MORPH-ECOSPACE OCCUPATION IN PALEOZOIC RHYCHONELLIFORM BRACHIOPODS: AN EXPLORATION THROUGH SPACE AND TIME

Brachiopod shell morphology is well characterized descriptively based on valve shapes, but is poorly integrated in a scheme that allows for quantitative comparison across disparate forms. A focus on overall variation of valve morphology, independent of taxonomic classification, provides an avenue to define a morpho-ecospace and relative disparity within the phylum. From this, morpho-ecospace and distributional patterns of other factors can be compared, (e.g., environmental, phylogenetic, paleobiogeographic). This study aims to provide a standardized way in which to document morphologic variation in overall shell form of all know articulate brachiopod groups, in a systematic manner by placing forms in a concise multivariate morpho-ecospace. We evaluated multiple approaches to defining a brachiopod shell morphospace (e.g. traditionally defined characters, investigation of novel derived characters, and detailed landmark shape analysis). Our defined morphospace is based on a limited number of 2-D landmarks taken independently from dorsal and sagittal shell outlines and a series of size-standardized linear distance characters (e.g. max length, mid-shell width, etc.) were calculated from Procrustes transformed landmarks for both dorsal and sagittal orientations and combined into a single data set of nine characters per genus-level OTUs. Principal component space based on these data provides a context for qualitative and quantitative comparison of dorsal and sagittal shell morphology in similar and disparate brachiopods. Categorical data, e.g. presence-absence of features, are integrated with results of PCA to refine the morphospace. In an initial test of the methodology, we are applying it to an evaluation of the morpho-ecospace occupation of the late Ordovician Richmondian invasion of the Cincinnati region brachiopod fauna based on work of Stigall and others. These methods have further implications for broader studies of evolution, migration events, biogeographic distribution, and concepts surrounding ecological niches.