Halticosaurus orbitoangulatus is a Pseudosuchian, Not a Dinosaur

Brian Switek has the details regarding this new study at his blog Laelaps.

Sues, H.-D., and R. R. Schoch. 2013. Reassessment of cf. Halticosaurus orbitoangulatus from the Upper Triassic (Norian) of Germany – a pseudosuchian, not a dinosaur. Zoological Journal of the Linnean Society 168(4): 859–872 DOI: 10.1111/zoj.12038

Abstract - The holotype of cf. Halticosaurus orbitoangulatus Huene, 1932, comprises an incomplete and macerated but associated skull of an archosaurian reptile from the middle (second) Stubensandstein (middle Löwenstein Formation; Upper Triassic: Norian) of Baden-Württemberg, Germany. It was originally interpreted as a theropod dinosaur but more recently it has been suggested that this taxon has crocodylomorph affinities. Detailed preparation of the holotype of cf. H. orbitoangulatus has revealed much new anatomical information and permitted reassessment of its affinities. The maxilla lacks both a distinct antorbital fossa and a medial bony lamina bordering the antorbital fenestra. The lateral surface of the dentary bears a pronounced horizontal ridge. The squamosal differs from that of basal crocodylomorphs in being L-shaped rather than arcuate in dorsal view, lacking a dorsolateral overhang, and lacking an interlocking contact with the paroccipital process as, for example, in the basal crocodylomorph Saltoposuchus connectens from the same horizon and locality. Phylogenetic analysis placed cf. H. orbitoangulatus amongst loricatan pseudosuchians (but not amongst Crocodylomorpha) rather than amongst theropod dinosaurs. The holotype of cf. H. orbitoangulatus represents a previously unrecognized taxon of loricatan pseudosuchian, which is here named Apatosuchus orbitoangulatus and set apart from other known Norian-age non-crocodylomorph loricatans by its apparently much smaller size.

Albinykus baatar, a New Small Alverezsaurid From the Late Cretaceous of Mongolia

I know it's not Triassic, but I have to give props to my friends, colleague, and two of my grad school advisors!

Nesbitt, S. J., Clarke, J. A., Turner, A. H., and M. A. Norell. 2011. A small alvarezsaurid from the eastern Gobi Desert offers insight into evolutionary patterns in the Alvarezsauroidea. Journal of Vertebrate Paleontology 31:144-153. DOI: 10.1080/02724634.2011.540053

Abstract - A partial postcranial skeleton of a small alvarezsaurid from the Late Cretaceous of the Mongolian eastern Gobi Desert locality of Khugenetslavkant represents the first reported articulated theropod material from that locality. The specimen is recognized as the holotype of a new taxon herein named Albinykus baatar, gen. et sp. nov. Phylogenetic analysis places Albinykus within Alvarezsauridae as the sister taxon of Shuvuuia, another Late Cretaceous Mongolian taxon from the slightly younger Djadokhta Formation. The complete coossification of the proximal tarsals with the tibia, and of the distal tarsals and proximal metatarsals, present in Albinykus are previously unknown in Alvarezsauridae. Extensive fusion is consistent with histological data from the tibia indicating that the individual was a subadult. These results are striking given that Albinykus is among the smallest known non-avian dinosaurs with a body mass no greater than 1 kg and ranks among the smallest known alvarezsaurids. Alvarezsauridae shows a decreasing size trend throughout its evolutionary history, a rarity among dinosaurian clades. Within maniraptoran dinosaurs, such a trend has thus far only been recognized within Avialae and at the origin of Paraves with respect to other coelurosaurs. The holotype was recovered articulated in a 'seated' position, with hind limbs aligned and the feet tucked under the body. This body posture, which is present in Aves, has been previously noted in other maniraptoran clades (i.e., Oviraptoridae Troodontidae) and is now recognized in Alvarezsauridae.

A New Late Triassic Theropod, Tawa hallae, and its Implications for Early Dinosaur Evolution

A new Late Triassic basal theropod, Tawa hallae, is described by Nesbitt et al. (2009) in a new paper out today in Science. Tawa is known from two relatively complete skeletons and other isolated material from the Hayden Quarry at Ghost Ranch New Mexico [another link]. The Hayden Quarry is in the Petrified Forest Member of the Chinle Formation.

This quarry is an absolutely spectacular site that is proving to be the most diverse locality in the Chinle Formation, even more than the famed Coelophysis Quarry (which is close geographically but higher stratigraphically). Other taxa found at this site include Dromomeron romeri, Chindesaurus bryansmalli, Eucoelophysis baldwini, a coelophysoid theropod, and a shuvosaurid as well as various aetosaurs, crocodylomorphs, rauisuchians, phytosaurs, drepanosaurs, metoposaurs, and fish (Irmis et al. 2007).

Key points of the paper:

• Tawa possesses a mix of “coelophysoid” (Neotheropoda) and herrerasaurid characters that help clarify basal saurischian relationships.

- Herrerasaurids (Herrerasaurus, Chindesaurus, Staurikosaurus) and Eoraptor are unambiguously nested within Theropoda.

- Tawa is the sister taxon to Neotheropoda (see phylogenetic reconstruction artwork and tree below).

- Coelophysoidea is found to be paraphyletic, with the hypothesis that this clade had been serving as a “phylogenetic vacuum cleaner”, picking up deep theropod synapomorphies and ceratosaur/tetanuran reversals and treating them as coelophysoid synapomorphies.

• The presence of cervical pleurocoels in Tawa supports the hypothesis that cervical air sacs predate the origin of Neotheropoda and may be ancestral for Saurischia.

• The age of the Hayden Quarry (~215-213) and comparison with the Ischigualasto fauna supports the hypothesis of the diachronous evolution of Triassic dinosaur faunas.

• The presence of Dromomeron, Chindesaurus, Tawa, and a basal neotheropod in the Hayden Quarry suggests that the North American theropod fauna was not endemic, an was the result of several dispersals of taxa from South America.

• This prevalence of dispersal among early dinosaurs and other Triassic reptile groups indicates that physical barriers did not prevent these groups from moving around Pangaea - specifically into North America. Thus the question is why didn't sauropodomorphs and ornithischians make it to North America during the Triassic? Nesbitt et al. hypothesize that they were excluded by climate.

Dentary of Tawa hallae


Reconstruction of the head of Tawa hallae.


Articulated manus of Tawa hallae


In-situ articulated limbs of Tawa hallae


Associated dentary and maxilla of Tawa hallae



Block containing skull and other bones.

Thanks to Randy Irmis and Sterling Nesbitt for providing the photos and reconstructions used here. The reconstructions are by Jorge Gonzalez.

Links to some early news articles [here] [here] [here]

Link to National Science Foundation special report with lots of additional information on Tawa, its discovery, and its finders.

REFERENCES

Irmis, R. B, Nesbitt, S. J., Padian, K., Smith, N. D., Turner, A. H, Woody, D., and A. Downs. 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317:358–361.

Nesbitt, S. J., Smith, N. D., Irmis, R. B., Turner, A. H., Downs, A., and M. A. Norell. 2009. A complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs. Science 326:1530-1533.

Cruxicheiros newmanorum, a new Middle Jurassic Theropod from England

Benson, R. B. J., and J. D. Radley. in press. A new large-bodied theropod dinosaur from the Middle Jurassic of Warwickshire, United Kingdom. Acta Palaeontologica Polonica, available online 20 Nov 2009.

Abstract - Previously undocumented postcranial material from the Chipping Norton Limestone Formation (Middle Jurassic: Lower Bathonian) of Cross Hands Quarry, near Little Compton, Warwickshire represents a new large-bodied theropod dinosaur, distinct from the contemporaneous Megalosaurus bucklandii. Cruxicheiros newmanorum gen. et sp. nov. is diagnosed by a single autapomorphy, the presence of a proximomedially inclined ridge within the groove that marks the lateral extent of the posterior flange of the femoral caput (trochanteric fossa). C. newmanorum shows three tetanuran features: widely separated cervical zygapophyses, a swollen ridge on the lateral surface of the iliac blade and an anterior spur of the caudal neural spines. However, due to fragmentary preservation its affinities within Tetanurae remain uncertain: phylogenetic analysis places it as the most basal tetanuran, the most basal megalosauroid (= spinosauroid) or the most basal neotetanuran.

Tyrannosauroid from the Bathonian (Middle Jurassic) of England

Important new Jurassic paper for those of you not subscribed to the VRTPALEO listserve...

RAUHUT, O.W.M., A.C. MILNER, and S. MOORE-FAY. 2009. Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi(Woodward, 1910) from the Middle Jurassic of England. Zoological Journal of the Linnean Society Early View doi: 10.1111/j.1096-3642.2009.00591.x

ABSTRACT
The cranial osteology of the small theropod dinosaur Proceratosaurus from the Bathonian of Minchinhampton, England, is described in detail, based on new preparation and computed tomography (CT) scan images of the type, and only known, specimen. Proceratosaurus is an unusual theropod with markedly enlarged external nares and a cranial crest starting at the premaxillary-nasal junction. The skull is highly pneumatic, with pneumatized nasals, jugals, and maxillae, as well as a highly pneumatic braincase, featuring basisphenoid, anterior tympanic, basipterygoid, and carotid recesses. The dentition is unusual, with small premaxillary teeth and much larger lateral teeth, with a pronounced size difference of the serrations between the mesial and distal carina. The first dentary tooth is somewhat procumbent and flexed anteriorly. Phylogenetic analysis places Proceratosaurus in the Tyrannosauroidea, in a monophyletic clade Proceratosauridae, together with the Oxfordian Chinese taxon Guanlong. The Bathonian age of Proceratosaurus extends the origin of all clades of basal coelurosaurs back into the Middle Jurassic, and provides evidence for an early, Laurasia-wide, dispersal of the Tyrannosauroidea during the late Middle to Late Jurassic.

Limusaurus and Bird Digit Identity

For those of you who may have missed this or are not subscribed to the Dinosaur Mailing List, this is a comment left for my recent post on Limusaurus, the strange new beaked ceratosaur from China. One of the purported significances of this specimen is that it shed light on the debate on dinosaur digit homologies. As you can see below, this new article is a response to that claim.

A. Vargas has left a new comment on your post "Limusaurus inextricabilis, a Bizarre Beaked Cerato...":

Vargas, AO, Wagner GP, and Gauthier, JA. Limusaurus and bird digit identity.

hdl.handle.net/10101/npre.2009.3828.1

Here is our response to the Limusaurus paper. It was recently rejected by nature, not for any technical reason but because it was considered not to be of sufficient interest/importance.
We have uploaded it at the nature precedings citable archive, because we think it is important there is a quick and citable reply that unlike Xu’s proposal, is consistent with the view of the larger community of theropod paleontologists, namely, that tetanuran digits still are I, II, III. We are preparing a longer paper on this topic.

Cute! Raptorex kriegsteini New Miniature Tyrannosaur from the Early Cretaceous of China

This isn't Triassic, but it has been a slow month and this is pretty cool. Out today in Science is an article describing a new miniature tyrannosaur from the Early Cretaceous of China. Sereno et al. have named the specimen Raptorex kriegsteini after the parents of the benefactor who purchased the specimen from a private seller at the Tucson Gem and Mineral Show. This is a good story about how an illegally collected specimen is donated by a benefactor to science, studied and published for the scientific community and the public, and now will be returned back to China from where it was removed.

You can read more on this find here:

http://www.chicagotribune.com/news/chi-090917little-t-rex,0,2156860.story

http://www.sciencenews.org/view/generic/id/47453/description/Tiny_T.rex%E2%258

http://scienceblogs.com/notrocketscience/2009/09/raptorex_tiny_king_of_thieves_shows_how_tyrannosaurus_body_p.php

The reconstruction is from here. Todd Marshall does amazing work.

One thing I did notice is that the species name is improperly constructed. Because the specimen is named for Mr. and Mrs. Kriegstein, by ICZN convention the name should be R. kriegsteinorum. This seems to occur more often then it should, especially with multiple authors, reviewers, and editors.

REFERENCE

Sereno, P.C., Tan, L., Brusatte, S., Kriegstein, H.J., Zhao, X., and K. Cloward. 2009. Tyrannosaurid body design first evolved at small body size. Science 325. doi: 10.1126/science.1177428

Supplemental Material

Citation and Abstract for Nothronychus graffami

Part II of my earlier post. Here is the abstract of the new paper.

Zanno, L.E, Gillette, D.D., Albright, L.B., and A.L. Titus. 2009. A new North American therizinosaurid and the role of herbivory in ‘predatory’ dinosaur evolution.Proceedings of the Royal Society B. Published online before print July 15, 2009, doi: 10.1098/rspb.2009.1029

Historically, ecomorphological inferences regarding theropod (i.e. ‘predatory’) dinosaurs were guided by an assumption that they were singularly hypercarnivorous. A recent plethora of maniraptoran discoveries has produced evidence challenging this notion. Here, we report on a new species of maniraptoran theropod, Nothronychus graffami sp. nov. Relative completeness of this specimen permits a phylogenetic reassessment of Therizinosauria—the theropod clade exhibiting the most substantial anatomical evidence of herbivory. In the most comprehensive phylogenetic study of the clade conducted to date, we recover Therizinosauria as the basalmost maniraptoran lineage. Using concentrated changes tests, we present evidence for correlated character evolution among herbivorous and hypercarnivorous taxa and propose ecomorphological indicators for future interpretations of diet among maniraptoran clades. Maximum parsimony optimizations of character evolution within our study indicate an ancestral origin for dietary plasticity and facultative herbivory (omnivory) within the clade. These findings suggest that hypercarnivory in paravian dinosaurs is a secondarily derived dietary specialization and provide a potential mechanism for the invasion of novel morpho- and ecospace early in coelurosaurian evolution—the loss of obligate carnivory and origin of dietary opportunism.

New North American Therizinosaur Nothronychus graffami

Alright...now I'm up into the Cretaceous rather than the Triassic or even the Jurassic. However, it is good to see this beastie finally published after a lot of hard work and many trials and tribulations. Today (July 15) a paper (I don't have the actual ref yet) comes out in Procedings of the Royal Society B by David Gillette and Lindsay Zanno describing a new therizinosaur from the Tropic Shale of Utah. I was a graduate student at Northern Arizona University when Merle Graffam discovered the holotype specimen. Dave Gillette, one of my graduate advisors, collected the specimen in 1999 and laboriously prepared the specimen in the lab where I was working on the skeleton of Desmatosuchus that was the focus of my Masters thesis.

The therizinosaur skeleton was difficult to prepare due to the matrix and diagenetic crushing of the elements, but at the time it was collected it represented the first evidence of therizinosaurs from North America. Doug Wolfe and colleagues had not yet figured out that part of the frill of Zuniceratops was actually the ischium of what would later be named Nothronychus mckinleyi; and the Crystal Geyser Quarry, which would produce Falcarius, had not yet yielded any recognized therizinosaur material. What made the MNA fossil even more spectacular was its stratigraphic control. It was found in a marine deposit and the bones were actually covered with ammonites!

Shortly afterwards the MNA had some problems and at one point the Geology program was terminated. Fortunately due to public outcry (among other things) the department was reestablished; however, these circumstances caused delays in the study of this specimen. A couple of years ago; however, it was the focus of an excellent new exhibit at the MNA and now the description is finally out. As I have not yet seen the paper I cannot comment on the content but there are some early news reports up here and here. Congrats to Dave Gillette (and to Lindsay Zanno) on the release of the results of this long awaited study. I know that he put a ton of work into this specimen.



You can read an earlier account of this excavation and specimen that came out in Arizona Geology back in the summer of 2007. There is also a good photo gallery of Utah fossils here which includes a reconstruction of N. graffami by artist Victor Leshyk (see photo above), pictures of a display of some of the bones, as well as a picture of Dave in front of a full scale reconstruction done by Rob Gaston.

Limusaurus inextricabilis, a Bizarre Beaked Ceratosaur from the Late Jurassic of China

OK...OK....This post is regarding the Jurassic, and the Late Jurassic specifically, but it is almost Triassic right? Sort of? Still, this is just to cool of a discovery not to mention.

Today's issue of Nature contains an article by Dr. James Clark (George Washington University) and Xu Xing (Chinese Academy of Science's Institute of Vertebrate Paleontology and Paleoanthropology in Beijing) and colleagues titled "A Jurassic ceratosaur from China and its significance fortheropod digit reduction and avian digital homologies". The paper describes a new beaked ceratosaur (yes, beaked ceratosaur) from the Jurassic of China. This new specimen also offers key information regarding the interpretation of digit homology between non- avian and avian dinosaurs.

As Tom Holtz noted to me in an earlier e-mail message....this is a "ceratosaur convergent on Effigia (a Triassic pseudosuchian): Truly weird!". I could not have summed it up any better!

Kudos also to my friend and colleague Sterling Nesbitt and to fellow blogger David Hone who are co-authors on this paper.

The following text is from the Reuters News Release . Photos are from here.

Limusaurus inextricabilis (meaning "mire lizard who could not escape") was found in 159 million-year-old deposits located in the Junggar Basin of Xinjiang, northwestern China. The dinosaur earned its name from the way its skeletons were preserved, stacked on top of each other in fossilized mire pits that were the subject of a 2008 National Geographic film, "Dino Death Trap."

A close examination of the fossil shows that its upper and lower jaws were toothless, demonstrating that the dinosaur possessed a fully developed beak. Its lack of teeth, short arms without sharp claws and possession of gizzard stones suggest that it was a plant-eater, though it is related to carnivorous dinosaurs.

The newly discovered dinosaur's hand is unusual and provides surprising new insights into a long-standing controversy over which fingers are present in living birds, which are theropod dinosaur descendants. The hands of theropod dinosaurs suggest that the outer two fingers were lost during the course of evolution and the inner three remained. Conversely, embryos of living birds suggest that birds have lost one finger from the outside and one from the inside of the hand.

Unlike all other theropods, the hand of Limusaurus strongly reduced the first finger and increased the size of the second. Drs. Clark and Xu and their co-authors argue that Limusaurus' hand represents a transitional condition in which the inner finger was lost and the other fingers took on the shape of the fingers next to them. The three fingers of most advanced theropods are the second, third and fourth fingers -- the same ones indicated by bird embryos -- contrary to the traditional interpretation that they were the first, second and third.

Limusaurus is the first ceratosaur known from East Asia and one of the most primitive members of the group. Ceratosaurs are a diverse group of theropods that often bear crests or horns on their heads, and many have unusual, knobbyfingers lacking sharp claws.The fossil beds in China that produced Limusaurus have previously yielded skeletons of a variety of dinosaurs and contemporary animals described by Drs.Clark and Xu and their colleagues. These include the oldest tyrannosaur, Guanlong wucaii; the oldest horned dinosaur, Yinlong downsi; a new stegosaur, Jiangjunosaurus junggarensis; and the running crocodile relative, Junggarsuchus sloani.

REFERENCE

Xing Xu et al, 2009. A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature 459:940. doi:10.1038/nature08124

New Early Middle Jurassic Tetanuran Theropod from China

Well this appears to be Jurassic week on Chinleana. Again not a Triassic specimen, but early Middle Jurassic dinosaurs tend to be rare and this one appears to be a fairly plesiomorphic tetanuran. The authors claim that it is more plesiomorphic than Sinraptor, Yangchuanosaurus, and "Szechuanosaurus", although they were not able to support this with a phylogenetic analysis at this time.

Wu, X., Currie, P.J., Dong, X., Pan, S., and T. Wang. 2009. A new theropod dinosaur from the Middle Jurassic of Lufeng, Yunnan, China. Acta Geologica Sinica 83:9-24.

Abstract – A new theropod dinosaur, Shidaisaurus jinae gen. et sp. nov., has been described on the basis of an incomplete skeleton. The specimen was found near the base of the Upper Lufeng Formation (early Middle Jurassic) in Yunnan, China. It is the first theropod dinosaur from the Middle Jurassic of Yunnan. Shidaisaurus jinae is distinguishable from other Jurassic theropods by certain features from the braincase, axis, and pelvic girdle. The absence of any pleurocoels in the axis or in any anterior dorsal vertebrae suggests that the new Lufeng theropod is relatively primitive and more plesiomorphic than most of the Middle to Late Jurassic theropods from China. Most Chinese taxa of Jurassic theropod dinosaurs have not been well described; a further detailed study will be necessary for us to determine their phylogenetic relationships with Shidaisaurus jinae.

Everything You Ever Wanted to Know About Theropod Furculae

Here is an important new paper by my friends and colleagues Sterling Nesbitt and Alan Turner. Where was this paper months back when we had a detailed discussion/disagreement on dinosaur furcula homology in my Age of the Dinosaurs class?

Nesbitt, S.J., Turner, A.H., Spaulding, M., Conrad, J.L., and M. A. Norell. 2009. The theropod furcula. Journal of Morphology early view. DOI: 10.1002/jmor.10724

ABSTRACT - The furcula is a structure formed by the midline fusion of the clavicles. This is the element which is unique to theropods and is important for understanding the link between birds and other theropods. New specimens from basal theropods suggest that the furcula appeared very early in theropod history. We review furcula development, function, and morphology, as well as the anatomical terminology applied to it. Furcular morphology is highly variable in crown-group avians but is rather conserved among nonavian theropods. Here we review, or describe for the first time, the furculae in many nonavian theropods. Furculae occur in nearly all major clades of theropods, as shown by new theropod specimens from the Early Cretaceous of China and a close inspection of previously collected specimens. Informative phylogenetic characters pertaining to the furcula occur throughout Theropoda, though care should be take to consider taphonomic effects when describing furcular morphology.

Polish Dragon

Despite needing to prepare for my first class lecture for my upcoming Age of Dinosaurs class which meets in less than a week, setting up for my kids (twins) 4th birthday party, and being behind on at least 12 manuscripts, reviews, etc.... I for some bizarre reason have decided to try my hand at blogging. Over the last year and a half I have for various reasons regularly monitored several blogs including SV-POW, Tetrapod Zoology, Dracovenator, and Dinochick Blogs and feel compelled to tackle such a chore myself in order to expend some, hopefully, creative energy. Obviously, given my background and employer my posts may deal heavily in Late Triassic paleontology; however, I hope to include posts on other subjects as I feel inclined. I realize that once I get started I will need to post somewhat regularly and hope to provide at least one post a week. I am also toying with the idea of having "guest" bloggers occasionally fill in when my creative energy is nil. Thus I hope that readers will check back from time to time and hopefully enjoy some of my offerings. The first is below.

This story has been bouncing around for about three weeks right now, the discovery of some significant fossil vertebrates from the Late Triassic in Poland. Dr. Jerzy Dzik and colleagues have announced the find of a large theropod and dicynodont from a quarry in Lisowice in southern Poland. What is very interesting about these finds are 1) the proposed age of the deposit, and 2) the proposed taxonomic affinities of the theropod. The deposit is believed to date around 205 +/-5 ma which would make it very late Norian or Rhaetian in age. This is significant given the discovery of the dicynodont, which are not only very rare in Laurasia, but believed (with the exception of a purported Cretaceous occurrence in Australia) to have fallen victim to an extinction event before the end of the Triassic. This find extends the range of Triassic dicynodonts more than 10 million years. As a Triassic worker I find this interesting because recent work by myself and colleagues Randall Irmis, Sterling Nesbitt, and Jeff Martz have found that the Late Triassic faunas of the Chinle Formation and Dockum Group of the southwestern United States remain relatively conservative throughout the Norian and presumably the Rhaetian. Thus, the fauna from the Placerias Quarry, low down in the Chinle, is pretty similar to the fauna from Ghost Ranch which is much higher in the section. An exception to this appeared to be the dicynodonts, which had never been found in the upper Chinle or Dockum. Because of the Lisowice find, it appears that dicynodonts were present throughout the Late Triassic as well.

The theropod is of interest because of its large size (5m in length and 1.5 meters tall according to Dzik and colleagues) and because the preserved material, including an almost complete skull, suggest tetanuran affinities which would make it the earliest known member of that clade. This distinction was previously held by Zupaysaurus from the Late Triassic of Argentina, which in more recent studies is now believed to be a coelophysoid. A recent study by Nesbitt et al. (2007) has suggested that at least in North America theropod dinosaurs were not only rare components of Late Triassic faunas but only consisted of coelophysoids. Although this has not yet been confirmed by a rigorous study for the rest of Pangaea it appears that this may be true for the rest of the world as well, thus the new Polish find would be of some significance.

To date only a couple of preliminary articles, with some great photos of the material (here and here), have been put forth on what is being called the "Dragon of Lisowice" and hopefully the peer reviewed publications will be out soon.


REFERENCE

Nesbitt, Sterling J., Randall B. Irmis, and William G. Parker. 2007. A critical reevaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5(2):209-243.