Monday, May 26, 2014

Is Thecocoelurus an ornithomimosaur?

Allain et al. (2014) recently claimed Thecocoelurus, a small partial theropod cervical vertebra from Early Cretaceous England, is "morphologically identical" to an undescribed supposed ornithomimosaur from the Early Cretaceous of France (from here on called the Angeac taxon).  After reading Andrea Cau's post on the topic, I decided to do some in depth comparison.

Besides the Angeac taxon, Thecocoelurus has been compared to several taxa with surprisingly similar cervical vertebrae- caenagnathids (Naish et al., 2001; Naish and Martill, 2002); Falcarius (Kirkland et al., 2004; Zanno, 2010a); and noasaurids (Naish, 2011).  These all have elongate amphicoelous cervicals with low neural spines, anterior peduncular fossae, two pairs of pleurocoels and a transversely concave ventral surface defined by lateral ridges confluent with the parapophyses.  Which is most similar to Thecocoelurus?

Naish et al. (2001) and Naish and Martill (2002) both argue it is closer to oviraptorosaurs than to therizinosauroids based on the rounded pleurocoel and thin neural spine, but this is also the case in basal therizinosaurs (Falcarius, Jianchangosaurus) (as noted by Zanno, 2010a) and noasaurids. Naish (2011) on the other hand, felt "the idea that large caenagnathids were present in Western Europe during the Barremian is difficult to reconcile with what we know of oviraptorosaur biogeography and distribution", thus favored an abelisauroid identity (I suppose based on Genusaurus).  I'd argue basal oviraptorosaurs could and do have similar morphologies (e.g. the Early Cretaceous Similicaudipteryx) and that small theropod diversity in Cretaceous Europe is very poorly known. 

Allain et al. make two new comparative arguments for Thecocoelurus being closest to the Angeac taxon.
1. They distinguished both from Noasaurus based on their concave anterior central surface, but this is true in Masiakasaurus as well. It is also true of all coelurosaurs being compared.
2. They also paired Thecocoelurus with the Angeac taxon based on pneumatic foramina above the prezygapophyses which invade the neural arch. Yet these are present in cervicals 6-10 of Masiakasaurus (Allain et al. state they are "in a modified form" but don't elaborate), at least cervical 9 of Heyuannia, and in Conchoraptor and "Ingenia" (Lu, 2004; contra Allain et al.'s claim they are unknown in oviraptorosaurs). They are also only present on the left side of Thecocoelurus (pf? in figure below, lower left), further posterior than in at least Masiakasaurus and the Angeac taxon, perhaps suggesting breakage of a naturally hollow area or pneumatic asymmetry. The only preserved posterior cervical of Falcarius doesn't preserve this area, nor does the illustrated and best preserved cervical of Chirostenotes.

So let's compare!  Contra Naish and Martill, the specimen resembles posterior cervicals more than anterior ones, and indeed the supposedly identical Angeac vertebra matches the seventh or eighth of Harpymimus based on elongation, central articular surface orientation, prezygapophyseal length and orientation, etc. (contra Allain et al.).

Anterior half of posterior cervical vertebrae in (descending) right lateral, anterior, ventral and dorsal views.  From left to right- Thecocoelurus holotype (after Naish and Martill, 2002); Angeac taxon ANG 10/175 (after Allain et al., 2014); Falcarius UMNH VP 14657 (after Zanno, 2010b); Masiakasaurus FMNH PR 2481 (after Carrano et al., 2011); Chirostenotes or Epichirostenotes ROM 43250 (after Sues, 1997); Similicaudipteryx holotype (after He et al., 2008).

The elongate parapophyses resemble Falcarius, Chirostenotes and Similicaudipteryx more than Masiakasaurus or the Angeac taxon.
The anterior pleurocoels are placed in an obvious fossa, like Falcarius and the Angeac taxon, but unlike Masiakasaurus, Chirostenotes or Similicaudipteryx.
The infradiapophyseal fossa is developed as an elongate groove, as in Falcarius but unlike Masiakasaurus, the Angeac taxon, Chirostenotes or Similicaudipteryx.
The centrum is taller than wide (midline height / width minus parapophyses 133%) as in Falcarius (118%), but unlike the Angeac taxon (95%) and especially Chirostenotes (74%) and Masiakasaurus (64%).
The anterior peduncular fossae are well defined as in Chirostenotes and at least anterior Falcarius cervicals, but unlike Masiakasaurus or the Angeac taxon. They are however also well defined in anterior Masiakasaurus cervicals, so the condition in Falcarius isn't necessarily better than that genus or the Angeac taxon.
They are also placed far below the diagonal prezygapophyseal surface as in at least anterior Falcarius cervicals, but unlike the Angeac taxon, Chirostenotes or Masiakasaurus. The same could be said re: anterior Masiakasaurus cervicals.
The prespinal fossa is broad like Chirostenotes and Masiakasaurus but unlike the Angeac taxon.
It has anteroposteriorly broad exposure dorsally as in the Angeac taxon and at least anterior Falcarius cervicals, but not Masiakasaurus (including anterior cervicals of the latter).

Overall, Thecocoelurus is most similar to Falcarius and least similar to Masiakasaurus.  There are four good characters shared with Falcarius to the exclusion of the Angeac taxon, and three characters that are more similar to Chirostenotes than to the Angeac taxon, but two characters that are more similar to the Angeac taxon than to Chirostenotes.

Thecocoelurus holotype completed with the posterior of Falcarius (modified from Naish and Martill, 2002 and Zanno, 2010).  This results in a centrum length of 68 mm for Thecocoelurus, compared to Naish's (2011) estimate of 70-90 mm.

Falcarius does differ from Thecocoelurus in having a ventral median ridge on its centra, but this is an autapomorphy not seen in other therizinosaurs.  Besides this, no characters differ between the specimen except exact size and shape of pneumatic features, which themselves vary between right and left sides of Thecocoelurus.  Both are Barremian, and Thecocoelurus is 58% the size of the Falcarius individual that preserved the posterior cervical (though a growth series is known, where that individual falls is unreported).  Whether Thecocoelurus and Falcarius share derived characters to the exclusion of other therizinosaurs would require more study, but at the moment is seems most parsimonious to consider Thecocoelurus a basal therizinosaur and not closely related to the Angeac taxon.

References- Sues, 1997. On Chirostenotes, a Late Cretaceous oviraptorosaur (Dinosauria: Theropoda) from Western North America. Journal of Vertebrate Paleontology. 17(4), 698-716.

Naish, Hutt and Martill, 2001. Saurichian dinosaurs 2: Theropods. In Martill and Naish (Eds). Dinosaurs of the Isle of Wight. The Palaeontological Association. 242-309.

Naish and Martill, 2002. A reappraisal of Thecocoelurus daviesi (Dinosauria: Theropoda) from the Early Cretaceous of the Isle of Wight. Proceedings of the Geologists’ Association. 113, 23-30.

Kirkland, Zanno, DeBlieux, Smith and Sampson, 2004. A new, basal-most therizinosauroid (Theropoda: Maniraptora) from Utah demonstrates a Pan-Laurasian distribution for Early Cretaceous therizinosauroids. Journal of Vertebrate Paleontology. 24(3), 25-26.

Lu, 2004. Oviraptorid dinosaurs from Southern China. PhD Thesis. Southern Methodist University. 249 pp.

He, Wang and Zhou, 2008. A new genus and species of caudipterid dinosaur from the Lower Cretaceous Jiufotang Formation of Western Liaoning, China. Vertebrata PalAsiatica. 46(3), 178-189.

Zanno, 2010a. A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora). Journal of Systematic Palaeontology. 8(4), 503-543.

Zanno, 2010b. Osteology of Falcarius utahensis: Characterizing the anatomy of basal therizinosaurs. Zoological Journal of the Linnaean Society. 158, 196-230.

Carrano, Loewen and Sertich, 2011. New materials of Masiakasaurus knopfleri Sampson, Carrano, and Forster, 2001, and implications for the morphology of the Noasauridae (Theropoda: Ceratosauria). Smithsonian Contributions to Paleobiology. 95, 53 pp.

Naish, 2011. Theropod dinosaurs. In Batten (ed.). English Wealden Fossils. The Palaeontological Association. 526-559.

Allain, Vullo, Le Loeuff and Tournepiche, 2014. European ornithomimosaurs (Dinosauria, Theropoda): An undetected record. Geologica Acta. 12(2), in press.

Saturday, May 24, 2014

Revisiting a BAND cladogram

Twelve years ago, I replied to a post Nick Gardner wrote to the DML, critiquing and updating the phylogenetic analysis of Hou et al. (1996).  This was perhaps the first analysis that I corrected and reran, which is now the concept behind an entire section of my website.  Well, now I've officially reexamined Hou et al.'s data for an entry in the Database.

To jog everyone's memory, Hou et al.'s paper provided details on Confuciusornis, Liaoningornis and Chaoyangia and was interesting in that it included a cladogram with matrix for birds, not before (or since?) done by the Birds Are Not Dinosaurs (BAND) crowd.  This cladogram supported the BAND concept of Sauriurae including Confuciusornis and enantiornithines, and supposedly used Petrolacosaurus as an outgroup.  Hou et al. claim "The use of a coelurosaurian dinosaur like Velociraptor as the outgroup would make no difference for character states."  Really?  The figured cladogram also oddly differed from the matrix in  adding 'Modern Birds' as sister to Ichthyornis and replacing Cathayornis with Enantiornithes.  The figure has a similar but different character list than the matrix (note my old post dealt with the figure's character list, so the numbers don't match up with my new critique).  The authors' phylogeny was-
|--outgroup (Petrolacosaurus)
   |  |--Archaeopteryx
   |  `--+--Confuciusornis
   |     `--Cathayornis

Correcting and re-running the matrix

Go here to read commentary on all of the characters and codings.  This analysis is hindered by its small size, several characters based on fictional morphologies, others that are the opposite of other characters, and some which are based on developmental assumptions that cannot be coded in adult specimens. This leaves only seventeen characters that are valid and phylogenetically informative. The anatomy of Archaeopteryx has been greatly misunderstood by BANDits for decades, which spread somewhat to Confuciusornis. Hou et al. also ascribed unsupported referred specimens to Cathayornis and Chaoyangia, negating many of the codings for those taxa. Petrolacosaurus was coded 0 for everything, including characters it actually has state 1 for, those which are unpreserved, and even those based on structures it lacks. Ichthyornis meanwhile was coded as if it were a complete ornithurine, despite not preserving several elements. These examples show Hou et al. coded taxa as idealized hypothetical examples instead of actual specimens. In total, 43% (110/256) of characters were miscoded, though this is somewhat exaggerated by the several deleted characters. Once corrected, the consensus is-

`--Eosuchia to Ornithes
      |  |--Cathayornis
      |  `--Liaoningornis

This differs from the original tree in having a paraphyletic 'Sauriurae', though differs from the modern consensus in placing Confuciusornis closer to Aves than enantiornithines. This is no doubt due to the low number of characters, and as noted on my site, changed with only 2 extra steps. Liaoningornis moved to Enantiornithes, matching O'Connor's (2012) redescription.  Hou et al.'s original flawed matrix finds Pygostylia and Ornithothoraces instead of Sauriurae with only 3 extra steps, so doesn't even support their own hypothesis strongly.  Indeed, my conclusion is that the matrix is too small to strongly reject any proposed hypothesis.

What about Petrolacosaurus?

It's very odd that Hou et al. would choose Petrolacosaurus as their avian outgroup.   I mean, even BANDits think birds are archosaurs, so why not use Euparkeria or Ornithosuchus?  As noted above, they state "The use of a coelurosaurian dinosaur like Velociraptor as the outgroup would make no difference for character states" compared to their supposed use of Petrolacosaurus. Well let's check that.

If Velociraptor is added, there are in fact nine characters that are coded differently. Velociraptor is known to have feathers (based on ulnar quill knobs) whereas Petrolacosaurus' integument is unpreserved though originally miscoded as known.  Petrolacosaurus is inapplicable for hypocleidium length, anterior sternal groove presence and sternal length (all originally miscoded), due to lacking a furcula or ossified sternum, unlike Velociraptor. Velociraptor has uncinate processes, unlike Petrolacosaurus or even Archaeopteryx. Velociraptor has an ectocondylar tuber on its femur like Archaeopteryx, though Hou et al. view the latter's structure as a non-homologous structure. Petrolacosaurus' pedal unguals are not enlarged (again miscoded by Hou et al.), but Velociraptor has pedal ungual II enlarged so is polymorphic. Most amusingly, Petrolacosaurus actually has a dorsolaterally grooved clavicle and proximodorsal ischial process like some basal birds (but unlike Velociraptor), though Hou et al. miscoded these in assuming it was a generic diapsid.  That's right.  The BANDits had data to support their hypothesis, but didn't realize it due to their own laziness and evolutionary assumption that these were derived sauriurine characters instead of symplesiomorphies.

Bird-like characters of Petrolacosaurus assumed to be absent by Hou et al. (1996).  Left- left clavicle in lateral view showing posterolateral groove in pink. Right- left pelvis in lateral view showing proximodorsal ischial process in pink. Both modified after Reisz (1981).
Incidentally, if Velociraptor replaces Petrolacosaurus, the tree is the same except that confuciusornithids, enantiornithines and ornithuromorphs are in a trichotomy, allowing the current consensus.

References- Reisz, 1981. A diapsid reptile from the Pennsylvanian of Kansas. University of Kansas Museum of Natural History. Special Publication 7, 74 pp.

Hou, Martin, Zhou and Feduccia, 1996. Early adaptive radiation of birds: Evidence from fossils from northeastern China. Science. 274, 1164-1167.

Saturday, March 22, 2014

Anzu is no Rosetta Stone (yet?)

Last time I said Aves tests would be my next post, but I didn't know Anzu would be published so soon.  For those out of the loop, Anzu wyliei (Lamanna et al., 2014) is the name given to Triebold's two big Hell Creek caenagnathids, to which are also referred the posterior mandible FMNH PR 2296 (Currie et al.'s 1994 Caenagnathus sp., then catalogued as BHM 2033) and a fragmentary skeleton called Chirostenotes sp. by Schachner et al. (2006).

Caenagnathid taxonomy has been controversial for decades because most species from the Campanian-Maastrichtian are known from parts which don't overlap with others.  Caenagnathus collinsi, C? sternbergi and Leptorhynchos are known from mandibles, Chirostenotes, Hagryphus and Elmisaurus rarus are known from hands, and Macrophalangia, Elmisaurus rarus and E? elegans are known from metatarsi.  In addition, two partial skeletons have been described.  RTMP 79.20.1 preserves a manus and pes but no mandible, and has been agreed by most to be Chirostenotes.  ROM 43250 doesn't preserve mandibles, manus or pes, and has been called Epichirostenotes.  I don't think it differs significantly from Chirostenotes (RTMP 79.20.1 shares the sacrum, ischium and distal tibia), but its later age means it probably was different.  I've been hoping Anzu would be the Rosetta Stone for caenagnathids, since it preserves mandibles, manual material and pedal material, along with sacrum, ischium and tibia.  Alas, at least with the info provided by Lamanna et al., it doesn't seem to help much.

My first inclination was to check the phylogenetic analysis.  The authors did an excellent job sampling basically all oviraptorosaurs and adding characters from the various oviraptorosaur analyses that began back with Maryanska et al. (2002).  Though I do wonder where Protarchaeopteryx is and why the complete Similicaudipteryx specimens weren't coded.  Note the much younger Yulong was included, the poorly illustrated Jiangxisaurus, and the barely codable Ojoraptorsaurus, so none of those seem like reasonable excuses.  It probably explains why Similicaudipteryx ends up in Caudipteridae, since the holotype doesn't preserve the skull or manus.  Also note Lamanna et al. use the incorrect Caudipterygidae instead of Caudipteridae.  In any case, Caenagnathidae is a big polytomy in Lamanna et al.'s strict consensus tree, which is unsurprising if for no other reason than they included Ojoraptorsaurus, a dubious taxon known from an incomplete pubis and only codable for three characters.  The authors then include only caenagnathids known from dentary material and find the same topology as in the Leptorhynchos paper.

But surely Anzu could help us do more?  What about including only caenagnathids known from manual material (Chirostenotes, Elmisaurus, Hagryphus, Anzu)?  Only pelvic material (Chirostenotes, Epichirostenotes, Anzu)?  Only pedal material (Chirostenotes, Macrophalangia, Elmisaurus)?  The authors don't test these, so I did.  And they're all polytomies. I even gave intertaxon overlap its best chance by combining probably synonymous taxa like Longrich et al. (2013), so that collinsi and Macrophalangia are one, Chirostenotes and sternbergi are one, and Elmisaurus/Leptorhynchus is one OTU.  But still, no resolution*.

* The one exception is the pelvic test, where Epichirostenotes is closer to Anzu than Chirostenotes (RTMP 79.20.1).  Alas, this is based on one character, the ventral flange on the pubic peduncle of the ischium, supposedly lacking in the latter.  Going back to the original description of RTMP 79.20.1 by Currie and Russell (1988), they state "The proximal end of the ischium is crushed, so that the iliac and pubic sutures cannot be distinguished" and their figure shows that area with a different texture and irregular outline, suggesting the lack of a flange is taphonomic.  Even if it wasn't, Tyrannosaurus, Microraptor and Archaeopteryx all vary in this character.

Gigantoraptor on the left (after Xu et al., 2007), Anzu on the right (after Lamanna et al., 2014).  Which one is the main postcranial figure from a Nature publication, and which is from a PLoS ONE publication?

So it seems the matrix just doesn't have the characters to distinguish Campanian-Maastrichtian caenagnathids.  But we can compare Anzu to the other taxa ourselves, right?  Well, kinda.  This is my biggest complaint about the paper, namely that illustration- and description-wise, it might as well be in Science or Nature.  The illustrations are gorgeous, don't get me wrong, but there are so few of them.  A total of 20 postcranial elements are illustrated (only 6 in more than one view), out of 31 preserved kinds of appendicular elements and 47 vertebral elements, plus ribs, chevrons and gastralia.  Sure illustrations take time, but what about photographs?  This is PLoS ONE- there's no limit to the number of figures that can be included.  The description is similarly lacking.  This is the first uncontroversial caenagnathid to preserve a scapula, radius, ulna or fibula, but each of these elements gets only one sentence of description and the fibula isn't even illustrated outside the line drawing skeletal reconstruction.  The measurement tables are also only partially complete.  We have the first complete presacral series for a caenagnathid and a tail three-fourths complete, but only three cervicals, two dorsals of unstated position and the three distalmost caudals are measured.  Even the materials list is vague.  The holotype includes "multiple cervical and caudal vertebrae", "several
manual phalanges including unguals" and "several pedal phalanges including unguals", while CMN 78001 includes "several caudal vertebrae" and "several pedal phalanges including unguals".  Why not just be exact?  You can get a bit of this information from the measurement table, but not all of it since only some bones are measured.

All of this combines to make it very difficult to improve caenagnathid taxonomy using Lamanna et al. (2014).  Want to compare the manus to Chirostenotes, Hagryphus and Elmisaurus rarus?  You get three sentences, a drawing of ungual I in one view and measurements of five bones.  Want to compare the sacrum to Chirostenotes and Epichirostenotes?  You get two sentences and three measurements.  Compare the pes to Macrophalangia, Chirostenotes and Elmisaurus?  One sentence, a drawing of an unidentified pedal ungual in one view, and the length of nine bones.  There's just very little to work with, so that the status of Anzu has changed remarkably little with its official publication.  It remains important in theory, but with too little information released to work with much in practice.  Hopefully, this is only a preliminary description that will be supplemented by a monograph in the future.

References- Currie and Russell, 1988. Osteology and relationships of Chirostenotes pergracilis (Saurischia, Theropoda) from the Judith River (Oldman) Formation of Alberta, Canada. Canadian Journal of Earth Sciences. 25, 972-986.

Currie, Godfrey and Nessov, 1994. New caenagnathid (Dinosauria: Theropoda) specimens from the Upper Cretaceous of North America and Asia. Canadian Journal of Earth Sciences. 30(10), 2255-2272.

Maryanska, Osmolska and Wolsan, 2002. Avialan status for Oviraptorosauria. Acta Palaeontologica Polonica. 47 (1), 97-116. 

Schachner, Lyson and Hanks, 2006. A preliminary report of a new specimen of Chirostenotes (Oviraptorosauria: Theropoda) from the Hell Creek Formation of North Dakota. Journal of Vertebrate Paleontology. 26, 120A.

Xu, Tan, Wang, Zhao and Tan, 2007. A gigantic bird-like dinosaur from the Late Cretaceous of China. Nature. 844-847.

Lamanna, Sues, Schachner and Lyson, 2014. A new large-bodied oviraptorosaurian theropod dinosaur from the Latest Cretaceous of Western North America. PLoS ONE. 9(3), e92022.

Tuesday, March 11, 2014

Theropod Database info published and credited

I've done my fair share of complaining when material of mine is published without attribution, or ideas suspiciously similar to mine are published.  But there's the flipside as well- when authors credit me in their work, and this post is a thanks to them.

Most recently, Hendrickx and Mateus (2014b) in their description of Torvosaurus gurneyi not only credited me for photos and Dilophosaurus "breedorum" info, they even linked to my blog in the supplementary info.  Thank you so much.

Similarly, Hendrickx and Mateus (2014a) credited me in their theropod tooth paper.  I was very happy to see my hypothesis Richardoestesia is a dromaeosaurid supported by their analysis.

There's also Soto and Perea (2008) on ceratosaurid teeth, Martyniuk (2012) for a lot of things in his field guide as mentioned before, and Zanno and Makovicky (2013) on theropod herbivory.  Thanks everyone.

Coming up... Aves tests.

References- Soto and Perea, 2008. A ceratosaurid (Dinosauria, Theropoda) from the Late Jurassic-Early Cretaceous of Uruguay. Journal of Vertebrate Paleontology. 28(2), 439-444.

Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Zanno and Makovicky, 2013. No evidence for directional evolution of body mass in herbivorous theropod dinosaurs. Proceedings of the Royal Society B: Biological Sciences. 280(1751), 20122526.

Hendrickx and Mateus, 2014. Abelisauridae (Dinosauria: Theropoda) from the Late Jurassic of Portugal and dentition-based phylogeny as a contribution for the identification of isolated theropod teeth. Zootaxa. 3759(1), 1-74. 

Hendrickx and Mateus, 2014b.  Torvosaurus gurneyi n. sp., the largest terrestrial predator from Europe, and a proposed terminology of the maxilla anatomy in nonavian theropods. PLoS ONE. 9(3), e88905.

Saturday, March 8, 2014

Testing pterosaur origins in Ezcurra et al. (2014)

There's a new amniote analysis out from Ezcurra et al. (2014) emphasizing the lepidosauromorph-archosauromorph split.  Thev changed a ton of codings from the earlier version by Reisz et al. (2010), almost doubled the size of the matrix, properly ordered most characters, made sure inapplicable codings stopped redundancy in most cases, AND got rid of suprageneric OTUs.  Among the negative points are no parareptiles or aquatic diapsids (yet many synapsids) and a lack of many of the traditional series-based characters (e.g. number of phalanges on digit X, number of vertebrae in this segment).  Regardless, this seems to be better than most amniote analyses, and the lepidosauromorph-archosauromorph split is the perfect place to test pterosaur origins.

Among relevant taxa, the matrix has Peters' closest consensus lepidosaur to pterosaurs, Huehuecuetzpalli, plus two more squamates.  It has Macrocnemus, placed even closer to pterosaurs by him, plus three more protorosaurs.  Also Euparkeria and Erythrosuchus for the Bennett hypothesis.  I added two pterosaurs from the basalmost clade (Preondactylus and Eudimorphodon), Megalancosaurus, Longisquama and Eoraptor.  Note this is far from perfect, as incomplete basal dinosauromorphs (lagerpetonids, Marasuchus), more basal simiosaurs (Vallesaurus, Hypuronector), and more derived pterosaurs with well preserved braincases, palates and axial details would all be useful to add.  Not to mention Scleromochlus, Sharovipteryx, Cosesaurus and Atanassov's taxa.  But what does this preliminary test find?

The pterosaurs were closest to Megalancosaurus, but this clade was sister to Eoraptor within Archosauriformes.  No pseudosuchians were included, so it's uncertain if pterosaurs are strictly archosaurs.  What about Longisquama?  Either a tanystropheid protorosaur or a member of the megalancosaur-pterosaur clade, though note I did (conservatively) use Peters' (2000) illustration for the anatomy.  This may bias it toward those interpretations, though his interpretations were far less fanciful back then.

Forcing pterosaurs to be protorosaurs is 9 more steps, so rather unlikely.  Forcing them to be lepidosauromorphs is 17 more steps though, so probably wrong.

Forcing Megalancosaurus to be an archosauriform outside Ornithodira is only two steps longer, so about equally likely.   The same number of steps move it to Tanystropheidae, with Longisquama following, but not pterosaurs.

Forcing Longisquama to be a lepidosauromorph only takes two steps, and it becomes the most basal one.  Forcing it to be sister to Coelurosauravus results in both being basal lepidosauromorphs, which only takes 3 more steps.  Having this pairing outside Sauria as in Senter (2004) is 5 more steps, so less likely.  Adding Megalancosaurus to complete Senter's Avicephala is 9 more steps though, so rather unlikely.

Finally, enforcing Peters' versions of Lepidosauromorpha (with captorhinids, caseids, weigeltisaurids, trilophosaurs, rhynchosaurs, simiosaurs, Longisquama, tanystropheids and pterosaurs) and Archosauromorpha (with derived synapsids, Paleothyris, araeoscelids and younginiforms) takes a whopping 75 extra steps.  This is worse than any alternative phylogeny I've ever tested for anything.

Instead of asking what pterosaurs are, maybe we should be asking if simiosaurs belong in Archosauria.  Recall even in Nesbitt's (2011) huge analysis focusing on archosaur interrelationships, they could be placed in Avemetatarsalia with only five extra steps.  At the time I thought a broader analysis would be more useful for that question, but here they flit between Archosauriformes and Protorosauria with even less difficulty.  Longisquama is pretty clearly too poorly described to strongly favor any alternative, but it's interesting that Senter's placement for it comes out as badly as it does.  As for what pterosaurs are, while archosauriform beats out protorosaur and both beat out lepidosauromorph, I've seen taxa recover from a 9 step disadvantage often, and a 17 step disadvantage rarely, so both of the latter alternatives are still possible.  75 steps?  Not so much.

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

Reisz, Laurin and Marjanovic, 2010. Apsisaurus witteri from the Lower Permian of Texas: Yet another small varanopid synapsid, not a diapsid. Journal of Vertebrate Paleontology. 30, 1628-1631.

Ezcurra, Scheyer and Butler, 2014. The origin and early evolution of Sauria: Reassessing the Permian saurian fossil record and the timing of the crocodile-lizard divergence. PLoS ONE. 9(2), e89165.

Friday, February 28, 2014

Remember Teyuwasu?

Way back in the days of yore, I had DML post style called "Details on..." where I would report information about obscure dinosaur taxa.  This was before the modern methods of organized file exchange, so to learn more about a newly reported taxon, you'd generally have to request a paper copy from Tracy Ford.  We were all pretty clueless, so I hoped to spread some knowledge around.  One of my posts from 2000 was "Details on Teyuwasu"*, an enigmatic dinosaur described briefly in an abstract and based on  bones first described in an old German paper that was even harder to acquire.  It seems online information on Teyuwasu is still hard to find, so here's an update 14 years later.

* Btw, while I interpreted Kischlat's statement "the distal process is so developed as to encompass the ascending process of astragalus" as being similar to coelophysoids' anterior overlap, it's actually the posterolateral process extending laterally a bit behind the ascending process as in most dinosauriforms.  Hooray for imprecise translations.

Teyuwasu Kischlat, 1999 vide Kischlat, 2000
= "Teyuwasu" Kischlat, 1999
T. barberenai Kischlat, 1999 vide Kischlat, 2000
= "Teyuwasu barberenai" Kischlat, 1999
Late Carnian-Early Norian, Late Triassic
Alemoa Member of Santa Maria Formation, Brazil
- (BSPG AS XXV 53) femur (276 mm)
....(BSPG AS XXV 54) tibia (264 mm)
?...(BSPG AS XXV 56-59) dorsal centrum (40 mm), partial ilium, (?) distal ischium, femur
Diagnosis- (proposed) extremely robust femur and tibia (minimum transverse femoral width 19% of length); mound-like fourth trochanter.

A-F: Holotype femur BSPG AS XXV 53 of Teyuwasu barberenai in anterior, medial, posterior, lateral, proximal and distal views respectively. G-L: Holotype tibia BSPG AS XXV 54 in proximal, distal, anterior, medial, posterior and lateral views respectively.  Scale = 100 mm. (after Ezcurra, 2012)

Comments- The material was originally described by Huene (1938) as possibly belonging to his new taxon Hoplitosaurus raui, from slightly higher in the formation. Huene later (1942) renamed it Hoplitosuchus, as Hoplitosaurus was preoccupied by an ankylosaur. The taxon was based on two supposed osteoderms described as aetosaurian, but more recently these have been found to be unidentifiable bones by Kischlat (2000) and Desojo and Rauhut (2008). Kischlat (1999) reinterpreted the femur and tibia as being dinosaurian, though only listed features identifying it to the level of Dinosauriformes. He provided a very brief description and named the taxon Teyuwasu barberenai, but as the publication is a symposium abstract, it is invalid under the ICZN (Article 9.10). Kischlat's (2000) later article has similar information, credits the name to the 1999 paper, but is a valid publication. Ezcurra (2012) described the material in depth, finding it certainly belongs to the silesaurid+dinosaur clade, but that the only dinosaurian character is the inturned femoral head. As the bones have been heavily altered taphonomically, Ezcurra was uncertain if the femoral head orientation was artificial. He notes Kischlat's "two paralell ridges running proximodistally" are fractures formed when the medial femoral head was sheared distally. While Ezcurra declared Teyuwasu to be indeterminate, the robusticty itself is vastly different from other basal dinosauriforms, so should be enough to validate the taxon. If added to the Nesbitt archosaur matrix along with all later published additions (including Nyasasaurus and Saltopus), Teyuwasu emerges as a saurischian based on femur longer or about the same length as the tibia, and medial articular facet of the proximal femur rounded.  It's outside Eusaurischia based on the femoral head being unexpanded, symmetrical fourth trochanter (considered tentative by Ezcurra), cnemial crest not laterally curved, and posterior face of distal tibia without longitudinal ridge.  Some of these characters vary within basal saurischians, which are incompletely sampled by Nesbitt, so I wouldn't bet on a non-eusaurischian identity being most parsinomious once all data are in.  Additionally, the coding indicates the moundlike fourth trochanter is unique among sampled ornithodirans, making this another diagnostic character.

Besides the femur and tibia, Huene referred additional material to this individual. A centrum identified by Kischlat (2000) as dorsal was stated by Huene to be possibly but not certainly referrable to this specimen. It is 40 mm long, 45 mm tall and wide, rounded in section and barely amphicoelous to amphiplatyan. A ventral ilium was considered very likely to belong to this individual. It has a supracetabular crest and 'strongly recessed' acetabulum, and narrows to 70 mm between the peduncles and blade. An element tentatively identified by Huene as a distal ischium is much too large to belong to this individual, with the distal end 90 mm deep and 60 mm wide. At the proximal break, these dimensions are 53 and 30 mm respectively. The distal end is triangular in section, which is a saurischian character. Finally, Kischlat (2000) mentioned an additional femur which was not noted by Huene. These were all noted by Kischlat as supplementary material for Teyuwasu, though Desojo and Rauhut stated referred Hoplitosuchus material belongs to Rauisuchia and Dinosauria. The centrum, ilium and/or ischium may comprise the 'rauisuchian' material, or this may refer to the two non-avemetatarsalian calcanea also referred to Hoplitosuchus by Huene.

References- Huene, 1938. Ein grosser Stagonolepid aus der jungeren Trias Ostafrikas. Neues Jahrbuch fur Mineralogie, Geologie und Palaontologie. 80(2), 264-278.

Huene, 1942. Die fossilen Reptilien des sudamerikanischen Gondwanalandes. Ergebnisse der Sauriergrabungen in Sudbrasilien 1928/29. Munich: Becksche Verlegbuchhandlung. 332 pp.

Kischlat, 1999. A new dinosaurian "rescued" from the Brazilian Triassic: Teyuwasu barbarenai, new taxon. Paleontologia em Destaque, Boletim Informativo da Sociedade Brasileira de Paleontologia. 14(26), 58.

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

Desojo and Rauhut, 2008. New insights on "rauisuchian" taxa (Archosauria: Crurotarsi) from Brazil. SVPCA 2008 Programme and Abstracts. 18-19.

Ezcurra, 2012. Comments on the taxonomic diversity and paleobiogeography of the earliest known dinosaur assemblages (Late Carnian-Earliest Norian). Historia Natural. 2(1), 49-71.

Saturday, February 22, 2014

What is Eoraptor revisited 1 - Outside Eusaurischia?

You all know the big Eoraptor monograph was finally published as Sereno et al. (2013) containing the first detailed description of the material.  It may have taken 22(!) years from discovery to publication, but it's an excellent paper.  I previously examined the evidence Martinez et al. (2011) provided for Eoraptor being a sauropodomorph when they announced the idea in their Eodromaeus paper.  I found numerous coding issues and errors, such as composite codings and miscodings, which when partially corrected recovered a theropod Eoraptor instead, and also noted few of the proposed theropod characters had been included in their matrix.

Since then, we have the new basal theropod Daemonosaurus, redescriptions of basal sauropodomorphs Chromogisaurus and Pantydraco, redescriptions of all heterodontosaurids, redescriptions of the near/basal-dinosaurs Saltopus and Nyasasaurus, a version of Yates' analysis finding Eoraptor to be a sauropodomorph and more characters from Nesbitt's and Ezcurra's analyses finding it to be a theropod closer to Avepoda than herrerasaurids.  So let's explore the suggested evidence for each position for Eoraptor.  I'll list all novel suggested characters from each analysis, bolding the ones that seem valid.

Outside Eusaurischia (Sauropodomorpha+Theropoda)

 Padian et al. (1999)
1. centra of posterior cervical vertebrae (6-8) subequal in length to those of anterior dorsal vertebrae (refined by Langer, 2004).  This is untrue in Eoraptor, as cervicals 6-8 are 18-23 mm and the anterior dorsals are 16-17 mm.
2. third finger of the manus longer than second finger.  As this is true in Eodromaeus and Tawa, the opposite condition in known sauropodomorphs and avepods is probably convergent.  Herrerasaurus  also has III longer than II, while Guaibasaurus is like sauropodomorphs and avepods.  Though Tianyulong has an avepod-like condition, Heterodontosaurus and derived ornithischians have III longest, so this was more likely the basal condition in Ornithischia.
3. metatarsal I contacts tarsus.  Since this is also true in Sauropodomorpha, the authors had no reason to list it.  It only excludes Eoraptor from Avepoda.

Langer (2004)
4. subnarial premaxillary process extends posteriorly to the external naris.  This is also true in Daemonosaurus, making the basal condition for Theropoda ambiguous.  As Herrerasaurus has this state as well, it's even worse if herrerasaurids are theropods.
5. radius more than 80% of humerus length.  This is untrue in Eoraptor, which has a ratio of 74%.
6. manual ungual I shorter than metacarpal I.  This is untrue in Eoraptor, which has a ratio of 100%.  Note even if the ratio is actually barely in agreement, Eodromaeus and Tawa have short unguals I too, so it would be another character convergent in avepods and sauropodomorphs.
7. metacarpal III longer than metacarpal II.  Another character also present in Eodromaeus and Tawa, again making sauropodomorphs and avepods convergent. As with the digit length comparison, Guaibasaurus has longer II while Herrerasaurus has longer III.  Also while heterodontosaurids have longer II, other ornithischians and Saltopus have longer III, suggesting the former is convergence.
8. distal end of ischium unexpanded. This is untrue in Eoraptor.
9. medial margin of distal tibia not broader than lateral margin. This is untrue in Eoraptor.

Smith et al. (2007)
10. maxillary tooth count 12-18. Eoraptor has 17, while basal theropods have (9/10)-11 and basal sauropodomorphs don't preserve the area or have unreported counts.  As Saturnalia and Panphagia have 17 and 23 dentary teeth respectively, their maxillary counts were probably within the 12-18 range or higher, not lower as in basal theropods. Thus there is no shared derived state to differ from.
EDIT: Ugh, how could I forget Pampadromaeus?!  It has at least twenty maxillary teeth, proving my point.
11. lateral surface of anterior end of nasal along the posterior margin of the external naris flat.  Pantydraco and Daemonosaurus also lack this narial fossa, though Panphagia has it.  This means Theropoda is basally ambiguous while Sauropodomorpha is barely basally derived in having the fossa, so the character is not an unambiguous eusaurischian synapomorphy.  For what it's worth, Herrerasaurus also lacks the fossa.
12. posteroventral dentary process far posterior to posterodorsal process.  This is true in basal sauropodomorphs  (Panphagia, Pantydraco) and basal theropods (Eodromaeus, Tawa).  It's not true in ornithischians (Tianyulong, Heterodontosaurus, Eocursor) though, making the condition in Saurischia's outgroup ambiguous (given Silesaurus having the opposite condition).  Again for what it's worth, Herrerasaurus has the same condition as ornithischians.
13. foramen in the ventral part of the splenial absent.  This is difficult to code as the anterior splenial is thin and often broken.  In Sauropodomorpha, Panphagia has a foramen, Lamplughsaura is illustrated without one (though by Chatterjee, whose drawings are often idealized), Plateosaurus is polymorphic, and Lufengosaurus and Adeopapposaurus have it.  In Theropoda, Liliensternus lacks one, Dilophosaurus is illustrated as lacking one but seems to be anteriorly incomplete, and Ceratosaurus has one.  Thus the basal condition in either saurischian clade is unclear though more probably present in sauropodomorphs.  Ornithischians lack the foramen, as does Staurikosaurus though the latter has a poorly preserved mandible.
14. iliac supraacetabular crest shelf-like and short, extending primarily laterally.  This is also true in basal sauropodmorphs (Panphagia, Pampadromaeus) and basal theropods (Eodromaeus, Tawa).
15. ridge on lateral side of tibia for connection with fibula absent. This is untrue in Eoraptor

Yates (2007)
16. relationship between posterolateral process of the premaxilla and the anteroventral process of the nasal a broad sutured contact.  This is untrue in Eoraptor.
17. size and position of subnarial foramen small (no larger than adjacent maxillary neurovascular foramina) and positioned outside of narial fossa.  Basal theropods (Tawa, coelophysids, Dilophosaurus) lack a subnarial foramen, as do outgroups (ornithischians, Silesaurus).  Thus there is no obvious ancestral condition for the subnarial foramen, nor evidence theropods ancestrally had one.  Herrerasaurus does have this condition.
18. pointed posterolateral process of the nasal overlapping the lacrimal absent. This is untrue in Eoraptor.
19. length of middle to posterior cervical centra (6-8) no more than the length of the axial centrum. This is unknown in Eoraptor, as the axis is fragmentary.
20. laminae bounding triangular infradiapophyseal fossae on dorsal neural arches absent. This is untrue in Eoraptor.
21. transverse width of the first distal carpal less than 120% of the transverse width of the second distal carpal. This is unknown or untrue in Eoraptor, as distal carpal I is either unpreserved or diagenetically fused to the radiale in the left carpus and ~192% the width of distal carpal II. Notably, the basal theropods Eodromaeus and Tawa and basal sauropodomorph Efraasia have a small distal carpal I though, so this is not a eusaurischian character, though Heterodontosaurus does have a large distal carpal I so that ornithischians have an ambiguous basal state. Herrerasaurus has a small distal carpal I.

Martinez and Alcober (2009)
22. no caudosacral.  This is also true in basal theropods (Eodromaeus and Tawa) and ambiguous in sauropodomorphs (true in Pampadromaeus but not Efraasia and more derived taxa).  Guaibasaurus, Sanjuansaurus and Herrerasaurus also lack a caudosacral, though Staurikosaurus may have one.  Ornithischians have a caudosacral.
23. width of metacarpal I shaft less than 35% of length. This is untrue in Eoraptor.

Bittencourt Rodrigues (2010) also placed Eoraptor basal to Eusaurischia, but this paper has yet to be translated.

What's that?  No characters were bolded?  These turned out particularly bad, with almost half (10-11) not even being present in Eoraptor.  The others are basically all also found in taxa agreed to be basal theropods (11) and/or sauropodomorphs (7).  The best character is the absent anterior splenial foramen, which depends on illustration inaccuracy of a poorly preserved and seldomly exposed element.

Next up- is it a sauropodomorph?

References- Padian, Hutchinson and Holtz, 1999. Phylogenetic definitions and nomenclature of the major taxonomic categories of the carnivorous dinosaurs Dinosauria (Theropoda). Journal of Vertebrate Paleontology. 19(1), 69-80.

Langer, 2004. Basal Saurischia. In Weishampel, Dodson and Osmolska. The Dinosauria Second Edition. University of California Press. 861 pp.

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.

Yates, 2007. Solving a dinosaurian puzzle: The identity of Aliwalia rex Galton. Historical Biology. 19(1), 93-123.

Martinez and Alcober, 2009. A basal sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the early evolution of Sauropodomorpha. PLoS ONE. 4(2), e4397.

Bittencourt Rodrigues, 2010. Revisao filogenetica dos dinossauriformes basais: Implicacoes para a origem dod dinossauros. Unpublished Doctoral Thesis. Universidade de Sao Paulo. 288 pp.

Martinez, Sereno, Alcober, Columbi, Renne, Montanez and Currie, 2011. A basal dinosaur from the dawn of the dinosaur era in Southwestern Pangaea. Science. 331, 206-210.

Sereno, Martinez and Alcober, 2013. Osteology of Eoraptor lunensis (Dinosauria, Sauropodomorpha). Journal of Vertebrate Paleontology. 32(Supplement to 6), 83-179.