BILLENGSELLIDE AND ORTHIDE BRACHIOPODS: NEW INSIGHTS INTO EARLIEST ORDOVICIAN EVOLUTION AND BIOGEOGRAPHY FROM NORTHERN IRAN

Abstract:  The eastern Alborz Mountains of Iran comprise a significant peri-Gondwanan terrane relevant to the early evolution of late Cambrian – early Ordovician brachiopods incorporated into the emerging benthic biota of the Paleozoic Evolutionary Fauna. A low diversity brachiopod assemblage from the late Tremadocian unit of the Lashkarak Formation contains six new species including the polytoechioideans Polytoechia and Protambonites and the orthoideans Paralenorthis, Ranorthis, Tarfaya and Xianorthis . The fauna preserves the earliest records of Polytoechia , unknown previously outside Laurentia and the Uralian margin of Baltica, and of Paralenorthis and Ranorthis , which were widespread along Gondwanan margins and in Baltica from the Floian (Arenig), plus Xianorthis , known hitherto only from the Floian of South China. The enigmatic Tarfaya has an impunctate shell fabric and setigerous perforations along the posterior margin, indicating placement within the Orthoidea in a new Family Tarfayidae. New species of Polytoechia , Protambonites , Paralenorthis, Ranorthis , Tarfaya , Xianorthis are described.