Silurian (Aeronian) rhynchonelliform brachiopods of Shabdjereh, south-west Central Iran and their significance for early spiriferide evolution

摘要

The Silurian (Aeronian) post-extinction recovery brachiopod fauna of Iran and Afghanistan is characterized by a proliferation of the Stegocornu Brachiopod Association, which includes prominent endemic rhynchonellide and spiriferide components. A local variety of that association, recently recovered from the Shabdjereh Formation of Kerman Province, East-Central Iran, contains eight brachiopod species, including the rhynchonellide Kermanirhyncha granulata gen. et sp. nov., and the spiriferides Levanispirifer alatus gen. et sp. nov. and Mictospirifer obtusus sp. nov. A new phylogenetic analysis of the earliest Late Ordovician to Aeronian spiriferides, within the general context of the Ordovician radiation of rhynchonelliform brachiopods with calcified brachial supports, reveals the following two major centres of biodiversification and dispersal: (1) the Laurentian palaeocontinent, which is the likely place of origin and initial diversification of the atrypide suborders Lissatrypidina and Anazygidina; and (2) the assemblage of Kazakh island arcs and microplates (known also as Kazakh Archipelago), which was the centre of origin and initial dispersal of the atrypid suborder Atrypidina and the order Spiriferida. South China represents a major refuge, where spiriferides survived the terminal Ordovician extinction and from where they dispersed towards adjacent parts of Gondwana including the Iranian terranes. The latter areas were an important secondary centre of spiriferide biodiversification during the Aeronian Age.