EOPHILOBRYOIDELLA SINOANISICA NEW GENUS AND SPECIES, AN EARLY PHILOBRYID BIVALVE FROM THE UPPER ANISIAN (MIDDLE TRIASSIC) OF QINGYAN, SOUTHWESTERN CHINA

Abstract

The bivalves of early late Anisian (Middle Triassic) age from Leidapo (also Bangtoupo) in the northeastern vicinity of Qingyan in the south-central part of Guizhou Province, southwestern China (Fig. 1), are highly diverse and fairly well studied (e.g., Chen et al., 1974; Yin, 1974; Nanjing Institute of Geology and Palaeontology, 1976; Gan and Yin, 1978; also Stiller, 2001). The study of these Anisian fossil assemblages began with Koken (1900) and Hsu and Chen (1943). The renewed study of this site and its fossil assemblages by Stiller (1997, 2001) and Chen et al. (2001) yielded a bivalve taxon with unusual and, for an early Mesozoic species, unexpected hinge features. The new taxon is fairly common at Leidapo/Bangtoupo; nevertheless it was only recently recognized (Stiller, 2001) and has not heretofore been described. Figure 1 —Geographic location of Qingyan in Guizhou Province, southwestern China, and map of the northeastern vicinity of Qingyan with the hillock Leidapo/Bangtoupo The only bivalve group having comparable hinge features is the Philobryidae (Arcoida, Limopsoidea). This small bivalve family has only been described from Eocene and more recent rocks (Keen, 1969; Tevesz, 1977), but Skelton and Benton (1993, p. 246) mentioned a yet undescribed philobryid from the Kimmeridgian (Upper Jurassic) without giving any further information. The features of the new taxon from southwestern China, particularly those of the hinge region, strongly suggest an assignment to the Philobryidae. The finding of the new taxon described herein thus significantly extends the stratigraphic range of this family to the lower upper Anisian (lower Middle Triassic). The specimens are from the highly fossiliferous section at the hillock called Leidapo (or Bangtoupo) (Fig. 1), which comprises a succession of generally thinly bedded, more or less marly and mostly slightly silty mudstones with thin, more calcareous intercalations …