长江源区晚三叠世伟齿蛤科(双壳类)一新属--Quemocuomegalodon

记述青海唐古拉山北坡雀莫错附近晚三叠世甲丕拉组灰岩中的一类铰齿构造特殊的伟齿蛤类化石，建立新属Quemocuomegalodon gen．nov．及Q．orientus gen．et sp．nov．和Q．longitatus gen．et sp．nov.2新种，并简述伟齿蛤类的生活习性。

A NEW GENUS QUEMOCUOMEGALODON OF MEGALODONTIDAE FROM THE UPPER TRIASSIC IN THE SOURCE AREA OF THE YANGTZE RIVER, WESTERN CHINA

Very abundant and well preserved megalodontids have been found in the Jiapila Formation of the Upper Triassic from the area about 7km west of Quemocuo Lake, north slope of the Tanggula Mountains, Qinghai Province(Text fig.1). The Jiapila Formation disconformably overlies the Upper Permian Lapuchari Formation, and includes two members, the Upper and Lower members. The Lower Member consists of lime conglomerate, tuff, and pebbled tuff, intercalated with coarse grained quartzose sandstone, and pebbled coarse grained sandstone, 576m in thickness. No fossil has been found in the Lower Member yet. The Upper Member is made up of micrite, 97 160m thick, and yields 3 beds of megalodontids fossils (Text fig. 2). The large sized megalodontids (more than 80mm in height) occur in the lower part, while the small ones (less than 20mm in height) in the top. Those deposits indicate the shallow water,high energy and protected back barrier carbonate platform setting. The sedimentary environment of megalodont bearing rocks in northern Tibet is very similar to the Yaritaoshi limestone of Kyushu and the Hanagato limestone of Shikoku in the Sambosan belt of the southwest Japan. The megalodontids in studying area have very lower diversity in the levels of both genus and species. Except for a few specimens of Palaeocardita , megalodontids are associated with gastropods and algae. The new taxa of large sized megalodontids including Quemocuomegalodon Yao, Sba et Zhang (gen. nov.), Q. orientus Yao , Sba et Zhang (gen. et sp. nov.), and Q. longitatus Yao, Sba et Zhang (gen. et sp. nov.) are described in the present paper.