A Revueltian (Norian) phytosaur from the Sonsela Member of the Petrified Forest Formation (Chinle Group: Upper Triassic), Petrified Forest National Park, Arizona

ASU Author/Contributor (non-ASU co-authors, if there are any, appear on document)
Andrew B. Heckert Ph.D., Assistant Professor of Geology (Creator)
Institution
Appalachian State University (ASU )
Web Site: http://www.library.appstate.edu/

Abstract: The Sonsela Member of the Petrified Forest Formation (Upper Triassic) is widely exposed in northeastern Arizona and northwestern New Mexico. Fossil wood is common in the fluvial Sonsela, but the high energy depositional conditions appear to have destroyed all fossil bone except for small fragments. The first identifiable vertebrate fossil from channel-facies of this unit is an incomplete phytosaur skull preserved on a fallen block of sandstone on a cliff in the Rainbow Forest area of Petrified Forest National Park, Arizona. This cliff is "Flattops Sandstone I," which we consider to represent the upper part of the Sonsela Member. The left side of the skull, lacking the anterior half of the rostrum, is preserved in lateral view. The specimen is uncollectable, but casts are preserved at Mesalands Dinosaur Museum, Petrified Forest National Park, and the New Mexico Museum of Natural History and Science. The two most important morphological features of this specimen are: (1) the external nares are at approximately the same level as the skull deck; and (2) the posterior squamosal process in lateral view is narrow and not pendulous. This combination of features is diagnostic of the genus Nicrosaurus. The only other published account of Nicrosaurus in North America is Nicrosaurus buceros from the Chama basin of north-central New Mexico. The common Nicrosaurus kapffi and the rare N. meyeri occur in the Norian Stubensandstein of southwestern Germany. This specimen is biochronologically sig:p.ificant as it demonstrates that the Sonsela is indeed Norian in age, as has been suggested previously. Paleobiogeographically, it is one of an increasing number of Late Triassic tetrapod taxa that were previously thought to be exclusively European in distribution (e.g., Erpetosuchus, Aetosaurus, Stagonolepis) that have now been identified in North America.

Additional Information

Publication
Hunt, A.P., Lucas, S.G., and Heckert, A.B., (2002) A Revueltian (Norian) phytosaur from the Sonsela Member of the Petrified Forest Formation (Chinle Group: Upper Triassic), Petrified Forest National Park, Arizona. New Mexico Museum of Natural History and Science Bulletin 21, 165-169. (ISSN 1524-4156) Archived in NC DOCKS with permission of the editor. The version of record is available at: http://econtent.unm.edu/
Language: English
Date: 2003