The vertebrate assemblage of the Late Triassic Canjilon Quarry and the importance of apomorphy based assemblage comparisons

Nesbitt, S.J., and M.R. Stocker. 2008. The vertebrate assemblage of the Late Triassic Canjilon Quarry (Northern New Mexico, USA) and the importance of apomorphy based assemblage comparisons. Journal of Vertebrate Paleontology 28:1063-1072.

ABSTRACT—The Upper Triassic Canjilon Quarry in northern New Mexico preserves a vertebrate assemblage typical of the Norian Stage of North America. Although dominated in relative abundance by the phytosaur Pseudopalatus and the aetosaur Typothorax, a more diverse assemblage of smaller forms was previously reported. Additions to the Canjilon
Quarry vertebrate assemblage are critically reviewed and described using an apomorphy-based method for assigning taxa. An apomorphy-based approach for compiling and comparing assemblages allows each taxonomic assignment to be a testable hypothesis. Fragmentary yet diagnostic elements that may not be assignable to a species-level taxon can be assigned to a larger clade and thus provide useful information. Additionally, each taxon listed in the assemblage must be tied to a diagnostic specimen listed with a museum specimen number. Using this method for the Canjilon Quarry, we establish the presence of an assemblage that is more similar to other vertebrate quarries near Ghost Ranch than previously thought. The Canjilon Quarry assemblage is restricted to vertebrates from UCMP locality V2816. Vertebrate material housed at the Museum of Comparative Zoology, Harvard, which was reported from the Canjilon Quarry, was not collected from UCMP V2816 but from a nearby locality.

The Canjilon Quarry from the Petrified Forest Member (Chinle Formation) of New Mexico was mainly worked by Charles Camp and crew (University of California, Berkeley) in 1933 and produced a wealth of fossil vertebrate material, most notably numerous skeletons (including a suite of skulls) of the phytosaur Pseudopalatus. You can get more information on the Canjilon Quarry, including an extremely detailed reconstruction of the 1933 excavation from field notes, here and here. Of course the main point and overall importance of this paper is the discussion on using apomorphy based identifications when creating faunal lists.