APPLICATION OF MORPHOMETRIC TECHNIQUES TO ICHNOFOSSILS: A CASE STUDY OF RUSOPHYCUS FROM THE MIDDLE CAMBRIAN GROS VENTRE FORMATION, WYOMING, USA

Attempts to apply morphometric techniques to trace fossils, and thereby create reproducible and objective ichnotaxabases, are usually thwarted by small sample sizes of the ichnotaxon under study. An ichnological lagerstätte of Rusophycus (trilobite trace fossil) from the Middle Cambrian Gros Ventre Formation of Wyoming, USA, provided a large enough sample size to attempt biometric analysis of this ichnofauna. We initially defined and measured 12 distances between landmarks, 3 angles, and 4 counts of morphologic characters from 117 specimens of Rusophycus from the Gros Ventre. Distance metrics were transformed to reflect shape rather than size. Two meristic characters were retained, and the resulting 14 characters were standardized to give all values a range between 0 and 1. Multivariate analyses were performed using PAST (PAleontological STatistics). Results of an initial analysis using Ward Euclidean clustering were reconciled with qualitative examination of the specimens, which indicated that numerous incomplete or poorly preserved traces were inconsistently classified. As a result, the specimen base was culled and the number of specimens judged useful for morphometric analysis was reduced from 117 to 50. Poor or variable preservation remains an intractable problem in attempting to apply quantitative measures in the definition of ichnotaxa (many which are based on a single specimen). The most useful diagnostic criteria for distinguishing Rusophycus ichnogenera are overall shape, and the presence of unique morphologic features.

(Additional co-authors include CANNELL, Emily, COOPER, Tara, DAVIS, Sarah, HENDERSON, Lauren, HOFFMAN, Alice, LAZZARI, Andrea, SAUNDERS, Kristen, SUING, Kristen, and ZIELINSKI, Victoria, Michigan State University, East Lansing, MI 48824)