The oldest bifoliate cystoporate and two other bryozoan taxa from the Dapingian (Middle Ordovician) of north-western Russia

Anna V. Koromyslova, Petr V. Fedorov

Research outputpeer-review

Abstract

Bryozoans from the Dapingian (Middle Ordovician) of the Baltic paleobasin remain poorly studied and their taxonomic composition is unclear. In this paper, three bryozoan taxa, a bifoliate cystoporate Planopora volkhovensis
n. gen. n. sp., a trepostome Hemiphragma insolitum n. sp., and an esthonioporate Esthoniopora clara Koromyslova, are described from Dapingian deposits of an unusual clayey-calcareous Hecker-type mudmound on the right bank of the Volkhov River in Leningrad Oblast ’ , north-western Russia. Combined X-ray microtomography, scanning electron microscopy, and light microscopy of thin sections were used to characterize their morphology. Analysis of the stratigraphic distribution of early cystoporate bryozoans suggests that Planopora n. gen. is the oldest с ystoporate bryozoan with an erect, bifoliate colony. The growth modes of these bryozoans are discussed. The colonies of P. volkhovensis n. gen. n. sp. and E. clara have an attachment structure, a holdfast, at their base, probably indicating their attachment to sponge spicules. The bryozoan H. insolitum n. sp. produced rod-like colonies, formed by overgrowing the problematic tubular fossil Sphenothallus Hall. It can be assumed that sponges with unfused siliceous spicules and individuals of Sphenothallus were numerous on the surface of the mudmound during its formation and provided a suitable substrate for settlement of bryozoan larvae.
Translated title of the contributionДревнейшие бифолиатные цистопораты и два других таксона мшанок из дапина (средний ордовик) северо-западной России)
Original languageEnglish
Pages (from-to)1-16
Number of pages16
JournalJournal of Paleontology
Early online date25 Sep 2020
DOIs
Publication statusPublished - 25 Sep 2020

Scopus subject areas

  • Earth and Planetary Sciences(all)

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