Ecological and Taxonomical Succession of Rhynchonellids (Brachiopoda) in the Devonian and Early Carboniferous of Transcaucasia

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.