WHAT EXTERNAL MORPHOLOGY OF RHYNCHONELLIFORMEA BRACHIOPODS CAN TELL US: NEW QUANTITATIVE METHODS FOR SHELL SHAPE CHARACTERIZATION APPLIED TO THE LATE ORDOVICIAN RICHMONDIAN INVASION

Rhynchonelliformea Brachiopoda is one of the most well-documented and studied groups of invertebrate organisms in the fossil record, but the current lack of standardized methods for comprehensive analyses of shell shape allows for important aspects of brachiopod life to be disregarded. Context dependent studies that are taxonomically, temporally, or geographically restricted are significant within their field and fail to address larger questions about the total external morphology. The Seven-C approach, defined as “Consistent, Comparable, Comprehensive, Concise Characterization of shell form for Communication and Consideration” provides the tools for studying the morphological aspects of topics including ontogeny, paleobiogeographic distribution, niche tolerance, intrageneric variation, phylogenetics, and functional morphology in multidimensional space using multivarsiate data analysis. This new approach is composed of a hierarchical numerical coding system of characters and character states which are broadly encompassing aspects of external brachiopod morphology that are either measured, observed, or scaled and then analyzed as singular characters and an entire descriptive summary of shell shape. To test the viability and efficiency of the new method, the Seven-C Approach was applied to 49 brachiopod species described in Stigall (2010)’s study on the niche tolerance as interpreted from the paleobiogeographic distribution and range of Cincinnati Arch rhynchonelliform brachiopods to observe potential morphological patterns between and among species through space and time. Principal component and canonical variance analyses produced results that highlight a notable morphological similarity between specialist locally extinct species and the invasive generalist species that later fill in the niche in the Cincinnati Arch as well as at distinguish morphological characters that determine generic and familial level similarities which successfully establishes the Seven-C Approach as viable for simplifying current brachiopod morphological terms for clearer and more accessible communication with quantitative applications.