A STATISTICAL EXAMINATION OF THE ASAPHID TRILOBITE AULACOPARIA HUYGENAE FROM THE JOSÉ FORMATION OF SOUTHERN NEW MEXICO

The Lower Ordovician Jose Formation is a unique medium gray, oolitic limestone within the El Paso Group. To date, only the asaphid Aulacoparia huygenae Flower, 1968, has been described from the Jose. Due to the relatively effaced nature of the asaphids a biometrical examination of A. huygenae was undertaken to confirm the species’ identification. Large collections of asaphids were made from the Big Hatchet Mountains and the type locality at Cooks Peak. Smaller numbers of individuals were recovered from additional collections in the Florida and Caballos Mountains.

Initial studies were based upon the more abundant pygidia. Bivariate plots of 1) pygidial width as a function of pygidal length and 2) axial length as a function of pygidial length were prepared with regression lines computed for each individual locality. Comparison of these regression lines using Student’s t-test (Zar, 1999) showed no statistical differences and suggests the presence of only 1 species. Further, measurements of the illustrated type pygidia plotted with the available specimens. A further comparison to 2 other asaphid species suggested that, given the species available, axial length was able to resolve individual species while pygidial width did not. The less common cranidia are commonly fragmentary frustrating any statistical analysis.