A new morphometric model in distinguishing two closely related extinct brachiopod species

Abstract

Pseudoatrypa (Atrypida, Brachiopoda) are extinct Paleozoic brachiopods that are the closest relatives of the modern brachiopods, rhynchonellids. Two Paleozoic brachiopod species were qualitatively distinguished based on close examination of phenotypic characters and traditional morphometrics. These species were recovered for the first time from the Givetian localities of Traverse Group of Michigan. The efficacy of geometric morphometric analyses in discriminating species has been proven for various organisms, but rarely studies have been performed in distinguishing brachiopod species. The advanced morphometric model developed here using the Procrustes-based landmark method is based on the analysis of valve shape in two extinct brachiopod species: Pseudoatrypa lineata and Pseudoatrypa devoniana. Results from quantitative analyses reinforce the qualitative identifications of the two species. The application of this method on four different orientations (dorsal, ventral, posterior and anterior regions) of the brachiopods permits the two species to be clearly separated, and this study proposes that the model can be effectively used for future identification and distinction of fossil species. Additionally, this study will aid biologists, paleontologists and neontologists in making appropriate advancement in systematic studies and further assist with gauging biodiversity congruously.

Keywords:

• Atrypida
• Givetian
• Traverse
• morphology
• Procrustes
• Paleozoic

Acknowledgements

This research was funded by the Theodore Roosevelt Memorial Research Grant received from the American Museum of Natural History. I would especially like to thank Alex Bartholomew for providing stratigraphic information of the Traverse Group of Michigan Basin and for providing access to his brachiopod collections, which are now reposited at the Indiana University Paleontology Collections. I would also like to acknowledge insightful discussions on atrypid morphology with Jed Day from Illinois State University, brachiopod paleoecology with Chris Schneider from Alberta Geological Survey and Claudia Johnson from Indiana University, and morphometrics with David Polly from Indiana University and Lindsey Leighton from University of Alberta. I would also like to express my gratitude to Erle Kauffman for suggestions on qualitative study of the brachiopod specimens. My sincere thanks to Arnab De from Columbia University for stimulating discussions on this topic.