The current issue of Palaeontologia Electronica contains an article by myself and Bronson Barton describing some new material of the enigmatic archosauriform Vancleavea campi from Petrified Forest National Park. First off a disclaimer, it is no secret that two well-preserved skeletons from the Coelophysis quarry at Ghost Ranch New Mexico have been assigned to Vancleavea and are currently being described by Sterling Nesbitt, Michelle Stocker, Bryan Small, and Alex Downs. This new paper does not figure or discuss that material, and therefore does not contain the awaited reconstruction of this interesting animal. Instead this paper describes two partial skeletons from Petrified Forest National Park which contain postcrania not preserved in the holotype, discusses taxonomic issues, and provides a tentative phylogenetic analysis.
Vancleavea campi was named by Long and Murry (1995) based on a very fragmentary postcranial skeleton from the Upper Triassic Chinle Formation (Blue Mesa Member) of Petrified Forest National Park. Because of the incomplete nature of the material, Long and Murry (1995) could only assign the taxon to Neodiapsida incertae sedis. However, the taxon can be diagnosed by the presence of its characteristic osteoderms (see photo to the left) Additional material, including the Ghost Ranch specimens, was assigned to Vancleavea by Hunt et al. (2002) and Hunt et al. (2005) including additional material from near Stinking Springs in Arizona (Blue Mesa Member, Chinle Formation) assigned to a neodiapsid similar to Vancleavea by Polcyn et al. (2002). In addition, two partial skeletons were collected in 2004 from the Petrified Forest Member (Chinle Formation) of Petrified Forest National Park (Parker and Irmis, 2005). Subsequently, one of these specimens was the focus of a senior thesis by Bronson Barton and both are described in the new paper.
The tentative phylogenetic analysis suggests that Vancleavea campi is a derived non-archosaurian archosauriform. This is based mainly of the morphology of the femur (see photo bottom left) which has a sigmoidal shaft, distinct head, and lacks a intertrochanteric fossa. A very autopomorphic feature of Vancleavea is the morphology of the ilium (see photo bottom right) which differs significantly from that of all other known archosauriform taxa. In fact, the ilium of Vancleavea most superficially resembles that of drepanosaurid archosauromorphs.
Why is this new description necessary, especially when better material (i.e., the Ghost Ranch specimens) exists? Because the original type materials are so scrappy, it is important to supplement the type material with additional material from Petrified Forest National Park. Furthermore, if none of the new specimens (including the Ghost Ranch and Stinking Springs material) differ from the type material, yet differ from each other, then the type materials are nondiagnostic and the name Vancleavea would be a nomen dubium (Parker and Irmis, 2005). Thus, the description of this new material begins this process and is intended to provide future workers some tools to provide more detailed comparisons and to better determine the taxonomic status of the name Vancleavea.
Hunt, A.P., Lucas, S.G., and Spielmann, J.A. 2005. The holotype specimen of Vancleavea campi from Petrified Forest National Park, Arizona, with notes on the taxonomy and distribution of the taxon. New Mexico Museum of Natural History and Science Bulletin , 29:59-66.
Hunt, A.P., Heckert, A.B., Lucas, S.G., and Downs, A. 2002. The distribution of the enigmatic reptile Vancleavea in the Upper Triassic Chinle Group of the western United States. New Mexico Museum of Natural History and Science Bulletin , 21:269-273.
Long, R.A. and Murry, P.A. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science Bulletin , 4:1-254.
Parker, W.G. and Irmis, R.B. 2005. Advances in Late Triassic vertebrate paleontology based on new material from Petrified Forest National Park, Arizona. New Mexico Museum of Natural History and Science Bulletin , 29:45-58.
Polcyn, M.J., Winkler, D.A., Jacobs, L.L., and Newman, K. 2002. Fossil occurrences and structural disturbance in the Triassic Chinle Formation at North Stinking Springs Mountain near St. Johns, Arizona. New Mexico Museum of Natural History and Science Bulletin , 21:43-49.
In vino veritas
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