Morphometric Analysis of Two Eocene Related Radiolarian Species of the Podocyrtis (Lampterium) Lineage

Abstract. A metric analysis of the morphology of two related Eocene species (Podocyrtis sinuosa and P. mitra) that are part of the Lampterium evolutionary lineage was undertaken in order to evaluate hypotheses related to their mutual taxonomic distinction statistically. All analyses (landmark, outline semi-landmark and landmark-constrained outlines) support an interpretation of statistically significant species-specific shape differences. Moreover, landmark and semilandmark-based morphometric characterizations can be used to identify which regions of the test are best suited for making reliable taxonomic distinctions. These results suggest that both abdomen and thorax shapes represent species-specific characters. While this agrees, in part, with previous, qualitative diagnoses, our results shed light on precisely how abdomen and thorax shape differ between these species. In addition, our investigation demonstrates the taxonomic value of a morphometric approach to character analysis as thorax shape differences had gone unnoticed by previous investigators.