Palaeontologia Electronica http://palaeo-electronica.org 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 pres- ence or absence of discrete characters, such as placement of nodes on the frontal sur- face (e.g., Minilya). The question remains as to whether biserial fenestrate genera represent real biological clades, or whether they are convenient groupings of morpho- types 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 col- ony. 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 syn- onym of the genus Spinofenestella, and propose reassignment of Laxifenestella serrat- ula 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. [email protected] Frank K. McKinney. Department of Geology, Appalachian State University, Boone, NC 28608, USA. [email protected] KEY WORDS: Bryozoa; Fenestrata; taxonomy; morphology; three-dimensional Editorial note: animations are visible at palaeo-electronica.org/2010_2/206 PE Article Number: 13.2.7A Copyright: Paleontological Society July 2010 Submission: 21 July 2009. Acceptance: 27 January 2010 Hageman, Steven J., and McKinney, Frank K., 2010. Discrimination of Fenestrate Bryozoan Genera in Morphospace. Palaeontologia Electronica Vol. 13, Issue 2; 7A: 43p; http://palaeo-electronica.org/2010_2/206/index.html HAGEMAN & MCKINNEY: FENESTRATE MORPHOSPACE INTRODUCTION by dichotomous division of the growing tip of the branch or by lateral branches (pinnae) that formed The purpose of this study is to use characters on the sides of the parent branch just behind the visible from the exterior of biserial fenestrates to growing tip. These two types of branch multiplica- define morphospace occupied by observed taxo- th nomic units (OTUs) assigned to diverse genera tion were used from the late 19 century through th and to determine whether OTUs, assigned a priori most of the 20 century as the basis for the two to a given genus form a distinct cluster within a major taxonomic subdivisions of the fenestrate smaller region of that morphospace. If there is little bryozoan clade (e.g., Bassler 1953), although or no clustering of OTUs assigned to a given genus recently some bryozoan taxonomists have empha- within the inclusive morphospace, the reality of sized other morphological characters that result in fenestellid genera based largely on internal charac- the mixing of branching types within families (e.g., ters might be more severely questioned, but dis- Morozova 2001). The focus of this study is biserial tinct clusters of OTUs belonging to those genera forms traditionally assigned to the family Fenestelli- supports their discrimination as morphologically dae. characterizable subgroups based on measurable Early Concepts of Fenestellid Genera. The first external morphological characteristics (Hageman genus of fenestrate bryozoans to be characterized 1991). in print was Archimedes, named by David Dale This is a study of genera. The existence of Owen in 1838 who (p. 13) referred to it only as “...a nominal species is acknowledged, but should be fossil, described by Lesueur under the name of considered in the context of within genus variation. Archimedes, on account of its screw-like form.”. The concept of fenestrate species distributions in The following year, Lonsdale (1839, p. 677) intro- morphospace will be treated elsewhere. duced the name Fenestella for, “A stony coral, fixed at the base and composed of branches, Historical Summary which unite by growth and form a cup. Externally In general, the characterization of genera is a the branches anastomose or regularly bifurcate; subjective enterprise. As more information accu- internally they form a network, the intervals being mulates, if morphological detail rather than gross generally oval, one row of pores on the branches morphology is considered more closely, some sup- externally, the openings being circular and project- posedly well-known genera begin to be reinter- ing when perfect. The branches, when regularly preted as a complex of related but distinguishable bifurcated, are connected by distant, transverse genera. The brachiopod genus Productus is one of processes, in which no projecting pores are visi- the better known examples, with 29 genera being ble.” named in a single volume based on type species The name Archimedes was used in print for originally described as a species of Productus solid helical structures a few times between 1838 (Muir-Wood and Cooper 1960). Fenestrate bryozo- and 1857, and several species were named from ans similarly experienced proliferation of generic around the world as Fenestella. In 1857 Hall (p. names during the late 20th century as formerly 177) recognized that Archimedes and Fenestella widely familiar, easily discriminated genera were are related and summarized their differences: “In subdivided. all essential characters, the foliate expansions of Fenestrate bryozoans are a major component Archimedes corresponds to Fenestella, according of the mid- to late Paleozoic marine fossil record. to the extended description of this genus by Mr. With one known exception, they are characterized Lonsdale; and in detached fragments cannot be by a shared colonial growth habit. They consist of distinguished generically from other forms of the rigidly erect, narrow branches in which all autozo- same genus....The mode of growth, therefore, con- oecia open toward one side of the branch (the stitutes the only reliable character for separating same direction as neighboring branches), and the Archimedes from Fenestella; and should this char- number of rows of autozooecial apertures along acter be hereafter considered of sufficient impor- the branch is limited, varying from two to about ten. tance, I propose to retain Le Sueur’s original name Branches typically are laterally linked by anasto- ‘Archimedes’. mosis, by skeletal bars (dissepiments) lacking John Phillips (1841) added a third genus, autozooecia, or by short lateral branches bearing Hemitrypa, to the Paleozoic fenestrates soon after autozooecia . Branch proliferation occurred either Archimedes and Fenestella were established. Phil- 2 PALAEO-ELECTRONICA.ORG lips (1841, p. 27) characterized Hemitrypa as “...a Monopora, which is constructed the same as in cup-formed mass; external surface wholly covered Fenestella but inaccurately described as branches with numerous round pores of cells...associated in with only a single row of zooecia.” double rows...The internal face was like that of The generic name Monopora Lebedev, 1924 some Fenestellæ, but the peculiarities of the exter- has been abandoned. In part, that is because Leb- nal surface seem to require generic separation.” edev’s original specimen has apparently been lost, The generic name Hemitrypa relates to Phillips’ and it is impossible to get a sense of zoarial or mistaken understanding that the fenestrules zooecial details from his description and illustra- extended from the internal surface only halfway tion. Nikiforova (1933b), in a study of bryozoans through the skeleton. He did not realize that the from the same region and stratigraphic level, reas- visible external surface was a superstructure con- signed Monopora donaica to Fenestella and sisting of a finer mesh than the branches, which named three subspecies, minor, media, and major. was developed as an integrated canopy above the Termier and Termier (1971) designated F. donaica branches by proliferation and fusion of lateral pro- (Lebedev) minor Nikiforova as type species of their cesses at the outer ends of long spines extending new genus Alternifenestella. Lebedev (1924) gave from the surface of the underlying branches. no scale for the single illustration of Monopora The first three genera of fenestrate bryozoans donaica, so it is not possible to make any decision to be characterized were fenestellids in the broad about which, if any, of the three subspecies named sense, i.e., branches increased by bifurcation by Nikiforova (1933b) may include Lebedevs spec- rather than developing as pinnae, were laterally imen. F. donaica (Lebedev) minor Nikiforova legiti- linked, and each contained two rows of autozooe- mately stands as type species of Alternifenestella.