Quantitative analysis strengthens qualitative assessment: a case study of Devonian brachiopod species

Abstract

Species recognition attributed to the brachiopod family Atrypidae is evaluated based on qualitative and quantified morphological characters. I identified two brachiopod species—Pseudoatrypa lineata and Pseudoatrypa devoniana—from a rich assemblage of brachiopods recovered from the middle Devonian Genshaw Formation of the Traverse Group. Qualitative examination suggested that the former had fine-medium-sized ribbing, a narrow hinge line, widened anterior, moderately steep mid-anterior fold, domal shaped dorsal valve, and an inflated ventral valve in contrast to the coarse ribbing, widened hinge line, narrow anterior, gentle mid-anterior fold, arched-shape dorsal valve, and flat ventral valve of the latter. The shell outline appears rounded for P. lineata and elongated for P. devoniana. Quantitative assessment of the morphological characters on the dorsal, ventral, anterior, and posterior regions of the valves of the two species using geometric morphometric and statistical analyses suggests that the morphologies of the two species are considerably different (P \( \ll \) 0.01). Thus, qualitative differences between the two atrypid species were further corroborated by quantitative results. This emphasizes the fact that these two species of Pseudoatrypa were indeed different from each other. This study highlights the necessity of incorporating quantified morphological characters to successfully investigate the taxonomic distinctness of fossil invertebrates to the species level.