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.


4 comments:

  1. Does Jonathan have any of his thesis/dissertation published yet? I am curious to see it if you can direct me towards it.

    ReplyDelete
  2. Hi Rebecca,

    Jonathan has already published a portion of his dissertation, the part on Poposaurus. The Postosuchus description should be next. You can also see the new skull reconstruction on exhibit at the Museum at Texas Tech.

    Bill

    REFERENCE

    Weinbaum, J. C., and A. Hungerbühler. 2007. A revision of Poposaurus gracilis (Archosauria: Suchia) based on two new specimens from the Late Triassic of the southwestern U.S.A. Palaeontologische Zeitschrift 81(2):131-145.

    ReplyDelete
  3. Jonathan is trying to get the skull description paper finished even as we speak; he just finished his first semester at Southern Connecticut State, which slowed him down. There is also supposedly a paper in the works by Jonathan, Sterling Nesbitt and Alan Turner describing a very interesting and phylogenetically relevant aspect of the skull...
    The new skull reconstruction by Jonathan is pretty cool. He just cleaned up all the individual elements of the holoype skull, which are beuatifully preserved, cast them, and assembled them. They fit together perfectly, and the drawing he did of it came out really well. The new reconstruction is even more big theropod-looking then Chatterjee's 1985 reconstruction, and it isn't hard to see why Chatterjee thought it was related to tyrannosaurs.

    LNJ

    ReplyDelete
  4. Cool! I remember Jonathan cleaning all the elements up and all the weird stuff that was on there. I look forward to seeing his work up of it :)

    ReplyDelete

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