Field of Science

The Osteology and Relationships of Vancleavea campi (Reptilia: Archosauriformes)

Um...OK, this came out a bit earlier than I expected and is now available online from the Journal of the Linnaean Society. This is the long awaited full description of this taxon, which supersedes my 2008 publication which came out when this paper was in press and therefore not cited. Sterling felt that the new PEFO material should be dealt with in a separate publication, but unfortunately I did not get it out in time for him to use, and to ask him and his coauthors to go back through this manuscript in the proof stages and add info from my paper would have been too much. So we are left with a weird case in which two papers come out on the same taxon and neither cite each other, but I assure you that we were all aware of each other's work before anyone questions ethics. Sterling did compare the GR material to one of the PEFO specimens; whereas I did not describe or code any of the Ghost Ranch material, thus this new paper is up to date in that regard.

I guarantee you that this is one of the most bizarre archosauriforms you may ever encounter, see the above reconstruction courtesy of Sterling Nesbitt. Enigmatic since its initial discovery in 1962 (from Petrified Forest National Park) and initial description by Long and Murry in 1995, recent collection of better specimens has elucidated its osteology and broader relationships. Vancleavea is actually common at most levels of the Chinle Formation; however, due to the scrappy nature of most of the materials it is difficult to compare specimens across stratigraphic levels. Are we looking at one species or several? I congratulate Sterling, Michelle, Bryan, and Alex on a great discovery and paper.

Nesbitt, S. J., Stocker, M. R., Small, B. J., and A. Downs. 2009. The osteology and relationships of Vancleavea campi(Reptilia: Archosauriformes). Zoological Journal of the Linnaean Society 157:814–864 doi: 10.1111/j.1096-3642.2009.00530.x

Vancleavea campi Long & Murry, 1995, from the Late Triassic of western North America, represents the latest surviving non-archosaurian archosauriform known to date. We present here a detailed comparative description based on a nearly complete, articulated skeleton from the Coelophysis Quarry in north-central New Mexico and other fragmentary specimens. The unique combination of morphological features of Vancleavea is unparalleled within Reptilia; it has four unique morphologies of imbricated osteoderms covering the entire body, a short, highly ossified skull, relatively small limbs and morphological features consistent with a semi-aquatic lifestyle. Vancleavea is placed in a rigorous phylogenetic analysis examining the relationships of non-archosaurian archosauriforms, and is found to be more closely related to Archosauria than both Erythrosuchus and Proterosuchus, but outside of the crown group. The analysis confirms previously hypothesized relationships, which found Euparkeria to be the closest sister taxon of Archosauria. It is not clear whether specimens referred to Vancleavea campi represent a single species-level taxon or a clade of closely related taxa that lived through much of the Late Triassic of North America, given the poor fossil record of the taxon.

8 comments:

  1. What an interesting specimen--I'd never heard of it. It's nice to have your hypotheses confirmed. Thanks for posting.

    I have to learn more about the Ghost Ranch, too. I suppose Georgia O'Keefe never painted any fossils?

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  2. Bill, are you going to tackle the single or multiple species issue?

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  3. Bryan - I don't think its possible to do much more on the single/multiple species issue than you and Sterling et al. have done in the new paper. Right now its not possible to say much on this topic until we discover more complete material from different localities from older statigraphic levels.

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  4. Bryan,

    As Randy has stated, there does not seem to be too much variation between the different known specimens that can be considered to be due to taxonomic differences. That said, because Vancleavea has such a long range I'd be surprised if V. campi was that long lived, but it will take more well-preserved specimens from a variety of levels to test this.

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  5. Curious...

    Why did you restrict your inclusion set to those 12 taxa? When I placed data from your new description into a larger analysis covering the gamut of the Amniota Vancleavea nested outside of the 12. And, contrary to my earlier postulate that Vancleavea might be related to Cerritosaurus, that is also an error. I sent Alex my tree and some further notes. Get with him and then we should discuss this.

    David Peters

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  6. What I had in mind in my previous post was the SMU material. I assume it is older than the Ghost Ranch material and was under the impression that there was quite a bit of it. Will it be published?

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  7. Bryan: Both Sterling and I have seen the SMU Vancleavea material. But, it is being worked on by SMU folks, so that is why Sterling couldn't mention it in the paper. There is a decent amount of material with the specimen.

    David: you should ask the authors that question; Bill was not an author of the Nesbitt et al. 2009 paper.

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  8. I still think that Vancleavea looks like a hatchling Rhedosaurus: The Beast from 20,000 Fathoms.

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