Ecological and Taxonomical Succession of Rhynchonellids (Brachiopoda) in the Devonian and Early Carboniferous of Transca
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ogical and Taxonomical Succession of Rhynchonellids (Brachiopoda) in the Devonian and Early Carboniferous of Transcaucasia A. V. Pakhnevich* Borissiak Paleontological Institute, Russian Academy of Sciences, Moscow, 117647 Russia *e-mail: [email protected] Received November 21, 2019; revised December 23, 2019; accepted December 26, 2019
Abstract—The Devonian and Early Carboniferous brachiopod assemblages of the order Rhynchonellida from Transcaucasia (Nakhchivan Autonomous Republic of Azerbaijan and Armenia) are described. The succession of dominating rhynchonellid superfamilies and ecological types has been identified. Rhynchonellids were numerous in the Devonian; in the Early and Middle Devonian, the representatives of the superfamily Uncinuloidea prevailed. Their relict species survived up to the beginning of Famennian. The free-lying and anchoring cavern-dwelling rhynchonellids dominated in the Early and Middle Devonian. This ecological subtype is recognized for the first time. The rhynchonellid taxonomic and ecological groups changed at the Frasnian–Famennian boundary but rhynchonellids remained a significant part of the brachiopod fauna. The variability of rhynchonellids decreased at the Famennian–Tournaisian boundary but the superfamily Rhynchotrematoidea and the rhynchonellid anchoring ecological type continued to dominate starting from the Frasnian. The role of Rhynchonellida in the Early Carboniferous brachiopod fauna is insignificant. The decrease of variability within some zones is probably connected with taphonomic conditions. Keywords: brachiopods, Rhynchonellida, Devonian, Lower Carboniferous, Transcaucasia DOI: 10.1134/S0031030120060064
INTRODUCTION The Lower Devonian–Lower Carboniferous sections of the Nakhchivan Autonomous Republic of Azerbaijan and nearby areas of Armenia are significant for faunology and stratigraphy. One of these sections on the slope of Geran-Kalasy Mountain is composed of continuous marine deposits and is one of the most complete Upper Devonian–Lower Carboniferous sections (Grechishnikova and Levitskii, 2011). The sections of Transcaucasia are rich in various fauna; the Devonian deposits contain foraminifers, stromatoporates, chaetetids, heliolitids, tabulates, rugose corals, gastropods, bivalves, cephalopods (including nautiloids), tentaculites, trilobites, ostracodes, bryozoans, conodonts, crinoids, fishes, and algae. The Carboniferous deposits contain foraminifers, tabulates, ostracodes, crinoids, conodonts, and algae. One of the most numerous groups both in the Devonian and Carboniferous deposits are the brachiopods. They dominated in the Devonian and Carboniferous seas, but the dominating orders were different. The rhynchonellids were found in the deposits of almost all zones (accepted after Grechishnikova, 2018). Mirieva (2010) published the first description of the rhynchonellid assemblages; however, the presence of some rhynchonellid species is controversial and other described assemblages are
incomplete. These assemblages were described in detail by Pakhnevich (2018). Th
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