A giant skull, ontogenetic variation and taxonomic validity of the Late Triassic phytosaur Parasuchus

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: Parasuchus (= Paleorhinus) is the most primitive known phytosaur, and its fossils define a Carnian biochron recognizable across much of Pangea. The largest known specimen of this primitive taxon, an incomplete skull from the Popo Agie Formation in northwestern Wyoming, demonstrates that the nares remain anterior to the antorbital fenestra throughout the ontogeny of Parasuchus, an observation confirmed by an analysis of a broad database. The fact that this character is not variable through the ontogeny of this phytosaur genus, as some previous authors have speculated, helps to cement the taxonomic validity of Parasuchus. For the past century, systematists have attempted to establish a classification of organisms rooted in some form of a biological species concept. Cladotaxonomy, on the other hand, is the recognition of cladotaxa, which are low-level taxa (genera and species) that correspond to clades in a cladistic analysis. Cladotaxonomic relegation of all primitive phytosaurs to a metataxon is based on a posteriori evaluation of character polarity that fails to acknowledge the existence of a biotaxon regardless of how a cladist evaluates character polarities millions of years later. We reject assignment of primitive phytosaurs to a metataxon as uninformative, and recognize Parasuchus as a diagnosable phytosaur genus.

Additional Information

Publication
Lucas, S. G., Heckert, A. B., and Rinehart, L. F., (2007) A giant skull, ontogenetic variation and taxonomic validity of the Late Triassic phytosaur Parasuchus: New Mexico Museum of Natural History and Science Bulletin, v. 41 (The Global Triassic), p. 219-221. Archived in NC DOCKS with permission of the editor. The version of record is available at: http://econtent.unm.edu/
Language: English
Date: 2007