The order Fenestrata (Bryozoa) of the Toroweap Formation (Permian), southern Nevada

Abstract

Recently developed analytical procedures for meshwork fenestrate and pinnate bryozoans made it possible to recognize two Russian species in the Toroweap Formation of southern Nevada. This analysis separates zoarial and zooecial features and emphasizes the three-dimensional form and size of the zooecial chamber as well as accessory features. In this investigation, these analytical procedures are successful even when specimens are fragmented and embedded in a hard rock matrix.The bryozoans in the Toroweap Formation in this study were found to be more similar to Permian species of the Russian platform than to species described in earlier North American Permian studies. Five species of fenestrate bryozoans are present in the Toroweap Formation. Wjatkella permiana Morozova, 1970, and Polypora sargaensis Trizna, 1948, originally described in Russia, are recognized in the Toroweap. Three new species, Penniretepora oppositus n. sp., Septopora bilateralis n. sp., and Reteporidra anaphora n. sp., are present and, along with the Russian species, are described in this paper.The local range zones of the five species of fenestrates were identified in three measured sections. Penniretepora oppositus and Septopora bilateralis are present throughout the three sections; Reteporidra anaphora is present in the lower two-thirds of the three sections; Wjatkella permiana is present in the middle parts of the three sections; and Polypora sargaensis is present in the upper parts of the three sections. Concurrent range zones, based on ramose bryozoans, were previously identified in two of the three sections and, using the distribution of the fenestrates in these two sections, four of the five concurrent range zones were recognized in the third section.