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.

Thursday, October 14, 2010

Goniopoda, Harpagosauria and Carnosauriformes - Theropoda alternatives

Theropoda is a term entrenched in the literature for carnivorous dinosaurs, but it's had competition over the years.  Today we'll reflect on these alternative names for the group.

Cope (1866) named Goniopoda for Dryptosaurus (his Laelaps) and Streptospondylus (his Megalosaurus) based on his misinterpretation of their astragalus as the fibula, as a fibula which wraps distally around the tibia would be unique. The taxon was almost exclusively used by Cope through the 1880's, who eventually gave it a scope and diagnosis similar to Marsh's Theropoda (e.g. Cope, 1883). After Cope's death, Theropoda became the term exclusively used for carnivorous dinosaurs.

Harpagosauria was seen as a paraphyletic order of dinosaurs by Haeckel (1866), containing Megalosaurus, Plateosaurus and Pelorosaurus (but not Iguanodon). Haeckel refers to these as the carnivorous dinosaurs, which led Cope to synonymize the taxon with his Goniopoda (starting in 1870, and consistantly misspelled Harpagmosauria). However, Haeckel's original usage suggests it is instead the equivalent to Saurischia. Baur (1887) uses Harpagosauria as a dinosaurian group containing only Goniopoda, with Sauropoda separate. Haeckel (1895) later used Harpagosauria as a junior synonym for his new dinosaurian taxon Dysdracones including both Arctopoda (containing basal sauropodomorphs) and Theropoda, with sauropods now placed in his Eudracones that contained all herbivorous dinosaurs. Harpagosauria was said by Haeckel to contain the carnivorous dinosaurs with sharp teeth and claws. It has not been used since.

Proposed as part of a cladistic reclassification of ornithischians, Carnosauriformes was named by Cooper (1985) as a cohort of dinosaurs "retaining the primitive condition of recurved thecodontian dentition with finely serrated cutting edges." No justification for using this name over Theropoda was given, and it is today rightfully considered a junior synonym.

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.

Haeckel, 1866. Generelle Morphologie der Organismen. Allgemeine Grundzuge der organischen Formen Wissenschaft, mechanisch begrundet durch die von Charles Darwin reformiete Deszendenz-Theorie. II. Allgemeine Entwicklungsgeschichte der Organismen. Kritische Grundzuge der mechanischen Wissenschaft von dan entstehenden Formen der Organismen, begrundet durch die Deszendenz-Theorie. Georg Reimer, Berlin. 462 pp.

Cope, 1870. Synopsis of the extinct Batrachia and Reptilia of North America. Transactions of the American Philosophical Society. 14, 1-252.

Cope, 1883. On the characters of the skull in the Hadrosauridae. Proceedings of the Philadelphia Academy of Natural Sciences. 35, 97-107.

Baur, 1887. On the phylogenetic arrangement of the Sauropsida. Journal of Morphology. 1, 93-104.

Haeckel, 1895. Systematische Phylogenie: Entwurf eines Natürlichen Systems der Organismen auf Grund ihrer Stammesgeschichte. Dritter Theil: Systematische Phylogenie der Wirbelthiere (Vertebrata). Georg Reimer, Berlin. 660 pp.

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.

"The Princeton Field Guide to Dinosaurs" - The Ornithischians

Finishing up the review series is this post on ornithischians.  As with sauropodomorphs, these aren't my speciality, so I don't have educated opinions on most of the issues nor do I always know exactly what the latest consensus is.  Honestly, the same kinds of problems are present in this section as the previous one.  I think I've figured out Paul's splitter/lumper methodology though.  If a taxon is similar to another, but from a different horizon, it's a different species!  Doesn't matter if anyone's actually tried to name a distinct taxon from there yet, or if there are actually any differences reported in the literature.  If a taxon is from the same horizon as another similar one, they're synonymous!  Ignore priority and use the name of the most complete specimen for the taxon.  If a species forms a clade with another, they're congeneric!  With these three easy steps, you too can lump and split the GSP way. ;)

As with the other sections, there are many excellent reconstructions.  My favorites are Scutellosaurus, Gigantspinosaurus, Saichania, Pinacosaurus, Ankylosaurus, Edmontonia, Archaeoceratops, Prenoceratops, Montanaceratops, Talenkauen, Gasparinisaura, Muttaburrasaurus, Probactrosaurus, Tethyshadros, and the many derived hadrosaurs.  It's nice to see the ankylosaurs and hadrosaurs reconstructed, since usually people only bother with their skulls.

Like theropods, thyreophorans unjustly suffer from the statement "absence from Antarctica probably reflects lack of sufficient sampling." Despite the fact Antarctopelta is known AND included in the book.  Chungkingosaurus and Chialingosaurus are said to probably be juvenile Tuojiangosaurus, but the former is a diagnostic huayangosaurid (Maidment and Wei, 2006) and the latter has priority over Tuojiangosaurus.  Upper Tendaguru Kentrosaurus remains "probably belong to a different taxon" while Stegosaurus longispinus "probably is a more basal stegosaurid."  These may be true, I don't know.  Amusingly, Wuerhosaurus "is not a species of Stegosaurus as has been suggested."  I'm not sure why Paul's lumpometer fails here.  For "Hesperosaurus (or Stegosaurus) mjosi", "Lack of limbs hinders assessing whether this is a Stegosaurus as some reseachers have concluded."  Because Stegosaurus is apomorphy-defined using limb characters?

Dracopelta, Shamosaurus, Gobisaurus, Stegopelta, Niobrarasaurus and Antarctopelta are listed as "polacanthians."  Good ol' nonexistent Polacanthia...  I'm unaware of these taxa even being referred to Polacanthidae.  Pinacosaurus mephistocephalus is listed as a synonym of P. grangeri and Struthiosaurus languedocensis "may be the adult" of S. austriacus.  Again, are these plausible?  I don't know.  But claiming Pawpawsaurus "probably includes Texasetes pleurohalio" is certainly incorrect, as Texasetes has priority.  "Euoplocephalus tutus" is placed in quote marks, said to have an inadequate holotype and said to possibly consists of multiple taxa.  Horseshoe Canyon specimens are assigned to ""Euoplocephalus" unnamed species?" though, presumably because they're from a different formation.

Butler will be surprised to hear Heterodontosaurus "probably includes the smaller, tuskless Abrictosaurus consors as well as Lycorhinus angustidens."

Homalocephalids are said to probably be immature pachycephalosaurids or females, which leads to "Goyocephale (or Stegoceras) lattimorei" and "Prenocephale (or Stegoceras) prenes" with Homalocephale "probably an immature P. prenes."  There's also "Tylocephale (or Stegoceras) gilmorei."  Even if he's right about homalocephalids, none of the Asian taxa are especially close to Stegoceras.  Of course Paul's Stegoceras is a huge para/polyphyletic mass including every non-Pachycephalosaurus North American taxon at least, since Stegoceras? brevis "may include Colepiocephale lambei", and Stegoceras validum "may include Hansuessia sternbergi."  Dracorex and Stygimoloch are probably juvenile Pachycephalosaurus "in which case the spikes are a sexual characteristic, or there may be two species, the other being P. spinifer." But what about the spikes being resorbed?

The only new non-theropod taxonomic name proposed in the book is Paxceratopsia for psittacosaurs and neoceratopsians, but not chaoyangosaurs.  Psittacosaurus meileyingensis "probably includes P. ordosensis", Udanoceratops "may include Bainoceratops efremovi" and Gobiceratops "may be a juvenile" Bagaceratops.  Again, I'm not sure if these are plausible.  I was disappointed to see all non-ceratopsid neoceratopsians called protoceratopsids.  Cerasinops is listed twice in the book, with identical entries at least.  For ceratopsids, Paul has the odd division between centrosaurines, chasmosaurines AND ceratopsines.  Err.... Paul includes only Triceratops and Avaceratops in Ceratopsinae and says "The existence of this group is not certain." Well, since it's never been recovered in an analysis and there's no reason Ceratops itself is close to either genus, I suppose that's true.  Paul's ceratopsids are lumped like there's no tomorrow.  There's "Albertoceratops (=Diabloceratops) eatoni".  All other centrosaurines are Centrosaurus, so we get Centrosaurus (=Styracosaurus) albertensis, C. (=Styracosaurus) ovatus, C. (=Einosaurus[sic]) procurvicornis, C. (=Achelousaurus) horneri, C. (=Pachyrhinosaurus) lakustai, and C. (=Pachyrhinosaurus) canadensis.  But Centrosaurus nasicornis and C. apertus are separate, no doubt because they're from different levels of the Dinosaur Park.  Not only is such lumping pointless, IF it were true, Monoclonius would be the proper genus since crassus is definitely somewhere in that clade.  For chasmosaurines, we get Chasmosaurus (Pentaceratops = Agujaceratops) mariscalensis and Chasmosaurus (Pentaceratops) sternbergi.  Which makes both Chasmosaurus and the supposed subgenus Pentaceratops para/polyphyletic.  And of course Triceratops is lumped, with Triceratops (=Eotriceratops) xerinsularis, and Nedoceratops (incorrectly listed as Diceratops) a synonym of T. horridus

Moving on to ornithopods, Hexinlusaurus "is probably immature example of" Agilisaurus louderbacki.  Even though the former is closer to ornithopods in Butler's tree.  Then we have "Agilisaurus? unnamed species" which was "named Yandusaurus hongheensis based on inadequate remains."  Not only is Yandusaurus closer to ornithopods than Agilisaurus, but Yandusaurus has priority over Agilisaurus AND how can you have an unnamed species that used to be a named species?!  More predictably bad taxonomy- Othnielosaurus consors was "once Othnielia rex."  More like Othnielia isn't necessarily OthnielosaurusAnabisetia, Gasparinisaura, Talenkauen, Thescelosaurus and Parksosaurus are all listed as hypsilophodonts, but are iguanodonts.  Iguanodonts also get the old "absence from Antarctica probably reflects lack of sufficient sampling" treatment, but there's a hadrosaur from there (Case et al., 2000).  The Tenontosaurus dossi cranial reconstruction doesn't have premaxillary teeth.  For rhabdodont lumping, Rhabdodon (=Zalmoxes) robustus "probably includes Z. shqiperorum."  But then for horizon-based splitting, "Dryosaurus unnamed species" (for Utah Middle Morrison remains) is "usually placed in D. altus but probably is a different species than the latter dryosaur, and differing genera cannot be ruled out."  The placement of taxa in Paul's iguanodont grades seems problematic, with e.g. Planicoxa being a dryosaur.  I was amused that Paul's own taxon Dollodon bampingi is misspelled "bambingi" every time.

Finally, there's the lumptastic hadosaurs.  It honestly looks like Paul just used a twenty-year old classification and applied his three lumping/splitting steps.  Bactrosaurus "probably includes Gilmoreosaurus mongoliensis." We get Saurolophus (=Lophorthothon[sic]) atopus, Saurolophus (=Prosaurolophus) blackfeetensis, and Saurolophus (=Prosaurolophus) maximusLophorhothon isn't even a hadrosaurid, while blackfeetensis is a synonym of maximus, but silly me it's from a different formation.  Maisaura (or Brachylophosaurus) peeblesorum "may be a subgenus of Brachylophosaurus", which is just meaningless.  There's Kritosaurus (or Gryposaurus) latidens, notabilis, incurvimanus, and monumentensis and Kritosaurus (or Anasazisaurus) horneri.  Last I heard, horneri was a synonym of navajovius, incurvimanus was a synonym of notabilis, and you'd need to put Secernosaurus in Kritosaurus if you put Gryposaurus there.  Most sadly, we have Aralosaurus (or Kritosaurus) tubiferus, despite the fact Aralosaurus is a lambeosaurine.  Pararhabdodon "probably includes Koutalisaurus", which agrees with Prieto-Marquez.  Parasaurolophus walkeri and "P. tubicen are not distinctive from one another, and short crested New Mexican P. cyrtocristatus may be a female or subadult of this species."  I'm not sure about the evidence for that.  Olorotitan "may be the same genus or species as Amurosaurus riabinini", which is untrue as they're not closely related within Lambeosaurinae.  We get both Nipponosaurus (or Hypacrosaurus) sachaliensis and Barsboldia (or Hypacrosaurus) sicinskii, though the latter is a saurolophine.  In fact, all the helmet-crested lambeosaurines get placed in one genus.  There's Hypacrosaurus (=Velafrons) coahuilensis, Hypacrosaurus (=Corythosaurus) casuarius and intermedius, Hypacrosaurus (=Lambeosaurus) clavintialis, lambei and mangicristatus, and Hypacrosaurus? laticaudus.  Again, I didn't think clavintialis was valid, while you'd need to put Amurosaurus and Sahaliyania in Hypacrosaurus too if you're lumping like that.

And that's it.  Be sure to check out Jaime Headden's review and future commentary too.

Friday, October 8, 2010

"The Princeton Field Guide to Dinosaurs" - The Sauropodomorphs

Part 3 of the review series, I should preface this by saying that sauropodomorphs aren't my speciality.  I don't follow the literature closely, so I don't know if some of Paul's nonstandard ideas have been proposed before, or how likely they are to be correct.

As with the theropods, the reconstructions are plentiful.  My favorites include Massospondylus, Lufengosaurus, Yunnanosarus, Jingshanosaurus, Riojasaurus, Gongxianosaurus, Datousaurus, Cetiosaurus and Atlasaurus.

Among non-sauropods, Paul doesn't follow the consensus in a few areas.  Ammosaurus is listed separately from Anchisaurus, Ruehleia is said to be an adult Plateosaurus longiceps, Efraasia is back to being a juvenile Plateosaurus gracilis and P. longiceps is kept separate from P. engelhardti.  He only does a little lumping, with "Massospondylus (or Plateosaurus = Lufengosaurus) huenei" and "Massospondylus (or Plateosaurus) carinatus".  Plateosaurus is usually not in an exclusive clade with Lufengosaurus and Massospondylus, so this seems like an improper synonymy.  Even synonymizing Lufengosaurus with Massospondylus seems wrong if Adeopapposaurus and Coloradisaurus are retained in their own genera.  In the first of a few examples to be noted here, Paul says Plateosauravus cullingworthi "was Euskelosaurus browni, which is based on inadequate remains."  Argh.  Euskelosaurus can't become Plateosauravus since the former has priority.  According to Yates (2004), Euskelosaurus really is indeterminate and could belong to Plateosauravus or an undescribed prosauropod from the Clocolan District.

Among sauropods, Klamelisaurus is treated as adult Bellusaurus, which I know was suggested, but has anyone actually examined this issue?  The mamenchisaurids suffer quite the deconstruction.  I agree with Paul that the alpha taxonomy on these things needs to be examined, but since Paul's rationale is never explained and even his intent is sometimes ambiguous, I can't say he sheds much light on the issue.  tianfuensis is said not to be Omeisaurus (it is "too different"), while maoianus is placed in the genus with a question mark.  hochuanensis and youngi are both said to be in the same genus and perhaps just different sexes of the same species.  They're also excluded from Mamenchisaurus based in part on M. constructus having a shorter neck, though I was under the impression M. constructus' cervicals were simply incomplete so restored as being short.  Paul also lists (quotation marks his) "Mamenchisaurus" anyuensis, "Mamenchisaurus sinocanadorum" and "Mamenchisaurus jingyanensis."  The latter is said to probably belong to one of the other Shangshaximiao species.  While the quotation marks would seem to indicate Paul doesn't think anyuensis belongs in Mamenchisaurus, I'm not sure what they imply for sinocanadorum and jingyanensis (both were properly described, so are not nomina nuda).

Among diplodocids, Paul lists "Amphicoelias or Diplodocus altus" and says "Status not certain, may be a distinct genus or Diplodocus."  Ack again.  Diplodocus altus can never exist, as Amphicoelias has priority over it.  There's an unnamed species of Diplodocus listed from Utah represented by "two skulls and majority of a few skeletons."  It's illustrated with a complete skeleton and is listed separately from D. longus, D. carnegii, D. hayi and D. halli (wasn't this emmended to hallorum?).  Anyone know if the literature supports this?  Paul seems to place Apatosaurus parvus, A. excelsus and A. louisae in the subgenus Brontosaurus, which contradicts Upchurch et al.'s (2004) study that found parvus and excelsus to be closer to ajax than to louisae.  His statement "Brontosaurus is the shorter, narrower necked version of Apatosaurus from the lower and middle Morrison" wouldn't be agreed on by sauropod experts as far as I know.  It's these kinds of statements which make me cringe imagining kids reading the book, since they're just stated as true despite being found nowhere in the literature.

Paul excludes ruyangensis from Huanghetitan and giganteus from AntarctosaurusPitekunsaurus is said to be "probably a juvenile of one of the other Anacleto titanosaurs."  I have no idea is these things are plausible.  While I can never keep track of the metric crapload of titanosaurs being described these days, things like placing Isisaurus outside Lithostrotia but including Huabeisaurus don't seem to mesh with even the pitiful amount of consensus that has been reached regarding their phylogeny.  I also don't think the evidence justifies synonymizing Opisthocoelicaudia skarzynskii with Nemegtosaurus mongoliensis or placing Quaesitosaurus in the same genus.  It's not like formations with more than one sauropod are uncommon, and I'm doubtful Nemegtosaurus' sister genera have skulls preserved.  Finally, Pleurocoelus is said to be "originally Astrodon johnstoni, which was based on inadequate remains."  But just like with Euskelosaurus, Astrodon has priority over Pleurocoelus so can never become Pleurocoelus.

Next up, ornithischians *yawn* ;)

Thursday, October 7, 2010

"The Princeton Field Guide to Dinosaurs - The Theropods

Having reviewed Paul's new book in the last post, this one will examine the good, bad and just plain interesting things it has to say about theropods.  It's organized in the order Paul discusses the taxa.

The seemingly rigorous Staurikosaurus skeletal includes anterior cervicals, chevrons, the whole pectoral girdle, a humerus and pes.

The coelophysoids have meager descriptions as with most taxa, but most every skulless one (Procompsognathus, Podokesaurus, Gojirasaurus, Liliensternus, Segisaurus, but not Lophostropheus) contains the phrase "not known whether head crests were present."  This is repetitive (it would be simpler to say only Megapnosaurus and Coelophysis are known to LACK crests) and you would think there's more useful information the space could be spent on, like Gojirasaurus being a chimaera, Procompsognathus being perhaps nondinosaurian and with a controversial skull, Segisaurus being thought to have solid bones and unfused clavicles until recently, etc..

Among abelisaurs, the Rahiolisaurus skeleton is labeled Indosuchus and seems to just be reposed from Chatterjee and Rudra's schematic drawing (which is now known to be wrong in various ways thanks to the description).  A complete skull is illustrated and listed for Rajasaurus, but while there is a cast that's often photographed, only a braincase is present according to the description.  For those curious why Aucasaurus is sunk into Abelisaurus- "the only reason this does not appear to be a juvenile A. comahuensis is that fusion of skeletal elements suggests it is an adult."  It should be noted Paul has an odd phylogeny where ceratosaurids and elaphrosaurs are closer to tetanurines than abelisauroids are. The seemingly rigorous Elaphrosaurus skeletal incorrectly has a complete vertebral column, all chevrons (only one is preserved) and complete pes, but doesn't include the scapulocoracoid or metacarpals.

Poekilopleuron bucklandii being the same genus and/or species as Megalosaurus bucklandii might have been a viable idea back in 1988, but not now that both have been redescribed.  Another odd aspect to Paul's phylogeny is that Piatnitzkysaurus, Condorraptor, Magnosaurus, Eustreptospondylus (as Streptospondylus) and Afrovenator are avetheropods.  The rationale for sinking Eustreptospondylus- "Eustreptospondylus oxoniensis is tentatively placed in Streptospondylus altdorfensis."  Eustreptospondylus' skeletal is odd in lacking most of the skull besides the premaxilla, maxilla and quadrate, but a lot of what is shown is not preserved (ribs, most caudal vertebrae, chevrons, etc.).

Sinraptor hepingensis is synonymized with Yangchuanosaurus shangyouensis, but S. dongi (with a humerus and coracoid in its rigorous skeletal) is kept separate.  Monolophosaurus and Guanlong are both sinraptorids, which has never been supported to my knowledge.  Paul retains the old short snout vs. long snout Allosaurus dichotomy which Chure has showed is untrue.  For Neovenator, he states "That researchers have disagreed whether this is a basal tyrannosauroid or an allosauroid suggests these groups may be more closely related than thought."  But whoever proposed Neovenator is a tyrannosauroid?

For Coelurosauria, Paul states "The validity of the group is not certain."  But who has ever had a theropod phylogeny without it? While I do applaud Paul's indicating when taxa are based on juvenile specimens, he's incorrect in calling the heavily fused Bagaraatan type a juvenile and the young Raptorex type an adult.  On the other hand, I was happy to see him call both Alioramus species juveniles and probably synonymous.  One new combination missing in my taxonomy post is "Appalachiosaurus (or Albertosaurus) montgomeriensis."  Using Carr's data, that seems fine as long as Bistahieversor is Albertosaurus too.

Paul lumps all American ornithomimids into Struthiomimus, but says Struthiomimus? sedens "includes Ornithomimus velox, which is based on entirely inadequate remains."  GAK!!!  Impossible.  Ornithomimus and the species velox have priority over Struthiomimus and sedens.  If Ornithomimus' syntypes are entirely inadequate (and they're not), it couldn't be assigned to the same species as sedens

The rigorous Ornitholestes skeletal lacks any forearm or manus material (even though the famous manus has been reassigned to Tanycolagreus, the holotype has manus material as well).  Scansoriopteryx is used instead of Epidendrosaurus, which is nice.  Yet the taxon is not placed with Epidexipteryx, as the latter is assigned to Oviraptorosauria instead.  Wherever the taxa belong, their morphology is so similar that they may even be synonymous.  If Paul would have used all the manual phalanges in Epidexipteryx, he would have found it impossible to restore with normal hands.

Shanag is sunk into Sinornithosaurus because "Too little is known to distinguish this from Sinornithosaurus."  Tsaagan and Graciliraptor don't even get that much explanation.  Deinonychus' skeletal is oddly incomplete (no scapula, humerus, ilium, pubis, femur, tibia or fibula), which I'm assuming is due to Paul's statement Lower Cloverly remains "are probably one or more different taxa."

The oviraptorosaurs are all given bifurcated tail fans, but Gatesy (2001) showed this was an illusion in Caudipteryx.  Both Epidexipteryx and omnivoropterygids are placed in Oviraptorosauria, which has never been supported by an analysis, but I do like that Paul uses Omnivoropterygidae instead of Sapeornithidae.  The caenagnathid taxonomy is highly confused.  Using Paul's names, it consists of- Caenagnathus collinsi (only the type mandible), Caenagnathus? sp. (the two undescribed Triebold skeletons), Chirostenotes pergracilis (said to possibly include elegans), Chirostenotes? sp. (the specimen described in Sues, 1997), and Elmisaurus (or Chirostenotes) rarus.  Where to begin?  The Triebold skeletons combine Caenagnathus jaws with Chirostenotes postcrania, so there's no reason to keep the genera separate, let alone refer the Triebold material to one genus or the other.  elegans is more similar to Elmisaurus despite the undefended assertions of some recent papers (Sues, 1997; Maryanska et al., 2002; Osmolska et al., 2004).  The Horseshoe Canyon specimen described by Sues has never been suggested to belong to a distinct taxon in the literature, and was seemingly just separated based on stratigraphy.  Shanyangosaurus is listed as a caenagnathid, which I find amusing since I suggested it was an oviraptorosaur back in 2000, that was also followed by Holtz et al. (2004).  Ironically, I no longer think my analysis was sufficient to place it anywhere specific within Maniraptora.

Oviraptorids themselves were lumped a lot. For Citipati osmolskae, Paul says "It is probable that crestless Khaan mckennai is the juvenile form of this species."  And for "Conchoraptor (or Citipati) gracilis", he says "It is probable that all specimens from this formation are juveniles and adults of one species whose taxonomy is complicated because the genus portion of the original name Ingenia yanshini turned out to be preoccupied by an invertebrate."  But as I noted before, just because Ingenia is preoccupied doesn't mean yanshini wouldn't still be the species name.  Nor can Conchoraptor gracilis ever be Citipati gracilis, since Conchoraptor has priority over Citipati.  His illustration for this conglomerate of taxa is basically "Ingenia" but with that privately owned skull with the very tall pointed crest.  I do like that Paul illustrates the internal nostrils on the side of the ventrally projected palate in oviraptorids.

The reconstruction of Beipiaosaurus uses the new anterior skeleton and features a silly-looking vaguely stegosaur-like skull with a pointy snout.  Contra to Paul who thinks Nothronychus graffami (mistyped grafmani) might be synonymous with N. mckinleyi, I'm doubtful they're even congeneric.

Next up, sauropodomorphs...

Wednesday, October 6, 2010

"The Princeton Field Guide to Dinosaurs" - The Review

One of the perks to working at a bookstore is being able to borrow books, and today I checked out Gregory S. Paul's newest work.  My comments before have been based only on the snippets available on Google Books, which isn't exactly fair.  I'm only going to concentrate on the theropod section for examples, since that's what I'm most familiar with.

When people think 'Gregory S. Paul', they think excellent skeletals and restorations, and this book's overflowing with them.  My theropod favorites include Limusaurus, Acrocanthosaurus, Sinornithomimus, NGMC 2124, Sinocalliopteryx, Buitreraptor, Jinfengopteryx, Mei, the Two Medicine Troodon, Sapeornis and Protarchaeopteryx.  One thing I like is how many are rigorous in showing only the known material.  The unfortunate counterpoint is that that leaves one thinking the reconstructions which are complete indicate complete skeletons are known, but this is often not the case.  I also liked the PDW way of illustrating skulls better, with thinner lines and texturing.  The life restorations are spectacular as always.  I love the Dromiceiomimus scraping eggs and the Sinosauropteryx leaping for a Confuciusornis as two modern updates to classic themes.

The other thing people think of when they hear 'Gregory S. Paul' is taxonomic lumping. ;)  As I described in this post, he lumps a LOT of taxa together.  I think this will be confusing to most readers, who won't realize a lot of these new combinations aren't found in the literature.  While sometimes Paul notes what he changes in the taxonomy, he almost never states when something is his unique idea, or followed by other researchers.  Interestingly on page 42 he states "The phylogeny and taxonomy offered here are not a formal proposal."  This would seem to qualify for ICZN Article 8.2- A work that contains a statement to the effect that it is not issued for public and permanent scientific record, or for purposes of zoological nomenclature, is not published within the meaning of the Code.  So perhaps Paul's new combinations are all nomina nuda.

Interestingly, Paul may lump genera and many species, but he also features a wide range of unnamed species.  These include Padian's (1986) Coelophysis, the supposed Morrison Elaphrosaurus, Portuguese Ceratosaurus, problematic long-snouted Allosaurus, Dinosaur Park and Two Medicine Daspletosaurus, Dinosaur Park Struthiomimus, NGMC 2124, and Triebold and Horseshoe Canyon caenagnathids.  While some of these have been proposed in the literature, others haven't and seem to be largely stratigraphy-based.  I think the space would have been better spent including additional named taxa, such as Halticosaurus, Genyodectes, Betasuchus, Velocisaurus, Chuandongocoelurus, Erectopus, Metriacanthosaurus, Becklespinax, Archaeornithoides, Variraptor, Borogovia, etc.. 

The first 63 pages consist of standard introductory material- anatomy, behavior, trackways, history, extinction, etc..  It's largely what one finds in many dinosaur books, but is more accurate than any others I can recall.  One unique section is "Dinosaur Safari", which playfully imagines how human time travelers might deal with the Mesozoic.  I do think the book could have benefited from an additional editor besides Kirkland, as there are occasional typos (the Landian stage of the Middle Triassic, Pycnoneosaurus, Ricardoesteria, protoarchaeopterygids, etc.).  Also the accuracy of the temporal distribution of different groups on the timescale of pages 64-65 is subpar, with most maniraptoriform clades appearing too late for instance.

The main portion of the book is of course the taxonomic section.  I stand by my previous complaint that this is not effective as a field guide, since nearly all the taxa lack any useful description or indication of diagnostic features.  It's more like Sattler's 1983 "The Illustrated Dinosaur Dictionary" or Lambert's 1990 "The Dinosaur Data Book", with less information on each taxon than the former, but much more than the latter.  It's also more technical than either in including species, stages, formations and more anatomical terms.  Yet it's also less complete than either, and while obviously you can't reconstruct Ornithodesmus or Bradycneme, I don't think I'm alone among dinosaur enthusiasts in wanting my books to include every taxon.

The descriptions that do exist are often so vague as to be pointless.  For instance, coelurosaurs are described as follows- "Highly variable. Tail long to very short. Arm from longer than leg to severely reduced. Leg extremely gracile to robust, toes four to three."  Well... I guess some amphiumas and sloths are excluded at least. ;)  That doesn't tell you anything about what distinguishes the group.  The individual species descriptions suffer the same problem, when they mention any features at all.  And a disturbingly large number of taxa are merely said to be standard for their group, including rather distinctive ones such as Herrerasaurus, Segisaurus, Noasaurus, Torvosaurus, Piatnitzkysaurus, Eustreptospondylus, Gasosaurus, Siamotyannus, sinraptorids, Carcharodontosaurus, Giganotosaurus, Mapusaurus, Mononykus, Mahakala, Sinornithoides, Nanshiungosaurus and Erliansaurus.  Others are said to have insufficient information, but it's inconsistantly applied.  While Duriavenator and Ilokelesia get a description, Elaphrosaurus, Elmisaurus and Neimongosaurus don't.

The theropod groups (Theropoda, Tetanurae, Coelurosauria, Maniraptora, etc.) are never implied to include pygostylians in the introductory sections, so reading that e.g. maniraptorans only lasted to "the end of the dinosaur era" is rather odd.  All major theropod taxa have the following in their notes- "absence from Antarctica probably reflects lack of sufficient sampling."  Not only is it repetitive, it's unecessary since we have both Molnar et al.'s (1996) basal tetanurine tibia and Case et al.'s (2007) supposed dromaeosaur from the continent.  The habits section gets particularily speculative.  For instance, herrerasaurs are said to be pursuit predators.  Really?  Of the included taxa, Alwalkeria and Chindesaurus are far too poorly known, Eoraptor seems omnivorous and Herrerasaurus is massively built with shorter tibiae than femora.  I suppose Staurikosaurus may have been, but the topic has never been studied to my knowledge.  One excellent practice is taxa known only from young specimens aren't given a size and are instead marked "Adult size not certain."

"The Princeton Field Guide to Dinosaurs" is thus extremely accurate in general and full of amazing artwork, but isn't very useful for learning about individual dinosaur species or groups.  It also contains a lot of information which is not based on the literature and often contradicts the consensus, which most readers won't know.  I'd recommend it for young readers who aren't ready for Glut's encyclopedias or The Dinosauria yet.

Next up, theropod criticism and commentary.

Paul, 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press. 320 pp.

Tuesday, October 5, 2010

But this C. longicollis syntype isn't Cloelophysis

Again, something I noticed while cataloging past Coelophysis diagnoses.  Back in 1887, Cope noted that what would be named Coelophysis (Coelurus longicollis and bauri at the time) differs from Anchisaurus (his Megadactylus) and Megalosaurus in lacking an ectocondylar tuber on the femur.  This is also mentioned as a diagnostic character in his 1889 note naming Coelophysis.  This caught my eye since I had just dealt with ectocondylar tubers for Kayentavenator.  So I checked Huene's (1906, 1915) papers describing and illustrating the original Coelophysis material, and indeed the complete syntype femur of C. longicollis (AMNH 2704) lacks an ectocondylar tuber.  This is unlike theropods (or shuvosaurids, which C. bauri syntype femur AMNH 2725 was referred to by Nesbitt et al., 2007), but is similar to silesaurids like Silesaurus and Eucoelophysis.  Also like silesaurids but unlike theropods, the femoral head is parallelogram-shaped instead of distinctly offset.  Rather unsurprisingly, it seems to have autapomorphies of the contemporaneous Eucoelophysis (after Ezcurra, 2006)- no trochanteric shelf, reduced fourth trochanter.

Femora in lateral and anterior view of (left to right) Silesaurus (after Dzik, 2003), Eucoelophysis (after Ezcurra, 2006), Coelophysis longicollis syntype AMNH 2704 (after Huene, 1915), and Coelophysis bauri with proximal lateral view of kayentakatae (after Spielmann et al., 2007 and Rowe, 1989 respectively).

This underscores the fact Cope's original Coelophysis material can't be assumed to be a single taxon.  We now have Coelophysis bauri (cervical AMNH 2701), Eucoelophysis baldwini (femur AMNH 2704), Shuvosauridae (femur AMNH 2725), Dromomeron romeri (femur AMNH 2721- Nesbitt et al., 2009) and Parasuchia (teeth AMNH 2733- Padian, 1986).  Yet it also shows that some of the material IS diagnostic, people just have to bother actually examining it.

That supposedly indeterminate Coelophysis type material

The Kayentavenator study encouraged me to clean up and flesh out the coelophysoid portion of my website.  In doing so, I found something interesting.

By now, everyone knows the history of Coelophysis.  Cope based the genus on a collection of disarticulated elements found in 1881, but in 1947 the famous Ghost Ranch* bonebed of hundreds of specimens was found, which Colbert referred to Coelophysis.  Since then, the Ghost Ranch specimens have formed the basis for our understanding of Coelophysis bauri.  Hunt and Lucas (1991) stated Cope's material is indeterminate and created the new taxon Rioarribasaurus colberti for the Ghost Ranch taxon.  Colbert et al. (1992) petitioned the ICZN to make a Ghost Ranch specimen the neotype of Coelophysis, which was accepted by the ICZN in 1996.

* Why is this now being called the Whitaker quarry, by the way?  It seems pointless to rename such a well known locality.

Now Cope's Coelophysis material was referred to three species, C. longicollis, C. bauri and C. willistoni.  Hay (1930) designated bauri as the type species without comment.  After a flawed attempt by Welles (1984), Colbert (1989 for C. bauri) and Hunt and Lucas (1991 for C. longicollis and C. willistoni) were the first to actually designate lectotype specimens from Cope's syntypes.  C. longicollis' lectotype is the cervical vertebra AMNH 2701.  Hunt and Lucas state-

"The lectotype of C. longicollis is not diagnostic beyond the level of a primitive theropod, and we consider the taxon a nomen dubium. In so concluding, we emphasize that whichever of COPE'S syntypes of C. longicollis is chosen, it a nomen dubium, because none of the syntypes are diagnostic."

Lectotype of Coelophysis longicollis (AMNH 2701)- anterior cervical vertebra in lateral (a), ventral (b) and anterior (c) views (after Huene, 1915).  Note anterior pedicular foramen to left of neural canal in c.

Just as with most declared nomina dubia, a brief statement without any comparison is deemed sufficient to make a taxon indeterminate.  Yet anyone who saw AMNH 2701 could note it's certainly not just a primitive theropod.  If nothing else, its elongation is only seen in derived coelophysoids.  Beyond that though, today I noticed it has anterior pedicular foramina.  These are so far only known in Coelophysis bauri, and are absent in "Megapnosaurus" kayentakatae and the Shake-n-Bake coelophysid for instance.  Tykoski (2005) considered them autapomorphic for C. bauri, though he noted the condition in Megapnosaurus is unknown due to the brief description.

Interestingly, C. longicollis was based on more specimens than C. bauri, which were more complete than those of the latter species, was larger, and was described first in Cope's paper.  It could have easily ended up being the type species of Coelophysis if not for Hay's seemingly arbitrary decision.  And in that case, the type of Coelophysis would have been diagnostic after all, making the neotype designation unecessary.  As it is, Coelophysis and its type species bauri are both based on a complete Ghost Ranch skeleton now, so it doesn't even matter if the bauri lectotype (an incomplete sacrum and ilial fragment) are diagnostic.  But longicollis can now be made a synonym of bauri at least with evidence besides the assumption all of Cope's material belonged to one taxon.

Friday, October 1, 2010

Is Kayentavenator a young "Megapnosaurus" kayentakatae?

For the Kayentavenator conclusion, we'll see how it compares to other coelophysoids, and "Megapnosaurus" kayentakatae in particular.

Gay's diagnosis

Gay lists several characters in the diagnosis which are meant to distinguish it from other theropods, including kayentakatae. One of these is the supposed medial accessory femoral condyle discussed in the last post. Another is the acetabular shape, which is described as arching "upward under the acetabular rim, making it taller than it is wide." However, it is clear from the illustration and Tykoski's photo that the supracetabular crest is broken. If it was pendent as in other coelophysoids, the apparent acetabular depth would decrease. If the above speculation about the pubic peduncle being broken in Gay's illustration is correct, this would also add to the acetabulum's length once corrected for.

Left- "Megapnosaurus" kayentakatae partial pelvis in lateral view (after Tykoski, 1998). Above right- Kayentavenator partial ilium in lateral view (after Gay, 2010).  Hypothesized complete ilial peduncle and supracetabular crest dotted in, along with ischium. Below right- Kayentavenator partial ilium in ventral view (after Tykoski, 2005).  Note large ventral surface of pubic peduncle, differing from Gay's drawing.

The greater trochanter and femoral head are stated to be fused, which seems to be an unorthodox way of saying there is no concavity between them. Gay notes in the description Coelophysis shares this morphology, and this is true for all other coelophysoids as well. Gay describes a mediodistal crest on the femur extending from the medial condyle for at least half the length of the element. While this might be assumed to be the medial epicondyle on the anteromedial edge common in non-tetanurines (but always less than a third of femoral length), kayentakatae also has a longer (40% of femoral length) crest extending from the medial condyle on the posterior shaft. Of course if the distal femora have been switched as proposed above, the crest would become lateral instead. A posterior lateral crest is present in kayentakatae's holotype, but this is intermediate in length between the medial epicondyle and postromedial crest. These posterior crests are undeveloped or poorly developed in Dilophosaurus, Liliensternus, Coelophysis and Segisaurus, though seem present in at least some Megapnosaurus. The distal femur is photographed in anterior view and shows no evidence of a medial epicondyle (though the dark coloring in this area could indicate the bone surface is broken off), while any posterior crest is of course unobservable. The transverse groove on the proximal femoral head surface is said to be unique among theropods, but is polymorphic in Coelophysis (e.g. NMMNH P-29046 and P-54620, UCMP 129618), so could be expected in some kayentakatae individuals as well.

The caudal centra are said to be highly constricted, with the description further specifying "minimum width of approximately 4mm, with an articular surface diameter of 17mm (Figure1)." Based on the scale in that figure, the articular surface is indeed close to 17 mm, but the minimum central height is 11 mm instead of 4 mm. While kayentakatae caudals have not been illustrated in lateral view, these proportions are similar to other coelophysoids like Megapnosaurus and Liliensternus.

A few additional characters are listed as being specifically distinct from kayentakatae. The anterior trochanter is said to be placed more medially, but this is not true. It should be noted that only robust femora are otherwise known for kayentakatae, which makes comparison of minor details questionable. The trochanter of Kayentavenator is actually more laterally placed than gracile individuals of Dilophosaurus and Megapnosaurus, but comparable to Liliensternus. The "groove in ventral surface of femoral head" is presumedly a typo for the groove in the proximal surface, which is dealt with above. The "spike on medial surface of tibia" is a typo for the lateral fibular crest, as indicated by Gay using the same character with 'lateral' substituted for 'medial' to distinguish Kayentavenator from Coelophysis, Megapnosaurus and Dilophosaurus. The crest of course is not a spike, and as previously noted is stated to be large in kayentakatae as well.

Thus the supposed diagnostic characters are all problematic. The accessory femoral condyle and acetabular shape may be misinterpreted, the distal femoral crest is unique as described but impossible to homologize, the caudal proportions and "fused" greater trochanter are normal for coelophysoids, and the transverse femoral head groove is prone to individual variation.

Is Kayentavenator distinct from other coelophysoids?

Comparing Kayentavenator to other coelophysoids is made difficult not only by the poor preservation and juvenile status of the former, but also the wanting description and figures, as well as the general lack of postcranial characters in coelophysid diagnoses. The one complete caudal centrum of Kayentavenator lacks a ventral median groove, unlike at least some of kayantakatae's centra. Yet this varies within the tail of many theropods like Eustreptospondylus, so is probably unimportant. The pubic peduncle being longer than wide is more similar to Megapnosaurus than Dilophosaurus and Liliensternus, as is the narrow and ventrally pointed ischial peduncle. The femoral head is more elongate than other coelophysoids (including Halticosaurus- contra Gay), but this shows individual variation that could be accommodated by kayentakatae as noted in the last post. If Gay's correct about the anterodistal femoral fossa, this is like Megapnosaurus, Segisaurus and kayentakatae but unlike Coelophysis, Liliensternus and Dilophosaurus. The fibular crest is larger in Segisaurus than in Coelophysis, which is in turn larger than in Dilophosaurus. Based on Gay's description, Kayentavenator is more similar to coelophysids in this respect, but without figures it's difficult to determine. Similarly, any comparisons of vertebral fossae or distal femoral ridges are hindered by their unknown homology due to a lack of description and figures.

Based on published evidence, Kayentavenator seems to be a coelophysid. Past that, it's difficult to tell. There's nothing verified that is more similar to kayentakatae than to other coelophysids, so I don't think it should be referred to that species. There are already at least two Kayenta coelophysids after all (kayentakatae and the Shake-n-Bake taxon which is too small and fused to belong to Kayentavenator). There are a few supposed diagnostic characters that have escaped definite rejection (short anteriorly projected pubic peduncle on the ilium; accessory medial femoral condyle; ambiguous mediodistal femoral crest longer than half of shaft length), but I'm hesitant to believe these are real based on the lack of appropriate femur illustrations, differences from the ilium's photo in Tykoski's thesis, and generally large amount of errors present in the paper. Further analysis may vindicate Gay or may identify features shared only with kayentakatae. At the moment, whether one makes Kayentavenator a nomen dubium depends on how much one trusts Gay's description.

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

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

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