PHYLOGENETIC ANALYSIS OF LATE ORDOVICIAN NORTH AMERICAN BATHYURID TRILOBITE GENERA RAYMONDITES AND BATHYURUS

The youngest genera of Late Ordovician bathyurid trilobites, Raymondites and Bathyurus have a rich history of study, but suffer from a lack of recent systematic or phylogenetic analysis, especially for Raymondites. These taxa occur in Late Ordovician, Mohawkian (Sandbian-Kaitian) strata of North America (Laurentia) during a period of significant paleoenvironmental shifts, due to the onset of the Taconic orogeny and global climate cooling (GICE excursion). Systematic and phylogenetic studies of these genera and others from this time provides a framework for better understanding evolutionary trends during times of dramatic environmental shifts.

While a number of species are currently known for Raymondites systematic work has been complicated by the relative rareness of material. R. bandifer is only known from its holotype, while other members are often represented by material in poor condition, with limited quantities available. The goal of this study is to revise Raymondites to broaden the understanding of family Bathyuridae by placing the genus into a phylogenetic context with Bathyurus and provide a better understanding of their evolutionary history. This revision re-examines the current Raymondites material and includes previously undescribed material from the Royal Ontario Museum, Toronto, Ontario, Canada (ROM) and a new Raymondites species from the Kimmswick Limestone, Mo. For this study a phylogenetic analysis was conducted using parsimony analysis from a character state matrix compiled from data on cranidium, librigena, and pygidium character states. Results from the analysis support a monophyletic Raymondites clade while Bathyurus is interpreted to form a paraphyletic clade. Raymondites is distinguished by: 1) a reduced palpebral length vs. glabella length ratio, 2) elongate genal spines, 3) expanded lateral and anterior margins, 4) occipital and axial pygidial spines in the majority of members.