebrae with dinosaurs, but this is present in pterosaurs and some other taxa as well. Furthermore, the more basal Vallesaurus and Drepanosaurus only have two sacrals. While Megalancosaurus and theropods both have manus capable of grasping, in theropods digit I is angled towards II and III due to an asymmetrical metacarpal I articulation and twisted phalanx I-1, whereas in Megalancosaurus half the digits oppose the other half due merely to a lack of articulation between the metacarpals. This suggests the grasping abilities are convergent.  

Megalancosaurus lacks numerous characters expected in a basal theropod, such as subnarial fenestra, external mandibular fenestra, thecodont dentition, more than eight cervicals, cervical epipophyses, vertebral laminae, dicephalous dorsal ribs, reduced manual digits IV and V, perforated acetabulum, dorsally angled preacetabular process, elongate postacetabular process, elongate pubis and ischium, inturned femoral head, anterior and fourth trochanter, mesotarsal ankle, reduced calcaneum, centrale absent, less than three distal tarsals, and reduced pedal digit V. These make it virtually impossible to assign Megalancosaurus to Dinosauria, let alone Theropoda.

Megalancosaurus a bird ancestor? Feduccia and Wild (1993) first suggested Megalancosaurus was more closely related to birds than theropods were, though the absence of other taxa in their cladogram leaves one uncertain exactly where in Archosauria they place the the Megalancosaurus+bird clade. The expanded braincase is also present in pterosaurs and coelurosaurs. Large orbits are found in those two groups as well, and many other small tetrapods. A pointed snout is also present in many maniraptoriforms, pterosaurs, most 'protorosaurs', choristoderes, thalattosaurs, and some basal lepidosauromorphs. The "large, oval preorbital fenestra" is actually the external naris. The reduced premaxillary dentition is not present in basal birds, though the authors state it "may be important, because when modern birds loose their teeth they loose the maxilla that houses them, and in the Cretaceous toothed birds, the teeth are borne only on the maxilla." Even ignoring the fact Aves does retain a maxilla, and subsequently discovered birds like omnivoropterygids and longipterygids have toothed premaxillae and toothless maxillae, mere propensity for a group to exhibit a character is not a synapomorphy. The dentary is said to be birdlike, but this is too vague to evaluate. The foramen magnum is claimed to be posteroventrally oriented, but this is based solely on the angle of the quadrate and ventral squamosal process. The latter is also true in Icarosaurus, the basal squamate Tamaulipasaurus, the basal choristodere Lazarussuchus, Cosesaurus and pterosaurs. Feduccia and Wild state "the six to seven elongate cervical vertebrae create a highly movable birdlike neck." The high mobility is caused by heterocoelous centra, which are similar to ornithuromorphs but not basal birds. Elongate cervical centra are present in coelurosaurs, 'protorosaurs' and other taxa, while birds have at least nine cervicals. Though the authors claim the "anterior limbs, without manus, are proportionately similar to those of modern birds and Archaeopteryx; and dissimilar to theropods," the radiohumeral ratio of 68% is shorter than most maniraptorans (even taxa known in 1993, e.g. Oviraptor 87%, Deinonychus 76%) and Archaeopteryx (84-96%), while modern birds usually have ratios of more than 100%. The large manual ungual flexor tubercles are said to be birdlike, but these are absent in the more basal Hypuronector, and also found in most theropods and pterosaurs. Contra Feduccia and Wild, the forelimbs minus manus are not longer than the hindlimbs minus pes, being 72% as long instead. Finally, the straplike scapula is indeed superficially like Aves in being extrenmely slender, bowed and having a tapered distal end. Yet basal birds lack these features, and only have scapulae as slender as pterosaurs and most theropods.

Feduccia later (1996) refers to Megalancosaurus' "tiny isodont teeth set in sockets", but they are actually subthecodont as in most basal diapsids, while isodonty is also plesiomorphic.

After the mid-1990s, Feduccia and other Birds Are Not Dinosaurs supporters seem to have reduced their emphasis on Megalancosaurus' relationship with birds. Geist and Feduccia (2000) repeat the 1993 observations, but then state "though probably not the avian ancestor, Megalancosaurus represents a chronologically and biophysically plausible model for a gliding stage through which birds must have passed." Martin (2004) incorrectly stated Megalancosaurus has a furcula, but did not explicitly link it to bird origins.

Besides those characters noted above that exclude Megalancosaurus from Theropoda, it is less similar to basal birds than even basal coelurosaurs are in many other ways. These include the absence of pleurocoels, less than five sacral vertebrae, absence of a transition point in the tail, unfused clavicles, small distal carpal I, metacarpal III longer than II, presence of manual digits IV and V, absent pubic boot, absent obturator process, obturator foramen in pubis, astragalus without tall ascending process, robust metatarsus, metatarsal I reaching tarsus, and phalanx V-1 present.

References- Calzavara, Muscio and Wild, 1980. Megalancosaurus preonensis, n. g., n. sp., a new reptile from the Norian of Friuli. Gortania. 2, 49-63.

Pinna, 1980. Drepanosaurus unguicaudatus, nuovo genere e nuova specie di lepidosauro del Trias alpino. Atti della Società Italiana di Scienze Naturali - Museo civico di Storia Naturale di Milano. 121, 181-192.

Pinna, 1987. Un nuovo esemplare giovanile di Drepanosaurus unguicaudatus del Norico di Val Preone (Udine) [A new juvenile specimen of Drepanosaurus unguicaudatus from the Norian of the Preone Valley, Udine]. Atti della Società Italiana di Scienze Naturali - Museo civico di Storia Naturale di Milano. 128, 80-84.

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

Feduccia and Wild, 1993. Birdlike characters in the Triassic archosaur Megalancosaurus. Naturwissenschaften. 80, 564-566.

Renesto, 1994. Megalancosaurus, a possibly arboreal archosauromorph (Reptilia) from the Upper Triassic of northern Italy. Journal of Vertebrate Paleontology. 14(1), 38-52.

Feduccia, 1996. The Origin and Evolution of Birds. Yale University Press. 420 pp. 

Ruben, 1998. Gliding adaptations in the Triassic archosaur Megalancosaurus. Journal of Vertebrate Paleontology. 18(3), 73A.

Geist and Feduccia, 2000. Gravity-defying behaviors: Identifying models for protoaves. American Zoologist. 40, 664-675.

Renesto, 2000. Bird-like head on a chameleon body: New specimens of the enigmatic diapsid reptile Megalancosaurus from the Late Triassic of northern Italy. Rivista Italiana di Paleontologia e Stratigrafia. 106(2), 157-180.

Martin, 2004. A basal archosaurian origin for birds. Acta Zoologica Sinica. 50(6), 978-990.

Senter, 2004. Phylogeny of the Drepanosauridae (Reptilia: Diapsida). Journal of Systematic Palaeontology. 2, 257-268.

Renesto and Dalla Vecchia, 2005. The skull and lower jaw of the holotype of Megalancosaurus preonensis (Diapsida, Drepanosauridae) from the Upper Triassic of Northern Italy. Rivista Italiana di Paleontologia e Stratigrafia. 111(2), 247-257.

Renesto, Spielmann, Lucas and Spagnoli, 2010. The taxonomy and paleobiology of the Late Triassic (Carnian-Norian: Adamanian-Apachean) drepanosaurs (Diapsida: Archosauromorpha: Drepanosauromorpha). New Mexico Museum of Natural History and Science Bulletin. 46, 1-81.

Friday, November 19, 2010

Theropoda's new entry

To celebrate the new look of the Theropod Database Blog, here's the new entry for Theropoda for the upcoming update of the Database.  It excludes the section discussing Gonipoda, Harpagosauria and Carnosauriformes, which was featured in a prior post. Unfortunately, my favored phylogenetic definition won't be the one set by the Phylocode, though theirs is better than the other three listed here at least.

Theropoda Marsh, 1881
Definition- (Allosaurus fragilis <- Morosaurus impar) (modified from Kischlat, 2000)
Other definitions- (Passer domesticus <- Saltasaurus loricatus) (Sereno, 2004; modified from Sereno, 1998; modified from Gauthier, 1986)
(Passer domesticus <- Cetiosaurus oxoniensis) (Holtz and Osmolska, 2004; modified from Gauthier, 1986)
(Allosaurus fragilis <- Plateosaurus engelhardti) (modified from Clarke et al., 2004)

= Goniopoda Cope, 1866
= Carnosauriformes Cooper, 1985
= Theropoda sensu Sereno, 1998
Definition- (Passer domesticus <- Saltasaurus loricatus) (modified)
= Theropoda sensu Clarke, Gauthier, de Queiroz, Joyce, Parham and Rowe, 2004
Definition- (Allosaurus fragilis <- Plateosaurus engelhardti)
= Theropoda sensu Holtz and Osmolska, 2004
Definition- (Passer domesticus <- Cetiosaurus oxoniensis) (modified)

Diagnosis- [upcoming]
Other diagnoses- Marsh's (1881) original diagnosis consisted largely of plesiomorphies- carnivorous; limb bones hollow; digits with prehensile claws; digitigrade pes. The distal pubes are only fused in adult neotheropods. "Vertebrae more or less cavernous" refers to the extremely constricted dorsal centra of Allosaurus, which aren't present in most theropods. "Post-pubis present" probably refers to Allosaurus' elongate pubic boot, which is only present in some avetheropods.
Marsh (1884) added more plesiomorphies- premaxilla toothed; external nares placed anteriorly; large antorbital fossa; forelimbs short; propubic pelvis.
[more will be listed of course, though this will be a long process since so many authors have diagnosed Theropoda]

Comments- Marsh (1881) named Theropoda as a dinosaur suborder containing only the Allosauridae, in which he placed Allosaurus, Creosaurus and Labrosaurus (both of the latter now recognized as synonyms of Allosaurus). By 1884, Marsh had raised Theropoda to an order and expanded it to include all carnivorous dinosaurs, as well as what are today recognized as basal sauropodomorphs (often mixed with cranial elements of canivorous crurotarsans). This was the standard for many decades, as seen in Romer's (1956) classic work, in which theropods consist of coelurosaurs, carnosaurs and prosauropods. The monophyly of theropods was questioned by Huene (1914), who placed most of the larger taxa such as Allosaurus and Megalosaurus in Sauropodomorpha (his Pachypodosauria) while the smaller taxa (which he named Coelurosauria) had branched off earlier. In the 1960's, workers began to recognize the monophyly of coelurosaurs and carnosaurs to the exclusion of basal sauropodomorphs (e.g. Colbert, 1964). Paul (1984) was the first author to use a theropod phylogeny similar to todays, with deinonychosaurs (albeit paraphyletic), tyrannosaurids, allosaurids, Eustreptospondylus, Ceratosaurus and coelophysoids forming successively more distant sister taxa to birds. Gauthier's (1984) thesis also had a modern topology, with deinonychosaurs, ornithomimids, carnosaurs and ceratosaurs (the latter two improbably inclusive, containing tyrannosaurids and coelophysoids respectively) successively further from birds, and is the basis of our current nomenclature for major clades.

Theropoda defined- Gauthier (1986) was the first to phylogenetically define Theropoda, as "birds and all saurischians that are closer to birds than they are to sauropodomorphs." Variations on this definition have been most common, with Sereno (1998) using Neornithes and Saltasaurus, specified by Sereno (2004) as Passer domesticus and Saltasaurus loricatus. Holtz and Osmolska (2004) chose Cetiosaurus oxoniensis as the sauropodomorph specifier instead. However, this class of definition violates Phylocode Recommendation 11A- "Definitions of converted clade names should be stated in a way that attempts to capture the spirit of traditional use to the degree that it is consistent with the contemporary concept of monophyly." While birds are currently thought to be theropods, this was not the consensus until over a century after Theropoda was named. Similarly, Clarke et al.'s (2004) definition using Plateosaurus engelhardti as an external specifier is problematic since basal sauropodomorphs were often included in Theropoda until the 1960s. Kischlat (2000) suggested all taxa closer to Allosaurus than to Morosaurus, which is valid in using taxa Marsh (1881) and everyone since have recognized as being theropod and non-theropod. This definition is modified here by including the types species of each genus.

Ex-theropods- Numerous taxa (at least 130) have been incorrectly placed in Theropoda in the past, including ornithosuchids, poposaurids, most basal avemetatarsalians and basal sauropodomorphs, and many Triassic archosauriforms known only from teeth. This site will have an entire section devoted to ex-theropods, so they are not discussed further here.

References- Cope, 1866. [On the anomalous relations existing between the tibia and fibula in certain of the Dinosauria]. Proceedings of the Academy of Natural Sciences of Philadelphia. 18, 316-317.

Marsh, 1881. Principal characters of American Jurassic dinosaurs. Part V. American Journal of Science. 21, 417-423.

Marsh, 1884. Principal characters of American Jurassic dinosaurs. Part VIII. The order Theropoda. American Journal of Science. 27, 329-340.

Huene, 1914. Das natürliche System der Saurischia [The systematics of the Saurischia]. Centralblatt für Mineralogie, Geologie und Paläontologie. 1914, 154-158.

Romer, 1956. Osteology of the Reptiles. University of Chicago Press. 772 pp.

Colbert, 1964. Relationships of the saurischian dinosaurs. American Museum Novitates. 2181, 1-24.

Gauthier, 1984. A cladistic analysis of the higher systematic categories of the Diapsida. PhD thesis. University of California, Berkeley. 564 pp.

Paul, 1984. The archosaurs: A phylogenetic study. Third Symposium on Mesozoic Terrestrial Ecosystems, Short Papers. 175-180.

Cooper, 1985. A revision of the ornithischian dinosaur Kangnasaurus coetzeei Haughton, with a classification of the Ornithischia. Annals of the South African Museum. 95(8), 281-317.

Gauthier, 1986. Saurischian monophyly and the origin of birds. Memoirs of the Californian Academy of Sciences. 8, 1-55.

Sereno, 1998. A rationale for phylogenetic definitions, with application to the higher-level taxonomy of Dinosauria. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen. 210, 41-83.

Kischlat, 2000. Tecodoncios: A aurora dos Arcosaurios no Triassico. in Holz and De Rose (eds.). Paleontologia do Rio Grande do Sul. 273-316.

Clarke, Gauthier, de Queiroz, Joyce, Parham and Rowe, 2004. A phylogenetic nomenclature for the major clades of Amniota Haeckel 1866, with emphasis on Aves Linnaeus 1758. First International Phylogenetic Nomenclature Meeting, Abstracts. 30.

Holtz and Osmólska, 2004. Saurischia. in Weishampel, Dodson and Osmólska (eds.). The Dinosauria. 2nd ed. University of California Press, Berkeley. 21-24.

Sereno, 2004. Phylogenetic nomenclature for stem crocodilians and birds, exclusive of Pterosauria. First International Phylogenetic Nomenclature Meeting, Abstracts. 26.

Thursday, November 18, 2010

All New Design, Same Great Theropod Taste

Finally customized the design to have wider posts, so that my paragraphs appear more manageable.  Also changed the color scheme and added a better background with my drawings.  First person to guess all the illustrated taxa wins... er... five Theropod Database Points.

Wednesday, November 17, 2010

The two undescribed Ischigualasto basal saurischians/theropods

There are two undescribed potential basal theropods from the Ischigualasto Formation, both currently described largely in abstracts. 

undescribed possible theropod (Sereno, 2007)
Norian, Late Triassic
Valle de la Luna Member of the Ischigualasto Formation, San Juan, Argentina
- (~1.6 m) incomplete skeleton including maxilla, cervical vertebrae, distal caudal vertebrae, carpus, manus, pubis, femur and tibia
partial skeletons
Comments- This taxon has only been described in an abstract by Martinez et al. (2008) so far, though the official description is under review. Sereno (2007) states this is a closely related taxon to Eoraptor lunensis, while Martinez et al. (2008) place it as a basal theropod presumably closer to avepods than Eoraptor and herrerasaurids based on several mentioned characters. Phylogenetically informative characters include- promaxillary fenestra; cervical pleurocoels; distal caudal prezygapophyses ~15% of centrum length; pentadactyl manus; extensor pits on metacarpals; pubis distally tapered; pubis posteriorly curved; anterior fossa above distal condyles on femur; tibia longer than femur. Noted additional differences from Eoraptor include more gracile elements, and slender anterior maxillary teeth which are more than twice as long as the former genus.
References- Sereno, 2007. The phylogenetic relationships of early dinosaurs: A comparative report. Historical Biology. 19(1), 145-155.
Martinez, Sereno and Alcober, 2008. A new basal theropod from the Ischigualasto Formation of San Juan Province, Argentina. in Calvo, Valieri, Porfiri and dos Santos (eds.). Libro de Resumenes, III Congreso Latinoamericano de Paleontologia de Vertebrados. Universidad Nacional del Comahue, Neuquen, Argentina. 153.

undescribed herrerasaurid (Ezcurra and Novas, 2007)
Late Carnian-Early Norian, Late Triassic
Cancha de Bochas Member of the Ischigualasto Formation, San Juan, Argentina
- (MACN-PV 18.649a) (small) vertebrae, distal ulna, carpus, manus, pedal phalanges
Diagnosis- (after Ezcurra and Novas, 2007) manual unguals with a posteriorly bifurcated lateral groove.
(after Ezcurra, 2010) manual phalanx II-1 with conspicuous longitudinal ridge on its proximolateral border.
Comments- This specimen was discovered in the 1960s, but not noted until an abstract by Ezcurra and Novas (2007). That paper and Ezcurra (2010) placed it in Herrerasauridae, the latter using a version of Yates' sauropodomorph analysis. It was a herrerasaur based on- manual phalanx I-1 longer than metacarpal I; strongly curved manual unguals; metacarpals IV-V ventral to the others. While these are shared with Herrerasaurus, the unknown forelimb of Staurikosaurus makes the relationship between these three taxa uncertain. The new taxon will be described in more detail by Ezcurra and Novas (in prep.).
References- Ezcurra and Novas, 2007. New dinosaur remains (Saurischia: Herrerasauridae) from the Ischigualasto Formation (Carnian) of NW Argentina. Ameghiniana. 44, 17R.
Ezcurra and Novas, 2008. A review of the dinosaur diversity of the Ischigualasto Formation (Carnian, NW Argentina): Insights on early dinosaur evolution. in Langer, Bittencourt and Castro (eds.). Boletim de Resumos, VI Simposio Brasileiro de Paleontologia de Vertebrados, Paleontologia, Edicao especial. Universidad de Sao Pablo: Ribeirao Preto. 88-89.
Ezcurra, 2010. A new early dinosaur (Saurischia: Sauropodomorpha) from the Late Triassic of Argentina: A reassessment of dinosaur origin and phylogeny. Journal of Systematic Palaeontology. 8(3), 371-425.
Ezcurra and Novas, in prep.

I can send a copy of any of the references if emailed at .

Tuesday, November 16, 2010

Ankistrodon or Epicampodon, but not Agkistrodon or Ancistrodon ...

... which was renamed Ankistrodus then Grypodon.  Yay for taxonomy.  Today we feature another ex-theropod taxon, from the soon-to-be-uploaded (as in, before 2011) Ex-Theropoda section of my site.

Ankistrodon Huxley, 1865
= Epicampodon Lydekker, 1885
A. indicus Huxley, 1865
= Epicampodon indicus (Huxley, 1865) Lydekker, 1885
= Thecodontosaurus indicus (Huxley, 1865) Huene, 1908
= Chasmatosaurus indicus (Huxley, 1865) Huene, 1942

Early Scythian, Early Triassic
Panchet Formation, India
- (GSI coll.) dentary fragment, two teeth
Referred- ?(GSI coll.) cervical vertebrae, anterior dorsal vertebrae, sacral vertebrae, proximal caudal vertebrae (Huene, 1942)

Holotype of Ankistrodon indicus (GSI coll.) in (A) lateral and (B) posterior views, with (C) a cross section of a tooth.  After Huxley, 1865.

Comments- Huxley named and described the holotype, believing it to be a thecodont most similar to the parasuchian Clepsysaurus based on the presence of only distal serrations. He later (1870) referred Thecodontia to Dinosauria, leading him to refer Ankistrodon to the latter clade. Seeley (1880) mentioned the genus as a dinosaur related to Megalosaurus. He later (1885) created the genus Epicampodon for the taxon, since he incorrectly thought Ankistrodon was preoccupied by the recent viperid genus Agkistrodon Palisot de Beauvois, 1799 (or its own unjustified emmendation Ancistrodon Wagler, 1830; or the pycnodontiform fish Ancistrodon Roemer, 1849, which was renamed Ankistrodus then Grypodon). Seeley (1888) illustrated Epicampodon as an anchisaurid theropod, while Nopcsa (1901) listed it as an anchisaurine megalosaurid. It was listed as a zanclodontid theropod by Zittel (1890) and Huene (1902), who incorrectly believed it to be from the Late Triassic Maleri beds. Huene (1906) stated that the species was probably referrable to Thecodontosaurus, though he did not explicitly list the new combination until 1908. In that work he called it Thecodontosaurus(?) indicus, believing it to be most similar to Paleosaurus (his Thecodontosaurus cylindrodon). Das-Gupta (1931) thought the species was similar to his new theropod Orthogoniosaurus in having only distal serrations and having a straight distal edge (actually caused by apical breakage in indicus), placing both in Anchisauridae within Theropoda.

Huene still referred Epicampodon to Saurischia in 1940, but in 1942 recognized it was a more basal archosauriform and made it a species of Chasmatosaurus. This was followed by Tatarinov (1961), but Charig et al. (1976) correctly noted Ankistrodon has priority over Chasmatosaurus (and its senior synonym Proterosuchus). Charig and Reig (1970) and Reig (1970) considered it an indeterminate proterosuchian. Romer (1972) considered the material to be Proterosuchus without explicitly naming the new combination. Most recently, Charig et al. (1976) considered Ankistrodon a seemingly valid genus of proterosuchid, which was followed by Olshevsky (1991). While the presence of serrations does indicate an archosauriform, the Early Triassic age excludes parasuchians and theropods, and the recurved crowns exclude a relationship to sauropodomorphs like Thecodontosaurus or Anchisaurus, evidence supporting a close relationship with Proterosuchus was perhaps only given by Huene (1942), prior to the discovery of a large amount of 'proterosuchian' diversity. Recent analyses suggest that the traditional Proterosuchidae is a paraphyletic grade of basal archosauriforms, so Ankistrodon is here placed in Archosauriformes until further studies on mandibular and dental variation are performed.

Huxley (1865) also described vertebrae as belonging to Dicynodon orientalis (now Lystrosaurus murrayi), which were recognized by Huene (1942) as being archosauriform and referred to his Chasmatosaurus indicus. As the vertebrae cannot be compared to the type jaw fragment, Charig and Reig (1970) merely called them cf. Chasmatosaurus sp..

References- Huxley, 1865. On a collection of vertebrate fossils from the Panchet Rocks, Ranigunu, Bengal. Memoirs of the Geological Survey of India; Paleontologia Indica, Series IV. Indian Pretertiary Vertebrata. i, 3-24.

Huxley, 1870. Triassic Dinosauria. Nature. 1, 23-24.

Lydekker, 1880. A sketch of the history of the fossil Vertebrata of India. Journal and Proceedings of the Asiatic Society of Bengal. 69(2), 8-40.

Lydekker, 1885. The Reptilia and Amphibia of the Maleria and Denwa Groups. Memoirs of the Geological Survey of India. Palaeontologia Indica, Series IV. Indian Pretertiary Vertebrata. 1(5), 1-38.

Seeley, 1888. Catalogue of the Fossil Reptilia and Amphibia in the British Museum (Natural History), Cromwell Road, S.W., Part 1. Containing the Orders Ornithosauria, Crocodilia, Dinosauria, Squamata, Rhynchocephalia, and Proterosauria. British Museum of Natural History, London. 309 pp.

Zittel, 1890. Handbuch der Palaeontologie. Volume III. Vertebrata (Pisces, Amphibia, Reptilia, Aves). 900 pp.

Nopcsa, 1901. A dinosaurusok atnezete es szarmazasa. Földtani Közlöny. 31, 193-224.

Huene, 1902. Übersicht über die Reptilien der Trias [Review of the Reptilia of the Triassic]. Geologische und Paläontologische Abhandlungen (Neue Serie). Gustav Fischer Verlag, Jena. 6, 1-84.

Huene, 1908. Die Dinosaurier der Europäischen Triasformation mit berücksichtigung der Ausseuropäischen vorkommnisse [The dinosaurs of the European Triassic formations with consideration of occurrences outside Europe]. Geologische und Palaeontologische Abhandlungen. Supplement 1(1), 1-419.

Das-Gupta, 1931. On a new theropod dinosaur (Orthogoniosaurus matleyi, n. gen. et n. sp.) from the Lameta beds of Jubbulpore. Journal and Proceedings of the Asiatic Society of Bengal. 26, 367-369.

Huene, 1940. Die Saurier der Karroo-, Gondwana-, und verwandten Ablagerungen in faunistischer, biologischer und phylogenetischer Hinsicht [Saurians of the Karroo, Gondwana, and other deposits in faunistic, biological, and phylogenetic regard]. Neues Jahrbuch für Mineralogie, Geologie und Paläontologie. 83, 246-347.

Huene, 1942. Die Fauna der Panchet-Schichten in Bengalen [The fauna of the Panchet beds in Bengal]. Zentralblatt für Mineralogie, Geologie und Paläontologie, Abteilung B: Geologie und Paläontologie. 1941(11), 354-360.

Tatarinov, 1961. Pseudosuchians of the USSR. Paleontologicheskii Zhurnal. 1961(1), 117-132.

Charig and Reig, 1970. The classification of the Proterosuchia. Biological Journal of the Linnean Society. 2, 125-171.

Reig, 1970. The Proterosuchia and the early evolution of the archosaurs; an essay about the origin of a major taxon. Bulletin of The Museum of Comparative Zoology. 139, 229-292.

Romer, 1972. The Chaneres (Argentina) Triassic reptile fauna. XVI. Thecodont classification. Breviora. 395, 24 pp.

Charig, Krebs, Sues and Westphal, 1976. Thecodontia. Encyclopedia of Paleoherpetology. 13, 137 pp.

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

Monday, November 15, 2010

Averostra and Avepoda

It's been a while since my last post.  Things have been busy around here with my new computer and the holiday season starting up, butb I'll try to post some entries I recently finished.  Today we look at two of Paul's clades from DoA.

Avepoda Paul, 2002
Definition- (metatarsal I does not contact distal tarsals homologous with Allosaurus fragilis) (modified from Paul, 2002)
= Paleotheropoda Paul, 1988

Comments- This clade was first suggested by Paul (1988) as a more appropriate name for Theropoda (as their feet are birdlike as opposed to beastlike), though he recognized Theropoda could not be renamed. In his later 2002 book, Paul actually proposed Avepoda as a subgroup of Theropoda, for those "that either possessed a foot in which metatarsal I did not contact the distal tarsals, or descended from such theropods, and belonged to a clade which includes Neotheropoda." The definition is here modified by using Allosaurus fragilis as the internal specifier, as that taxon is here used as the internal specifier of Theropoda. Avepoda has almost exclusively been used by Paul, with other authors using Neotheropoda (sensu Sereno) for the group since the two usually have the same known content (though Avepoda is near certainly more inclusive than Neotheropoda sensu Sereno, unless coelophysoids were the first theropods to develop the tridactyl pes). However, Procompsognathus was an avepod possibly outside the Coelophysis+Passer clade in Paul's (1988) phylogeny and Gauthier's (1986) analysis, as was Liliensternus in the latter. More recently, Liliensternus was found to be outside the Coelophysis+Passer clade in Bittencourt Rodrigues' unpublished thesis. Avepoda also has an advantage over Neotheropoda in only having one definition, whereas the latter can also apply to the more exclusive Ceratosaurus+Passer clade. Note it is not the same as Avipoda Novas, 1992, which was proposed for a clade similar in extent to Tetanurae.

Paleotheropoda was proposed as a paraphyletic order of theropods by Paul (1988), including all theropods which were not avetheropods. This consisted of what are generally recognized today as coelophysoids, ceratosaurs and megalosauroids, as well as a few other taxa such as Piatnitzkysaurus and sinraptorids. No other reference used the term due to the general dislike of paraphyletic groups, and in 2002 Paul referred to the same grade as baso-avepods. As Paul's (1988) Theropoda was equivalent to Avepoda, Paleotheropoda is catalogued here as a synonym of that group.

Averostra Paul, 2002
Definition- (promaxillary fenestra homologous with Dromaeosaurus albertensis) (modified from Paul, 2002)
Other definitions- (Ceratosaurus nasicornis + Allosaurus fragilis) (Ezcurra and Cuny, 2007)

Comments- Paul (2002) proposed Averostra for a clade of "avepods that either possessed at least one accessory maxillary opening in the lateral wall of the antorbital fossa that led into a bony mediorostral maxillary sinus, or descended from such avepods, and are members of the clade that includes the Dromaeosauridae." This included taxa generally recognized as ceratosaurs and tetanurines, but excluded coelophysoids. The definition is here modified to use Dromaeosaurus albertensis (as the eponymous species for Dromaeosauridae) and to specify the promaxillary fenestra (as it is the first accessory maxillary opening to evolve, and the only one present in taxa Paul considers basal averostrans such as Ceratosaurus). Ezcurra has used Averostra for the ceratosaur+tetanurine clade in several papers, and in 2007 with Cuny gave it a new node-based phylogenetic definition with that extent- "Ceratosaurus nasicornis, Allosaurus fragilis, and all the descendants of their common ancestor." However, Paul's apomorphy-based definition may not be limited to that clade. Promaxillary fenestrae have since been identified in Dilophosaurus, Zupaysaurus, "Megapnosaurus" kayentakatae, herrerasaurids and Heterodontosaurus. Unfortunately, the phylogenetic position of most of these taxa is controversial, making it difficult to determine which clade an apomorphy-based Averostra designates. In a more traditional topology where coelophysoids are ceratosaurs and/or Dilophosaurus and/or Zupaysaurus are basal coelophysoids, Averostra encompasses at least Neotheropoda sensu Sereno. In alternative phylogenies where Zupaysaurus and/or Dilophosaurus are closer to birds than to Coelophysis, Averostra encompasses at least the former two taxa and perhaps Coelophysoidea (ambiguous since Megapnosaurus and Coelophysis lack promaxillary fenestrae). As derived ornithischians, sauropodomorphs, Eoraptor and Tawa all lack promaxillary fenestrae, it's not certain whether those of herrerasaurids and/or Heterodontosaurus are homologous to theropods'. In a phylogeny like Sereno's where herrerasaurids are sister to avepods (and presumably Tawa), Averostra may encompass the herrerasaurid+avepod clade. No standard topology (where sauropodomorphs and Eoraptor are closer to avepods than ornithischians are) results in Heterodontosaurus' promaxillary fenestra being homologous to theropods' though. With these caveats in mind, Averostra is here provisionally placed at the level of Avepoda.

References- Gauthier, 1986. Saurischian monophyly and the origin of birds. Memoirs of the Californian Academy of Sciences 8, 1-55.
Paul, 1988. Predatory Dinosaurs of the World. Simon and Schuster, New York. 464 pp
Paul, 2002. Dinosaurs of the Air. The John Hopkins University Press, Baltimore and London. 460 pp.
Ezcurra and Cuny, 2007. The coelophysoid Lophostropheus airelensis, gen. nov.: A review of the systematics of "Liliensternus" airelensis from the Triassic-Jurassic outcrops of Normandy (France). Journal of Vertebrate Paleontology. 27(1), 73-86.
Bittencourt Rodrigues, 2010. Revisao filogenetica dos dinossauriformes basais: Implicacoes para a origem dod dinossauros. Unpublished Doctoral Thesis. Universidade de Sao Paulo. 288 pp.

Wednesday, October 27, 2010

Ischigualasto herrerasaurid thoughts

The current consensus is that there are three herrerasaurids in the Ischigualasto Formation of Argentina- Herrerasaurus (including Ischisaurus and Frenguellisaurus), Sanjuansaurus, and the undescribed partial forelimb MACN-PV 18.649a (Ezcurra and Novas, 2007).  But I'm suspicious.

First is the possibility MACN-PV 18.649a belongs to Sanjuansaurus.  The only overlapping elements are the distal ulna, manual ungual and possibly vertebrae.  The unnamed taxon is supposed to have apomorphic Y-shaped side grooves on its manual unguals, which may be visible in Sanjuansaurus (or may be an illusion caused by damage).  It's also supposed to differ from Herrerasaurus in having "subequal ulna-ulnar articular contacts", which I admit to not understanding.

More intriguing is the idea Herrerasaurus has been overlumped.  Novas (1989, 1993) sunk Ischisaurus and Frenguellisaurus into Herrerasaurus, but now that we have additional herrerasaurid taxa from the same formation, this seems less clear.  Most of the differences between Herrerasaurus and Ischisaurus proposed by Reig when he described them were said by Novas to be due to parts of Herrerasaurus paratype PVL 2558 not belonging to the genus.  PVL 2558 includes jaw material with a low number of teeth (3 premaxillary, 8 maxillary, 12 dentary), round alveoli, and a dorsally expanded dentary symphysis.  This differs from the Ischisaurus holotype and paratype, which have four premaxillary teeth, a slender dentary with about 15 teeth, and teeth that are more laterally compressed and recurved.  The latter agrees with specimen PVSJ 407, which Sereno and Novas (1993) described.  Maybe the PVL 2558 cranial material belongs to a crurotarsan or something, but Novas does not give any reasoning for his calling it Archosauria indet. except that it doesn't match with other material he refers to Herrerasaurus.  Even ignoring that though, Reig states the calcaneum of Ischisaurus is larger than Herrerasaurus, and the proximal tibia is "laterally shortened."  These are not addressed by Novas.  Novas (1993) states the Herrerasaurus holotype has shorter posterior dorsal centra than the Ischisaurus holotype, PVSJ 373, 407 and 461, which makes one question his comment earlier on the same page that the Herrerasaurus and Ischisaurus holotypes "exhibit the same autapomorphies and do not exhibit any differences."  Of course those autapomorphies could just be herrerasaurid synapomorphies, as Sanjuansaurus has most them it can be coded for- e.g. narrow, U-shaped antiorbital fossa; spine tables on posterior dorsal and first sacral vertebrae; prominent acromion on scapula; acromial process extends distally with respect to glenoid lip, forms nearly right angle with scapular blade; unexpanded distal scapula; anteroproximal keel on femur; anterolateral subcircular muscle scar on distal femur.  Are Ischisaurus and/or Frenguellisaurus Sanjuansaurus instead?  Also interesting is that Reig states Ischisaurus lacks ventral keels on its cervical centra, while Sereno and Novas (based mostly on PVSJ 407) say Herrerasaurus has them.  Based on this, at least Ischisaurus wouldn't be Sanjuansaurus.  I haven't even looked at Frenguellisaurus yet to see where it fits into this mess.

Even if Ischisaurus and Frenguellisaurus are synonymous with Herrerasaurus, there seems to be the distinct possibility some of the referred Herrerasaurus specimens are actually Sanjuansaurus and/or the unnamed genus.  After all, Sanjuansaurus has almost every supposed Herrerasaurus autapomorphy it can be examined for.  Or would Novas and Sereno sink Sanjuansaurus into Herrerasaurus as well?

Unfortunately, I doubt I'll be able to get much resolved using the literature.  Reig didn't describe the specimens much at all and only illustrated a few elements (pelvis and hindlimb of the Herrerasaurus holotype; dentary of PVL 2558; femur and humerus of the Ischisaurus holotype), while Novas and/or Sereno only illustrate one specimen for each element (except the neck and pelvis, which are composites of several specimens).  Almost all of their descriptions are also composites using several specimens.  So there's no way to check out each specimen and see which characters it has, how it differs from other spcimens, etc.. 

References- Reig, 1963. La presencia de dinosaurios saurisquios en los "Estratos de Ischigualasto" (Mesotriasico Superior) de las provincias de San Juan y La Rioja (República Argentina) [The presence of saurischian dinosaurs in the "Ischigualasto beds" (upper Middle Triassic) of San Juan and La Rioja Provinces (Argentine Republic)]. Ameghiniana. 3, 3-20.

Novas, 1989. The tibia and tarsus in Herrerasauridae (Dinosauria, incertae sedis) and the originn and evolution of the dinosaurian tarsus. Journal of Paleontology. 63, 677-690.

Novas, 1993. New information on the systematics and postcranial skeleton of Herrerasaurus ischigualastensis (Theropoda: Herrerasauridae) from the Ischigualasto Formation (Upper Triassic) of Argentina. Journal of Vertebrate Paleontology. 13, 400-423.

Sereno and Novas, 1993. The skull and neck of the basal theropod Herrerasaurus ischigualastensis. Journal of Vertebrate Paleontology. 13, 451-476.

Ezcurra and Novas, 2007. New dinosaur remains (Saurischia: Herrerasauridae) from the Ischigualasto Formation (Carnian) of NW Argentina. Ameghiniana. 44, 17R.

Thursday, October 21, 2010

Tanystrosuchus- history and relationships

Everyone's talking about Sanjuansaurus, but the interesting Triassic maybe-theropod is surely Tanystrosuchus posthumus.  Generally passed off as an indeterminate theropod or halticosaur, Kuhn might have been right to give it a -suchus suffix after all.

Tanystrosuchus Kuhn, 1963
T. posthumus (Huene, 1908) Kuhn, 1963
= Tanystropheus posthumus Huene, 1908
= Thecodontosaurus posthumus (Huene, 1908) Fraas, 1913
= Halticosaurus posthumus (Huene, 1908) Huene, 1932
= Coelophysis posthumus (Huene, 1908) Olshevsky, 1991

Norian, Late Triassic
Middle Stubensandstein, Germany
(SMNS 4385) distal caudal vertebra (39 mm)

Diagnosis- (after Huene, 1908) no notch between distal caudal prezygapophysis and centrum.
Other diagnoses- Huene (1908) also distinguished posthumus from Tanystropheus conspicuus and T. antiquus based on its supposedly enlarged and elongated postzygapophyses, while the prezygapophyses were said to be rudimentary. Yet he had the vertebra oriented backwards, as it is actually the prezygapophyses which are elongate (65% of central length). Comparably elongate prezygapophyses are known in other taxa such as Effigia, herrerasaurids and many neotheropods. Additionally, the neural spine was said to be more reduced than other Tanystropheus species, and the ventral surface has a median groove instead of being flat and/or keeled. The former is typical of theropod distal caudals while the latter is also found in Effigia and most avepods.
Huene (1932) states a unique character is the lack of elongation, but this varies continuously in most archosaur caudal series.

Tanystrosuchus posthumus holotype distal caudal vertebra SMNS 4385 in right lateral (A) and dorsal (B) views (after Rauhut and Hungerbuhler, 2000). Scale = 10 mm.
Comments- Collected in the 1860's, this was first described and figured by Meyer (1865) as the caudal vertebra of an unknown reptile. Huene (1908) named it Tanystropheus (consistantly misspelled Tanystrophaeus) posthumus, as the elongate cervicals of Tanystropheus were thought to be theropod caudals at the time. SMNS 4385 was noted to be similar to Tanystropheus cervicals in being elongate, lacking transverse processes and having a reduced neural spine. These characters led Huene to refer Tanystropheus to Coeluridae, though they are now recognized as typical features for theropod caudal vertebrae. Today, coelurids and other related basal coelurosaurs are known to be restricted to the Jurassic and Cretaceous and have shorter prezygapophyses than Tanystrosuchus. Both Meyer and Huene had the vertebra backwards, interpreting its elongate prezygapophyses as postzygapophyses.

Fraas (1913) thought much of the Pfaffenhofen quarry material was probably referrable to a small thecodontosaur, which he provisionally used the combination Thecodontosaurus (misspelled Thekodontosaurus) posthumus for. However, posthumus is from the Heslach quarry, not Pfaffenhofen. Fraas did not provide evidence for his reassignment, and Tanystrosuchus differs supposed Thecodontosaurus distal caudals (e.g. YPM 56736) in having a ventral groove, smaller more medially placed postzygapophyses, and larger, longer prezygapophyses.

By 1932, Huene had oriented the vertebra correctly and removed posthumus from Tanystropheus, since new remains of the latter had shown it was a nondinosaurian reptile whose elongated vertebrae were cervicals. He instead called it "Tanystropheus" (gen. indet.) posthumus and assigned it to Coelurosauria, although in one table it is listed as Halticosaurus posthumus. This may have been mistakenly retained from an earlier version of the paper, since he does say posthumus could belong to Halticosaurus or Dolichosuchus. Steel (1970) also suggested posthumus might be referrable to Halticosaurus, while Olshevsky (1991) listed it as possibly being Halticosaurus or Liliensternus (which was placed in Halticosaurus until 1984).

While Halticosaurus and Dolichosuchus are known from the same formation (but different quarries), they do not preserve distal caudal vertebrae so cannot be compared. Liliensternus loses its transverse processes on caudal 22 and its neural spines at about caudal 30. This fits with Tanystrosuchus' holotype being most similar in proportions to caudal 32 of those illustrated for Liliensternus. It differs from Liliensternus in having longer prezygapophyses (65% of central length compared to 17-22%), less dorsally projected zygapophyses, and lacking a notch between the prezygapophysis and centrum. These seem to be true in all illustrated caudals similar in position to Tanystrosuchus' (20, 24, 32, 38), so probably indicate it is not synonymous.

Kuhn (1963) created the new genus Tanystrosuchus for posthumus, as he also decided it was not referrable to Tanystropheus. Wild (1973) also rejected the synonymy of posthumus with Tanystropheus conspicuus. Tanystrosuchus differs from Tanystropheus in having longer prezygapophyses and lacks Tanystropheus' tall bladelike neural spine. In 1965, Kuhn stated Tanystrosuchus might be protorosaurid instead of dinosaurian. Yet Protorosaurus distal caudals differ in having short prezygapophyses, longer postzygapophyses, knob-like transverse processes and a tall bifurcated neural spine.

Norman (1990) noted the long prezygapophyses were suggestive of theropod relationship, but considered it a nomen dubium. Olshevsky (1991) placed Tanystrosuchus in Halticosauridae and listed the combination Coelophysis posthumus as a prior synonym, though I have yet to locate this in an earlier published work. Glut (1997) merely listed the genus as a nondinosaurian reptile. Most recently, Rauhut and Hungerbuhler (2000) briefly redescribed and illustrated the material, listing it as Tanystrophaeus posthumus. Their conclusions match Norman's- that it is an indeterminate theropod based on the prezygapophyseal length.

Tanystrosuchus is similar to coelophysoids in general form- elongate amphicoelous centrum (3.25 times longer than tall) with median ventral groove, neural spine reduced to a slight ridge over the postzygapophyses, transverse process reduced to a longitudinal ridge, elongate prezygopophysis and short postzygapophysis. However, the prezygapophysis is actually longer than in coelophysids, 65% of central length compared to 35% in Megapnosaurus, 25% in Coelophysis, 22% in Liliensternus and 37% in Dilophosaurus. In this respect Tanystrosuchus is more similar to herrerasaurids and neotheropods (e.g. Elaphrosaurus). It differs from herrerasaurids in having the ventral groove and from known neotheropods in being Triassic in age, though if coelophysoids are monophyletic we would expect Norian neotheropods. Another perhaps more plausible identification is as a shuvosaurine, which are common in the Late Triassic. Effigia has distal caudals which exhibit the same characters noted above for coelophysoids (including the ventral groove), except its prezygapophyses are longer (at least 58% of central length). The preserved caudals have neural spines, albeit low ones, but these are all proximal to the thirtieth caudal and it is probable that more distal ones lacked neural spines as in theropods and Tanystrosuchus. It differs from all examined theropods and Effigia in lacking a notch between the prezygapophysis and centrum.

While the anatomy favors a shuvosaurine or neotheropod identification, stratigraphy favors the former only to the extent that Triassic shuvosaurines are certainly known while Triassic neotheropods are unknown but possible depending on theropod topology. Also a factor is that variation along the tail is poorly described for most taxa discussed here, so while the published evidence suggests coelophysoid prezygapophyses never exceed half of centrum length and herrerasaurids lack ventral grooves, this is not as well established as it could be. For now, I recommend Tanystrosuchus posthumus be referred to Archosauria incertae sedis.

References- Meyer, 1865. Reptilien aus dem Stubensandstein des oberen Keupers (Dritte Folge). Palaeontographica. 14, 99-124.

Huene, 1908. Die Dinosaurier der europäischen Triasformation mit Berücksichtiging der aussereuropäischen Vorkommnisse [The dinosaurs of the European Triassic Formation, with consideration of non-European occurrences]. Geologische und Paläontologische Abhandlungen Supplement-Band. 1, 419 pp.

Fraas, 1913. Die neuesten Dinosaurierfunde in der schwäbischen Trias [The newest dinosaur finds in the Swabian Trias]. Naturwissenschaften. 1(45), 1097-1100.

Huene, 1932. Die fossile Reptil-Ordnung Saurischia, ihre entwicklung und geschichte. Monographien zur Geologia und Palaeontologie. 1, 1-362.

Kuhn, 1963. Sauria (Supplementum I). In Fossilium Catalogus I. Animalia. 104. 87 pp.

Kuhn, 1965. Saurischia (Supplementum 1). In Fossilium Catalogus 1. Animalia. 109, 94 pp.

Steel, 1970. Part 14. Saurischia. Handbuch der Paläoherpetologie. Gustav Fischer Verlag, Stuttgart. 1-87.

Wild, 1973. Die Triasfauna der Tessiner Kalkalpen. XXIII. Tanystropheus longobardicus (Bassani) (Neue Ergebnisse). Schweizerische Palaontologische Abhandlungen. 95, 1-162.

Norman, 1990. Problematic Theropoda: "Coelurosaurs". in Weishampel, Dodson and Osmolska (eds). The Dinosauria. University of California Press: Berkeley. 280-305.

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

Glut, 1997. Dinosaurs - The Encyclopedia. McFarland Press, Jefferson, NC. 1076 pp.

Rauhut and Hungerbuhler, 2000. A review of European Triassic theropods. Gaia. 15, 75-88.