Olenekian (Early Triassic) bivalves from the Salt Range and Surghar Range, Pakistan

摘要

Based on newly collected material from the uppermost Smithian and lower to middle Spathian (Olenekian, Lower Triassic) of the Salt Range and Surghar Range (Pakistan), 15 bivalve species belonging to 11 genera are described, including two new genera, Eobuchia and Dimorphoconcha, and one new species, Palaeoneilo? fortistriata. Eobuchia gen. nov. is placed in a new subfamily, the Eobuchiinae, which differs from the Buchiinae in having an almost planar and only moderately inclined or offset right anterior auricle. Inclination of the right anterior auricle is proposed as a synapomorphy of the revised suborder Monotidina, which includes the Buchiidae, Monotidae, Oxytomidae and, tentatively, the Dolponellidae. The Pseudomonotidae, Chaenocardiidae and Claraiidae are discussed as candidate ancestors of the Monotidina. Dimorphoconcha gen. nov., provisionally placed in the Limidae, is a morphologically unusual genus characterized by a globose shell centre and a strongly plicate fringe. Permophorus costatus, which was previously known exclusively from Permian strata, is reported from the Spathian of the Surghar Range. This record extends the range of P. costatus for at least 8Myr and makes it the first reported Lazarus species, with an outage of more than 2Myr after the end-Permian mass extinction. Ten of 15 species recognized in this study have not been reported from other regions, which may indicate increasing provincialism towards the end of the Early Triassic, or, alternatively, reflect the still insufficient knowledge of benthic faunas from the epoch that followed the greatest crisis in the history of life.