Taxonomy, Functional Morphology and Paleoecology of the Fenestellidae and Polyporiidae (Fenestelloidea, Bryozoa) of the Warsaw Formation (Valmeyeran, Mississippian) of the Mississippi Valley

Abstract

Fenestellid and polyporid Bryozoa of the Lower Mississippian Warsaw Formation of the Mississippi River outcrop belt are represented by nine genera of Fenestellidae (three of which are new--Banastella, Cubifenestella, and Apertostella) and two genera of Polyporidae. Twenty-two previously described and fifteen new species are recognized. New species are Laxifenestella coniunctistyla, Laxifenestella maculasimilis, Laxifenestella fluctuata, Minilya sivonella, Minilya paratriserialis, Banastella guensburgei, Banastella mediocreforma, Banastella delicata, Cubifenestella usitata, Cubifenestella globodensata, Apertostella foramenmajor, Apertostella crassata, Apertostella venusta, Hemitrypa aprilae, and Archimedes valmeyeri.

Exterior and interior analyses of bryozoan zoaria are employed, separating zoarial and zooecial features and emphasizing three-dimensional form, chamber size, and accessory features.

An ecologic succession of four stages is present in the Warsaw. Initial stabilization of carbonate and clastic mud bottoms by meshwork fenestrate Bryozoa (pioneering stage) was followed by a sequence marked by increasingly massive forms, culminating with extremely massive, encrusting forms in the climax stage.

Using modern cheilostomes as an analog, possible niche differentiation of meshwork fenestrates was based on chamber volume, lophophore diameter, mouth diameter, inferred maximum zooid clearance rate, inferred tentacle number, and tentacle length. These criteria, food particle size and efficiency of the feeding organ (lophophore) are dominant agents governing niche partitioning among meshwork fenestrates.

Change of meshwork fenestrate species composition within the Warsaw from north to south within the study are could have been caused by environment or evolution.