Standardization of the Anatomical Orientation of Receptaculitids

Abstract

Much of the controversy that has surrounded the study of receptaculitids has been associated, in one way or another, with difficulties in reconstructing their mode of growth. Many of these difficulties, in turn, result from inadequate comparative morphological analysis and a consequent ambiguity in relating the results of work on one taxon to arguments framed in the context of another. In order to deal with this aspect of the controversy, we propose a standardization of anatomical orientation for receptaculitids, based on features that we argue are homologous, taxonomically widespread, and useful as criteria of polarity. These include: overall thallus shape; morphology and arrangement of intercalary meroms; latitudinal gradients in number of meroms per whorl; articular relationships of stellate structures; and imbrication of merom plates. This standardization will contribute to an understanding of growth and life orientation in receptaculitids by acting as an arbiter of the consistency of growth analyses performed on morphologically disparate taxa.