Tuesday, January 18, 2011

Pseudopalatus

Pseudopalatus. Image modified from original by Jeff Martz.

Meaning: "false palate"
Species: P. pristinus Mehl, 1928; P. buceros Cope, 1881; P. mccauleyi Ballew, 1989; and P. jablonski Parker and Irmis, 2006
Nominal Author: Mehl, 1928
Age: Late Triassic
Location: Southwestern USA
Physical Characteristics: A large (3-4 meter) phytosaur with a robust rostrum and distinct dorsal crest.


Phylogenetic Position and Species Status
Currently, there are four species of Pseudopalatus, with P. pristinus and P. buceros being the most closely related and most derived and P. jablonskiae being the most basal (Parker and Irmis, 2006). It has been suggested multiple times that P. pristinus and P. buceros are sexual dimorphs of a single species (Camp, 1930; Colbert, 1947; Lawler, 1979; Zeigler et al, 2002; Zeigler et al, 2003), but the evidence is still inconclusive. The validity of P. mccauleyi as a species has also been contested (Long and Murry, 1995; Zeigler et al, 2002; Zeigler et al, 2003), but recent phylogenetic analyses have supported its position, especially when the newest species, P. jablonskiae, is considered (Ballew, 1989; Hungerbuhler, 2002; Parker and Irmis, 2006). The genus Pseudopalatus has been found to be most closely related to Redondasaurus, followed by Mystriosuchus, and when these three are combined with Nicosaurus, they constitute Pseudopalatinae (Hungerbuhler, 2002; Parker and Irmis, 2006).

Phylogeny of Pseudopalatinae from Hungerbuhler, 2002 (47 characters; tree length: 113; CI: 0.73; RI: 0.54; bootstrap values shown). A similar MPT was recovered by Parker and Irmis, 2006, with the addition of the newer species, P. jablonskiae (which was found to be the most basal member of Pseudopalatus).

A Revised Diagnosis of Pseudopalatus
With the addition of P. jablonskiae, Parker and Irmis revised the diagnosis of the genus in 2006. They included four of Hungerbuhler's characters, which include a strongly developed medial lamella of the postorbito-squamosal bar with the supratemporal fenestra reduced to a slit (character 19), a rounded top of the parieto-supraoccipital complex (character 24), the lamina of the squamosal extends onto the paroccipital process forming the ventrolateral border of the posttemporal fenestra (character 38), and a posttemporal fenestra less than three times wider than high (character 41) (2002). Pseudopalatus also differs from all other phytosaurs in that the dorsal position of the squamosals are mediolaterally expanded forming a shelf level with the parietal and postorbital (Parker and Irmis, 2006). Finally, Pseudopalatus differs from Redondasaurus in having a supratemporal fenestra that is visible in dorsal view.

Biostratigraphy
Pseudopalatus is a stratigraphically significant taxon. Lucas and Hunt (1993) designated Pseudopalatus as an index taxon for the Revueltian (early-middle Norian), with the first appearance datum for Pseudopalatus representing the end of the Adamanian land vertebrate faunachron and the beginning of the Revueltian land vertebrate faunachron. The addition of P. jablonkiae is significant in that it is the stratigraphically lowest occurrence of Pseudopalatus, suggesting an overlap of the Adamanian and Revueltian LVFs (Parker and Irmis, 2006).



6 comments:

  1. Psudopalatus jablonskiae isn't the lowest known Pseudopalatus in PEFO, although it is one of the lowest; there are more typically knobby P. buceros/P. pristinus looking squamosals from somewhat lower in the section. The supposed overlap between Adamanian and Revueltian faunas is about to disappear too, stay tuned me and Bill's paper in the dinosaur origins volume...

    Those Pseudopalatus drawings are pretty sweet, by the way.

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  2. Jeff Martz is correct. When the Parker and Irmis (2006) paper was published, it was accepted that there was a three part division of the Sonsela Member. Recent revisions by Jeff and I (Martz and Parker 2010) have shown that it is actually a five part division. These revisions have moved the biostratigraphic position of P. jablonskiae upwards so it is no longer the lowest occurrence. Having your local stratigraphy right is pretty important!

    As he stated we have an in press paper fixing all of the biostratigraphy in the Chinle Formation (mostly based on Petrified Forest National Park).

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  3. Hi,
    Nice information posted here... Really very interesting. The way of explaining is really good.Thanks for posting...

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  4. I probably don't have the most recent papers. I should have done some more searching before I wrote this, but I wanted to get a post up and things have been a little crazy (just moved).

    And Jeff, I just realized that I forgot to give you credit for the first image. I will amend that.

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  5. Susan,

    You don't have the most recent paper because it is still in press ;). Should be out soon as part of a big volume with all of the papers from the 2009 early dinosaurs sympsium at the SVP meeting in Bristol.

    Bill

    P.S. 3rd comment on this post is spam.

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  6. Although I am purely an amateur, I love the study of paleontology and entomology. We would love to have you folks posts studies on our Seymouria paleontology Yahoo Group sometime. We are at http://tech.groups.yahoo.com/group/seymouria/?yguid=321995096

    ReplyDelete