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新发现的双壳类化石命名为Baxoitrigonia baxoiensis gen.et sp.nov.,产地为藏东八宿林卡家东,化石产于景星动物群之下的拉贡塘组下段,同层位有菊石和其他海相双壳类,时代为晚侏罗世Tithonian期;化石的外部特征很接近于三角蛤类Iotrigonia属,但前闭肌痕特征又相似于类三角蚌类,被认为是三角蛤类闯入非海相领域后演变成类三角蚌类的产物.此发现提供了生物和地层两方面的直接证据,证明非海相类三角蚌类(Trigonioidoidea超科)起源于海相三角蛤类(Trigoniida目),而不是起源于珠蚌类(Unionida目).海相三角蛤类闯入边缘隔绝的洛隆—八宿地区并演变为非海相类三角蚌类,是一次典型的边域成种事件.“,”The new trigoniid taxon Baxoitrigonia baxoiensis gen.et sp.nov.of Tithonian (Late Jurassic) age is reported from the Baxoi (Basu) area in eastern Tibet,China.The external characters of this new taxon are fairly similar to those of the genus Iotrigonia,but it is characterized by a distinct median groove,and the anterior adductor muscle scar is similar to that of the Trigonioidoidea.This observation provides more direct evidence that the non-marine Trigonioidoidea (order Trigoniida) were derived from marine Trigoniida and not from the Unionoidea (order Unionida).This derivation correlates with the biostratigraphical sequence in eastern Tibet;Baxoitrigonia baxoiensis directly preceded the Jingxing fauna that comprises primal Trigonioidoidea that lived in non-marine environments.The invasion of the marine trigoniid ancestors of the Trigonioidoidea into non-marine environments,which took place in the peripherally isolated Lhorong-Baxoi region,and their evolution into non-marine Trigonioidoidea is a typical example of peripatric speciation.