Early jurassic shallow-marine bivalves from Xiaping, southern Hunan, China

From shallow-marine siliciclastic deposits of the Xintianmen Formation (Early Jurassic, late Hettangian? to early Sinemurian) near Xiaping, south-eastern Hunan Province, central southern China, four small bivalve-dominated fossil assemblages are described which distinctly differ from each other taxonomically. The taphonomic features of the two assemblages from the lower Xintianmen Formation indicate deposition under fairly calm conditions, whereas those of the two assemblages from the upper Xintianmen Formation indicate deposition under the influence of currents and during a storm event, respectively. The bivalves show taxonomic affinities to penecontemporaneous bivalve faunas of the Tethyan and the Circumpacific region, but the species are restricted to South China and adjacent areas. The new parallelodontids Cosmetodon xiapingensis n. sp. and Cosmetodon xintianmenensis n. sp. are of significance, because parallelodontids hitherto have only very rarely been mentioned from the Lower Jurassic of southern China. Further, the new species Pseudosaxicava huananensis n. sp., Pseudosaxicava palaeosinensis n. sp., Nicaniella grabaui n. sp., Protocardia moshuiwanensis n. sp., Tancredia nanlingensis n.sp. and Pleuromya xiangensis n.sp. are erected. The revision of earlier taxonomic assignments led especially in the case of pectinids and hiatellids to a reduction of the number of taxa known from the Lower Jurassic of southern China.