Morphometric investigation of the Pentremites fauna from the Glen Dean Formation, Kentucky

New techniques involving three-dimensional (3D) data collection and landmark analysis provide an opportunity to make breakthroughs in understanding blastoid morphology. This pilot study examines four species (Pentremites pyriformis, P. tulipiformis, P. fredericki n. sp., and P. meganae n. sp.), using 3D morphological variation and geometric morphometrics to discriminate between species. All specimens were collected from a single shale unit within the Upper Mississippian Glen Dean Formation near Hopkinsville, Kentucky. A 3D laser scanner was used to acquire 3D images for all specimens. Conservative blastoid thecal plating allowed the collection of 3D coordinates for a series of homologous landmarks from these laser images that fully describe specimen morphology. Data were analyzed using the R (language and environment for statistical computing and graphics) packages SHAPES and MCLUST. Mixture modeling identified and separated all four species based on shape alone. In addition, three new ...