Discrimination of fenestrate bryozoan genera in morphospace

Steven J. Hageman and Frank K. McKinney

Abstract

Concepts for generic diagnoses and discrimination of biserial fenestrate Bryozoa (Fenestellidae) have varied historically, but have largely been based on specialized colony forms (e.g., Archimedes), the shape and budding arrangement of chambers and other internal skeletal features such as hemisepta, and occasionally on the presence or absence of discrete characters, such as placement of nodes on the frontal surface (e.g., Minilya). The question remains as to whether biserial fenestrate genera represent real biological clades, or whether they are convenient groupings of morphotypes based on untested characters. This study evaluates the distribution of 1075 operational taxonomic units (OTUs) from 15 fenestrate genera with measurements for nine morphometric characters – external features are not emphasized in most generic diagnoses. Here, each OTU represents a composite or idealized individual from a colony. Results show that OTUs plotted in principal component space do largely form coherent clusters based on a priori generic assignments. Thus the groupings based on characters other than the ones used to originally define them, add support to the notion of biological significance for recognized genera. The exceptions actually highlight and help resolve known issues. Therefore, we recognize Alternifenestella as a junior synonym of the genus Spinofenestella, and propose reassignment of Laxifenestella serratula in Snyder (1991) to Fenestella serratula, and Fenestella sp. 1 in Ernst and Schroeder (2007) as Rectifenestella. We do not advocate that biserial fenestrate generic concepts should be based on the nine external characters used in this study, but rather that they can be used independently to evaluate the coherence of genera based on other discrete characters.

Steven J. Hageman. Department of Geology, Appalachian State University, Boone, NC 28608, USA
Frank K. McKinney. Department of Geology, Appalachian State University, Boone, NC 28608, USA

Key Words: Bryozoa; Fenestrata; taxonomy; morphology; three-dimensional

PE Article Number: 13.2.7A
Copyright: Paleontological Society July 2010
Submission: 21 July 2009. Acceptance: 27 January 2010