内蒙古宁城县道虎沟叶肢介化石群的时代

内蒙古赤峰宁城县道虎沟含丰富的叶肢介壳瓣及许多珍罕的软体化石 ,计有 1属 4种 :Euestheria ziliu-jingensis Chen,Euestheria haifanggouensis Chen,Euestheria jingyuanensis Chen,Euestheria luanpingensis Shen etNiu。这些分子都是我国中侏罗世早期自流井真叶肢介 (Euestheria ziliujingensis)动物群的重要成员 ,以个体较小、壳瓣圆或椭圆形、生长带具小网状装饰、种类单调、密集群生为特点 ,主要出现于中侏罗世早中期 (Bajocian- MiddleBothonia)。特别是 Euestheria luanpingensis Shen et Niu及其软体化石在道虎沟的发现 ,证明其层位应与冀北滦平九龙山组相当。道虎沟叶肢介群与中侏罗世晚期的假线叶肢介 (Pseudograpta)动物群的面貌相差甚远 ,与比其层位更高的大北沟组的尼斯脱叶肢介 (N estoria)动物群及义县组的东方叶肢介 (Eosestheria)动物群迥然不同 .

AGE OF THE FOSSIL CONCHOSTRACANS FROM DAOHUGOU OF NINGCHENG,INNER MONGOLIA

Daohugou village in Ningcheng, Inner Mongolia, is famous for yielding a variety of fossil groups, especially abundant conchostracans, which are very well preserved with soft parts and larval-stage individuals. The conchostracans are characterized by small carapaces, circleular or elliptical shapes, small reticulate ornamentation, including four species in one genus: E. ziliujingensis Chen, E. haifanggouensis Chen, E. jingyuanensis Chen, and Euestheria luanpingensis Shen et Niu. In China there are two conchostracan faunas of Middle Jurassic age, Euestheria ziliujingensis fauna in the lower part (Bajocian—middle Bathonian) and Pseudograpta fauna in the upper part (late Bathonian—Callovian). Euestheria ziliujingensis, E. haifanggouensis, and E. jingyuanensis found in Daohugou village are the important elements of the early Middle Jurassic Euestheria ziliujingensis fauna. Euestheria luanpingensis was known from the lower Middle Jurassic Jiulongshan Formation in northern Hebei where this species is also preserved with soft parts and larval-stage individuals. So the conchostracan assemblage from Daohugou should belong to the early Middle Jurassic Euestheria ziliujingensis fauna and are correlative with that in the Jiulongshan Formation. It is distinguished from the late Middle Jurassic Pseudograpta fauna by that the latter possesses mo- derate carapace, complex sculpture of the valve and diverse genera. It is quite different from the Upper Jurassic Nestoria fauna of the Dabeigou Formation and the famous Eosestheria fauna from the Yixian Formation, western Liaoning.