内蒙古乌海市以南约２５ｋｍ的桌子山地区中奥陶世（ｅａｒｌｙｌａｔｅＡｒｅｎｉｇ）三道坎组底部产一种原始的扭月贝类腕足动物，经笔者鉴定，为中华西方贝（新种）（Ｈｅｓｐｅｒｉｎｉａｓｉｎｅｎｓｉｓｓｐ．ｎｏｖ．），系统切片研究证实其为迄今所知最古老的一种扭月贝类，其双叶型主突起略突伸于铰合缘的后方、低而较弱的铰窝脊向侧后方延伸靠近铰合缘等特征都表明该种属于扭月贝科（Ｓｔｒｏｐｈｏｍｅｎｉｄａｅ）。实现从褶脊贝类向扭月贝类的演化需要在背壳内部建立这样一些形态上的演化新质：双叶型主突起，一对朝后侧方略弯曲的铰窝脊，横肌脊，以及侧隔板，所有这些构造特征，Ｈｅｓｐｅｒｉｎｉａｓｉｎｅｎｓｉｓｓｐ．ｎｏｖ．均已具备，因此，这表明了扭月贝类与褶脊贝类的分化要早于晚Ａｒｅｎｉｇ。除Ｈ．ｓｉｎｅｎｓｉｓ外，世界其它地区也有早期扭月贝类的报道，但多产于Ｌｌａｎｖｉｒｎ或更新的一些地层中，如发现于挪威Ｗｈｉｔｅｒｏｃｋ组的ＴｒｏｔｌａｎｄｅｌａｌｏｋｉＮｅｕｍａｎ（ＮｅｕｍａｎａｎｄＢｒｕｔｏｎ，１９７４），英国威尔士中部Ｌｌａｎｖｉｒｎ地层中的Ｍｕｒｉｎｅｌａｓｐ．，‘Ｍａｃｒｏｃｏｅｌｉａ’ｌａｎｄｅｉｌｏｅｎｓｉｓｅｌｏｎ

New material from the basal Sandaokan Formation (early late Arenig,Ordovician) of southern Inner Mongolia,North China represents a new species, Hesperinia sinensis, which is the oldest known strophomenoid brachiopods.It extends the record of this group into the Arenig,earlier than Llanvirn as generally known in the literature.Its cardinalia and some other crucial characters indicate that it is a strophomenid.The most important morphological transformations characterising the divergence of strophomenoids from ancestral plectambonitoids were the development of: a bilobed cardinal process, a pair of postero laterally curved socket ridges, and transmuscle ridges and side septa in the dorsal valve.These innovations are present in H.sinensis sp.nov.and confirm that the divergence of the strophomenoids from the plectambonitoids was pre late Arenig in age.Synecological analysis shows that Hesperinia sinensis sp.nov.occupied a near shore,shallow water,relatively high energy environment.

Q915.642