Field of Science

More on Postosuchus kirkpatricki

Postosuchus kirkpatricki was named by Chatterjee (1985) for rauisuchian material from the Post Quarry in the Upper Triassic Dockum Group of Texas. Based on pelvic morphology Chatterjee assigned Postosuchus to the Poposauria. He also noticed strong convergences between Postosuchus and carnosaurian (at the time, large) dinosaurs and argued that Postosuchus was an ancestral carnosaur despite the presence of a crocodilian ankle. However, this was not the first material of a large rauisuchian collected from the American southwest. Case (1943) described a partial pelvis of what he considered to be an aberrant phytosaur from the Dockum Group, and even earlier Charles Camp had collected over 100 bones of a large rauisuchian from the Placerias Quarry in the Chinle Formation of east-central Arizona. In the early 1980s Robert Long collected more material from Petrified Forest National Park (PEFO) and was actively studying the Arizona material, which he planned on naming “Lythrodynastes rectori” (after the superintendent of PEFO) and later “Lythrodynastes rapax” (“greedy gore-lord”). However, these plans were waylaid by the publication of Postosuchus in 1985 (which is named after the town of Post Texas that was named for the nearby cereal plant). After comparing the Arizona material to the type material of Postosuchus, Long conceded that the material all belonged to the same taxon; however, he also noted that the type material was chimaeric and consisted of three different animals (Murry and Long, 1989). Long and Murry (1995) formally named the shuvosaurid “Chatterjeea elegans” (now Shuvosaurus inexpectatus), and the poposaur Lythrosuchus langstoni from portions of the original Postosuchus holotype material. As a result Postosuchus is no longer considered to be a poposaurid. Most of the Arizona material still remains undescribed and in fact the material reposited at the Museum of Northern Arizona still bears the name “Lythrodynastes rapax”.


About 10 years ago Jonathan Weinbaum started repreparing the type material (especially the skull) of Postosuchus, discovering a nearly complete skull under layers of paint, chicken wire, and plaster. His resulting MS thesis (Weinbaum, 2002) and PhD Dissertation (Weinbaum. 2008) provide the most up-to-date and accurate reconstruction of Postosuchus kirkpatricki. In 2008 Peyer et al. described a partial skeleton of a new species, Postosuchus alisonae, from the Upper Triassic of North Carolina. The reconstruction provided by Jeff Martz is based on these works.


Two side notes regarding the taxonomy of Postosuchus. The pelvis described by Case (1943) was found and donated to the University of Michigan Museum of Paleontology by a Texas rancher named William J. Elliot, who aided Case often in his fieldwork and found and donated several specimens from the area around Spur, Texas. At the very end of his 1943 paper, Case asks that “if, as is possible, more abundant material should show this pelvis to be that of a new genus or species it is suggested that the name of Mr. Wm. J. Elliot be associated with it, in recognition of his interest in the local geology and the help he has given many collectors in the Triassic beds of Texas”. To date, this request has never been granted.


Finally, Chatterjee (1985) named Postosuchus kirkpatricki for Mr. and Mrs. Kirkpatrick, therefore by ICZN conventions the specific name should actually be P. kirkpatrickorum. Since 1985 nobody has provided an emendation and the current volume of the code is ambiguous about whether an emendation should be made (as just recently discussed on the Dinosaur Mailing List).


The next post will discuss the bipedal/quadrupedal controversy...


The photo is the Petrified Forest National Park mount based on Robert Long's concept of "Lythrodynastes rapax". Photo is from here.


REFERENCES


Case, E. C. 1943. A new form of phytosaur pelvis. American Journal of Science 241:201–203.


Chatterjee, S. 1985. Postosuchus, a new thecodontian reptile from the Triassic of Texas and the origin of tyrannosaurs. Philosophical Transactions of the Royal Society of London, Series B 309, 395-460; London.


Long, R. A., and P. A. Murry. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science, Bulletin 4:1–254.


Murry, P. A., and R. A. Long. 1989. Geology and paleontology of the Chinle Formation, Petrified Forest National Park and vicinity, Arizona and a discussion of vertebrate fossils of the southwestern Upper Triassic; pp. 29-64 in Lucas, S. G., and A. P. Hunt (eds.), Dawn of the Dinosaurs in the American Southwest, University of New Mexico Press, Albuquerque.


Peyer, K., Carter, J. G., Sues, H.-D., Novak, S. E., and P. E. Olsen. 2008. A new suchian archosaur from the Upper Triassic of North Carolina. Journal of Vertebrate Paleontology 28:363-381.


Weinbaum, J. C. 2002. Osteology and relationships of Postosuchus kirkpatricki (Archosauria: Crurotarsi). Unpublished MS thesis, Texas Tech University, 78pp.


Weinbaum, J. C. 2008. Review of the Triassic reptiles Poposaurus gracilis and Postosuchus kirkpatricki (Reptilia: Archosauria). Unpublished PhD dissertation, Texas Tech University, 183.


New Triassic Critter Reconstruction II

Here is another new Late Triassic critter reconstraction from the Chinle/Dockum courtesy of Jeff Martz. As with the last one I'll leave the ID up to you with discussion to follow.


Congratulations Randy

At this time I would like to congratulate my good friend and colleague Randy Irmis, who just finished his dissertation (Irmis, 2008) at UC Berkeley and is moving to Utah to start his new job as an assistant professor in the Department of Geology and Geophysics at the University of Utah and curator of the Utah Museum of Natural History. Best of luck Randy!


This picture is from his University of Utah faculty webpage.

REFERENCE

Irmis, R.B. 2008. Perspectives on the origin and early diversification of dinosaurs. PhD dissertation, Department of Integrative Biology, University of California, Berkeley, 421 pp.

Petrified Forest Fieldwork Photos - 2008


All of this nasty ice and freezing weather has me longing for summer and fieldwork again. Here are some photos from work in the park this past summer to warm us up a little. The above photo is a picture of a phytosaur skull excavation from May of this year.

Here is our fossil preparator Matt Brown precariously perched excavating a small metoposaurid skull.


Summer intern Kate Hazlehurst working on some poposaurid material from the Sonsela Member.

Poposaurid pubis in-situ.


Myself and Matt Brown carving (literally) a phytosaur skull out of its sandstone tomb. This complete skull is from the type locality of Pseudopalatus jablonskiae and may belong to the same taxon.



Me again, with intern Joanna Panosky excavating aetosaur (Typothorax) plates.


One of the Typothorax plates.

Just to rub it in a little, all of these sites are within an hour drive/hike of my office. Such is the beauty of the Petrified Forest National Park. Hope these warmed you up a bit (at least those of us in the Northern Hemisphere).

The vertebrate assemblage of the Late Triassic Canjilon Quarry and the importance of apomorphy based assemblage comparisons

Nesbitt, S.J., and M.R. Stocker. 2008. The vertebrate assemblage of the Late Triassic Canjilon Quarry (Northern New Mexico, USA) and the importance of apomorphy based assemblage comparisons. Journal of Vertebrate Paleontology 28:1063-1072.

ABSTRACT—The Upper Triassic Canjilon Quarry in northern New Mexico preserves a vertebrate assemblage typical of the Norian Stage of North America. Although dominated in relative abundance by the phytosaur Pseudopalatus and the aetosaur Typothorax, a more diverse assemblage of smaller forms was previously reported. Additions to the Canjilon
Quarry vertebrate assemblage are critically reviewed and described using an apomorphy-based method for assigning taxa. An apomorphy-based approach for compiling and comparing assemblages allows each taxonomic assignment to be a testable hypothesis. Fragmentary yet diagnostic elements that may not be assignable to a species-level taxon can be assigned to a larger clade and thus provide useful information. Additionally, each taxon listed in the assemblage must be tied to a diagnostic specimen listed with a museum specimen number. Using this method for the Canjilon Quarry, we establish the presence of an assemblage that is more similar to other vertebrate quarries near Ghost Ranch than previously thought. The Canjilon Quarry assemblage is restricted to vertebrates from UCMP locality V2816. Vertebrate material housed at the Museum of Comparative Zoology, Harvard, which was reported from the Canjilon Quarry, was not collected from UCMP V2816 but from a nearby locality.

The Canjilon Quarry from the Petrified Forest Member (Chinle Formation) of New Mexico was mainly worked by Charles Camp and crew (University of California, Berkeley) in 1933 and produced a wealth of fossil vertebrate material, most notably numerous skeletons (including a suite of skulls) of the phytosaur Pseudopalatus. You can get more information on the Canjilon Quarry, including an extremely detailed reconstruction of the 1933 excavation from field notes, here and here. Of course the main point and overall importance of this paper is the discussion on using apomorphy based identifications when creating faunal lists.

New Triassic Critter Reconstructions

Not only is Jeff Martz a really good geologist and paleontologist he also is very skilled as an illustrator (check out his M.S. thesis Martz [2002], his skeletal reconstruction of Desmatosuchus [from Parker, 2008], and this link at Discovery News for other examples of his work). Jeff has recently initiated a new series of Late Triassic animal reconstructions from Petrified Forest National Park and has generously offered to let me share some of them on my site rather than showing them on his site. The park has been sorely lacking up-to-date reconstructions of many of its Triassic animals, as most existing reconstructions date from the 1980s and do not include the majority of new finds. This is the first of the series and I won't tell you what taxon this is. Instead I'll leave to you to guess its identity.
These represent slightly different reconstructions of the same animal. It is challenging to try to provide realistic yet thought provoking reconstructions, especially regarding skin color, texture, and soft tissue. The coloration and patterning of most animals fall into a few broad catagories including camouflage, disruptive patterning, and/or sexual display. The animal featured here is most likely a carnivore and thus was provided with more of a disruptive pattern that would allow the animal a mechanism to distract prey by making the body outline hard to see, and thus distance and speed difficult to judge. The upper reconstruction adds hypothesized soft parts including a 'dewlap' and other features which may or may not have been present, and thus are speculative yet feasible for display.

As long as Jeff is willing, I hope to provide more of these new reconstructions in the future.

REFERENCES

Martz, J.W. 2002. The morphology and ontogeny of Typothorax coccinarum (Archosauria, Stagonolepididae) from the upper triassic of the American Southwest. Unpublished M.S. thesis. Texas Tech University, Lubbock.

Parker, W.G. 2008. Description of new material of the aetosaur Desmatosuchus spurensis (Archosauria: Suchia) from the Chinle Formation of Arizona and a revision of the genus Desmatosuchus. PaleoBios , 28:1-40.

Chinle Silesaurid and the Importance of Field Notes

Adam Yates nailed it. The specimen is the proximal end of the right femur of a silesaurid (PEFO 34347) from the Upper Triassic Blue Mesa Member (Chinle Formation) of Arizona. This specimen is significant because it represents the only known unambiguous silesaurid element from the lower portion of the Chinle Formation and from Arizona. It demonstrates that silesaurids were a portion of the fauna at Petrified Forest National Park.

This specimen was discussed in more detail by Parker et al. (2006) and Nesbitt et al. (2007). It is identical to the proximal ends of the femora of Silesaurus opolensis (Carnian of Poland) and Eucoelophysis baldwini (Norian of New Mexico) and thus cannot be assigned to a specific genus although the age (Norian) and stratigraphic position (Chinle Formation) of the specimen would suggests that it is probably could represent Eucoelophysis rather than Silesaurus. However, until more material is found this cannot be considered. A key characteristic of the proximal end of the femur in Silesaurus, Eucoelophysis, and PEFO 34347 is that the element is triangular in proximal view and has a mediolaterally trending sulcus. Whereas this sulcus is present in other taxa, most notably the pseudosuchian Shuvosaurus, the femur of silesaurids differs in having a subrectangular femoral head in lateral view with a slightly offset head as in dinosaurs.

Now for the promised “interesting” (and frustrating) story regarding this specimen. This specimen was collected sometime in the late 1990s by an unknown individual who was part of a larger research project. It went unrecognized and was included in a large amount of material deemed unworthy of study and potentially to be disposed of. When going through this material to see if anything was salvageable I came across this specimen. Unfortunately, the exact spot where the specimen was collected was not recorded. There are no known field notes for the project and field tags contain minimal information, in this case just a vague geographical reference. This reference is enough to pinpoint the specimen to a small geographical area and limited stratigraphic level; however, it will be nearly impossible to find the rest of the specimen if it exists (and the break is clean, suggesting that more of the specimen was preserved and awaits discovery).

I cannot emphasize enough (and I stress this to, and require it from, all of my employees and interns) the importance of collecting and recording accurate field data on every specimen collected whether the specimen seems important or not. I don’t know how I would function without my past field notes when it comes to identifying and interpreting specific specimens. I have found when I get lax (because of time, weather, arrogance, etc..) I usually end of regretting not having a key piece of information regarding a specimen at some point. At the absolute minimum for EVERY specimen collected there should be GPS coordinates, a photograph of the site showing the surrounding landscape (most important), and a brief description of the sediments and stratigraphic position. Taphonomic notes are also extremely important and often forgotten. Bottom line, you cannot collect too much information. Anyone who has worked with older specimens when simply a stratigraphic unit and state were deemed sufficient information will understand. PEFO 34347 currently represents to earliest known silesaurid from North America, yet its provenance cannot be precisely determined and clarification regarding this specimen depends exclusively on luck. Was more of the specimen preserved? Is it still present and will we be able to stumble across it? I certainly hope so.

REFERENCES


Nesbitt, S.J., Irmis, R.B., and W.G. Parker. 2007. A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5:209-243.


Parker, W.G., Irmis, R.B., and S.J. Nesbitt. 2006. Review of the Late Triassic dinosaur record from Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 62:160-161.

Late Triassic Mystery Fossil #4

This is an interesting specimen with an interesting history.....and proof that, to be cliche, one person's junk is another person's treasure (especially if they don't know what they are looking at). Unfortunately that is only half the story, the rest is highly frustrating. Views are lateral and proximal. Scale bar is 1 cm.

First record of stereospondyls from the Upper Triassic of Brazil

Dias-da-Silva, S., Dias, E.V., and C.L. Schultz. 2009. First record of stereospondyls (Tetrapoda, Temnospondyli) in the Upper Triassic of Southern Brazil. Gondwana Research 15:131-136. doi:10.1016/j.gr.2008.07.002

Abstract - Stereospondyls survived the Permo-Triassic extinctions in a refuge probably located in the landmass that nowadays comprises Australia. Subsequently, they radiated to other parts of Pangaea, reaching their highest distribution and diversification during the Early Triassic. An incomplete interclavicle from the Caturrita Formation represents their first record in the Upper Triassic of Brazil. Previously, Upper Triassic South American stereospondyls were restricted to Argentina. This new record reinforces a former hypothesis that suggests the presence of a more diverse stereospondyl fauna in South America during the Late Triassic than previously assumed. Additionally, the presence of a stereospondyl and a phytosaur in the Caturrita Formation reinforces the hypothesis of a change to more humid climatic conditions in the Paraná Basin during the Upper Triassic. The record of Early Triassic stereospondyls in South America suggests that they first colonized Brazil and/or Uruguay, spreading from South Africa during the Early Triassic, subsequently reaching Argentina. Up till now, there is no record of Middle Triassic stereospondyls in either Argentina and Brazil, probably due to either taphonomic bias or insufficient prospecting. Despite the lack of direct evidence, one should not dismiss an earlier stereospondyl colonization of Argentina still during the Early or Middle Triassic.

Feather-like development of Triassic diapsid skin appendages

Thanks to Rob Taylor of the Theropod Archives who just posted on the Dinosaur Mailing List that Naturwissenschaften is freely available online through the end of the month. One of several Online First Titles that is of interest is this one...

Voight, S., Buchwitz, M., Fischer, J., Krause, D., and R. Georgi. Online First 2008. Feather-like development of Triassic diapsid skin appendages. Naturwissenschaften
DOI 10.1007/s00114-008-0453-1

Abstract - Of the recent sauropsid skin appendage types, only feathers develop from a cylindrical epidermal invagination, the follicle, and show hierarchical branching. Fossilized integuments of Mesozoic diapsids have been interpreted as follicular and potential feather homologues, an idea particularly controversially discussed for the elongate dorsal skin projections of the small diapsid Longisquama insignis from the Triassic of Kyrgyzstan. Based on new finds and their comparison with the type material, we show that Longisquama’s appendages consist of a single-branched internal frame enclosed by a flexible outer membrane. Not supporting a categorization either as feathers or as scales, our analysis demonstrates that the Longisquama appendages formed in a two-stage, feather-like developmental process, representing an unusual early example for the evolutionary plasticity of sauropsid integument.

The PDF and online supplemental material is also available from the same site.

Looking at Aetosaurs in a Whole New Way

Jeff Martz's recent post at Paleo Errata reminded me of this recent article which came out two months ago. Check it out, you can tell that the writer had a lot of fun with this, and the photo (see courtesy photo from http://www.santafenewmexican.com/ below) is great.


Of course, one comment made in the article regarding the similarity to modern crocodiles led to a Google search which turned up what could best be described as um....., you got it, croc porn.

All of this aside, what a great specimen of Typothorax!

On the Procompsognathus postcranium

ResearchBlogging.org

F KNOLL (2008). On the Procompsognathus postcranium (Late Triassic, Germany)☆ Geobios, 41 (6), 779-786 DOI: 10.1016/j.geobios.2008.02.002

ABSTRACT - A review of the historical background of the material housed in the Staatliches Museum für Naturkunde (Stuttgart) and ascribed to Procompsognathus triassicus (Upper Triassic, Germany) is provided. The systematic position of the postcranial remains is discussed. The combined results of cladistic analyses suggest that the type material, an incomplete postcranial skeleton in two pieces (SMNS 12591), is from a theropod close to Segisaurus and Coelophysis. An isolated manus (SMNS 12352a) is definitely not theropodan, but could be from any small basal archosaur. The remarkable diversity of the carnivorous guild that dwelled in southern Germany before the end-Triassic events is underlined.



This is the latest paper in the Procompsognathus saga, regarding the taxonomic status of four specimens refered to this taxon, a purported theropod dinosaur, from the Late Triassic of Germany. To recap, Fraas (1913) named Procompsognathus triassicus based on a partial skeleton (SMNS 12591a) and skull (SMNS 12591), and refered it to the Dinosauria. Huene (1921) discussed the material further and assigned another partial skull (SMNS 12352) and manus (SMNS 12352a) from the same quarry to the taxon. Since that time this material has been reviewed by Ostrom (1981), Sereno and Wild (1992), Chatterjee (1993, 1998), Rauhut and Hungerbuhler (2000), Rauhut (2003), Allen (2004), and most recently by Knoll and Schoch (2006) which was an abstract previewing the current study by Knoll. All of these authors came to differing conclusions regarding the taxonomic affinities of the material as listed below:

Ostrom (1981)
SMNS 12591 - Procompsognathus triassicus
SMNS 12591a - Procompsognathus triassicus
SMNS 12352 - non Procompsognathus triassicus
SMNS 12352a - non Procompsognathus triassicus

Sereno and Wild (1992)
SMNS 12591 - Theropod similar to Coelophysis and Segisaurus
SMNS 12591a - Saltoposuchus connectens (Crocodylomorpha)
SMNS 12352 - Saltoposuchus connectens
SMNS 12352a - Saltoposuchus connectens

Chatterjee (1993, 1998)
SMNS 12591a - Theropod (contra Sereno and Wild [1992])

Rauhut and Hungerbuhler (2000)
SMNS 12591 - Theropod similar to Coelophysis and Segisaurus

Rauhut (2003)
Procompsognathus is a theropod but a metataxon

Allen (2004)
Procompsognathus is a non-dinosaurian ornithodiran

Knoll and Schoch (2006)
SMNS 12591 - Theropod similar to Coelophysis and Segisaurus
SMNS 12591a - Theropod, possibly tetanuran
SMNS 12352 - indeterminate crocodylomorph
SMNS 12352a - indeterminate crocodylomorph

The current paper (Knoll, 2008) follows the finding of Knoll and Schoch (2006) except that the isolated manus (SMNS 12352a) is considered to represent an unknown basal archosaur. Thus Knoll (2008) argues for a previously unrecognized diversity of carnivorous archosaurs in the Upper Triassic Stubensandstein. Hopefully this is the final word, but given the numerous differing hypotheses put forth this taxonomic argument may never be fully resolved.

The image is from here.

REFERENCES

Allen, D. 2004. The phylogenetic status of Procompsognathus revisited. Journal of Vertebrate Paleontology 24:34A.

Chatterjee, S. 1993. Procompsognathus from the Triassic of Germany is not a crocodylomorph. Journal of Vertebrate Paleontology 13:29A.

Chatterjee, S. 1998. Reassessment of the Procompsognathus skull, p. 6 in Wolberg, D.L., Gittis, K., Miller, S., Carey, L., and A. Raynor (eds.), Dinofest International. The Academy of Natural Sciences, Philadelphia.

Fraas, E. 1913. Die neuesten Dinosaurierfunde in der schwabischen Trias. Die Naturwissenschaften 1:1097-1100.

Huene, F.v. 1921. Neue Pseudosuchier und Coelurosaurier aus dem wurttembergischen Keuper. Acta Zoologica 2:329-403.

Knoll, F., and R. Schoch. 2006. Does Procompsognathus have a head? Systematics of an egnimatic Triassic taxon. Journal of Vertebrate Paleontology 26:86A.

Knoll, F. 2008. On the Procompsognathus postcranium (Late Triassic, Germany). Geobios 41:779-786.

Ostrom, J.H. 1981. Procompsognathus - theropod or thecodont? Palaeontographica A 175:175-195.

Rauhut, O.W.M. 2003. The interrelationships and evolution of basal theropod dinosaurs. Special Papers in Palaeontology 69:1-213.

Rauhut, O.W.M., and A. Hungerbeuhler. 2000. A review of European Triassic theropods. GAIA 15:75-88.

Sereno, P.C., and R. Wild. 1992. Procompsognathus: theropod, "thecodont", or both? Journal of Vertebrate Paleontology 12:435-458.

Proofing The Proof Corrections?

OK...this has happened to me more than once so I would like to comment and hopefully receive some feedback. You send in your final revisions for your manuscript and it is accepted by a journal. Sometime later you receive the proofs with the layout for final publication and a request for you to check it over and correct any final typos and/or problems with the layout. You submit your proposed changes within the time alloted and sometime later the manuscript is finally published. Upon reading through the published manuscript you see where some but not all of the changes you requested in the proofs were made, and thus there may still be some annoying errors (typos and/or layout) that you thought were going to be fixed. I am not talking about major changes being requested (which are costly at the proof stage and thus may not be approved by the editors). Instead this is about small corrections that for some reason were not made.

What do you do next? Of course you can contact the editors and point out were requested corrections were not made, but what does this approach get you? An apology and possibly an erratum in the next issue, but does not fix the actual publication (which is now a permanent record). Maybe it is possible to actually proof the proof corrections? I'm not aware of any journal that does this, but I may start asking.

I guess that hypothetically through the writing, review, and rewriting stages all mistakes should have been eliminated, however, anyone who publishes knows that this is not the case. In fact, the proof stage is one of the most important parts of the whole process because it represents the first time the manuscript has been out of the author's control and as I said earlier it represents the permanent record of your work. Wouldn't you like just one last look before it finally does print? I actually had one manuscript a few years back where we did not even get proofs! The final result was not good and we actually felt obliged to add a disclaimer to the reprints and PDFs that we distributed.

Has anyone else had a problem with this? How common is this type of error?