Permian gastropods from the Ratburi Limestone, Khao Phrik, Central Thailand

Abstract

A new silicified Middle Permian gastropod fauna is reported from Central Thailand. It is the first diverse Permian gastropod assemblage described from the Sibumasu terrane. The gastropod fauna comes from fore-reef shallow water carbonates of the Middle Permian (Wordian) limestones of the Ratburi Group exposed at Khao Phrik, Ratchaburi Province. Thirty-four gastropod species are reported, 17 nominate species and 17 in open nomenclature. Nine species are new to science: Retispira khaophrikensis, Amaurotoma? multispirata, Eoplatyzona ratchaburiensis, Hesperiella cyrtocostata, Worthenia? waterhousei, Stegocoelia centrosinuata, Procerithium? inaequetuberculata, Chlorozyga asiatica and Hyphantozyga? khaophrikensis. The gastropod assemblage is strongly dominated by bellerophontids (especially Warthia and Retispira). The fauna shares only a few species with faunas from other Permian deposits in Thailand and elsewhere, namely the previously described gastropod fauna of the Tak Fa Limestone. The fauna shows relationships to Late Palaeozoic gastropod faunas from the Palaeo-Tethys, such as those of Australia and Malaysia.