USING DIVERSE APPROACHES TO RESOLVE A LATE CAMBRIAN FAUNAL ASSEMBLAGE FROM THAILAND

The Cambrian is widely recognized as having high rates of evolutionary diversification. With rapid evolution of relatively short-lived species and genera and numerous species with notable intraspecific variation, differentiating taxa based on a morphological species concept of consistently diagnosable characters is often challenging. Phylogenetic and morphometric tools can help in delineating and grouping taxa and were recently used on challenging new material from the late Cambrian Tarutao Group of southern Thailand. Cladistic analysis has helped us assign a new genus, Satunarcus, to the family Kaolishaniidae, and to recognize a new subfamily, Ceronocarinae, therein. Landmark-based morphometric analysis has helped differentiate generic differences between Thailandium and Prosaukia, as well as to determine the extent of intraspecific variation in Eosaukia buravasi Kobayashi, Quadraticephalus planulatus (Kobayashi), and Haniwa sosanensis Kobayashi. While cladistics can be a powerful tool for understanding taxonomic relationships it requires that constituent species are well-resolved in order to select characters that have potential phylogenetic signal. Running analyses is also very time consuming. Morphometric analysis can readily be applied to collections with unresolved taxonomy provided that specimens are sufficiently preserved for a representative set of landmarks and of sufficient overall similarity to be described by a single landmark scheme. When applied to the Tarutao fauna, both tools proved useful in determining which characteristics may be diagnostic in differentiating taxa, though morphometric analysis has the additional benefit of being able to identify characters previously overlooked. This was particularly useful in the case of Thailandium vs Prosaukia in which facial suture convergence, a previously overlooked character, was determined to significantly contribute to discreet morphological groupings. Well-resolved, consistent taxonomy is a prerequisite for biostratigraphy, paleogeography, and biodiversity studies, and we found the benefits to taxonomic resolution well worth the time commitment in such statistical approaches.