陕西南部最古老的放射虫化石

用酸蚀法从陕西镇巴县小洋剖面下寒武统水井沱组分离出大量保存精美的双瓣壳格子状化石,经电子探针进行成分分析和扫描电镜下进行形态学研究,确认为迄今已知最古老的放射虫化石。这些最早出现的放射虫不同于泡沫虫类,而出入意外地是一类褐色虫(Phaeodoria)。基于这些材料,建立了1个新科(Eoconchariidae)、3个新属(Eoconcharium、Fusuconohnrium和Quadratapora)和7个新种。

THE OLDEST KNOWN WELL-PRESERVED PHAEODARIA (RADIOLARIA) FROM SOUTHERN SHAANXI

Many well-preserved radiolarians etched from limestones of the Shui-jingtuo Formation( Lower part of lover Cambrian) of Zhenba County, Shaan xi Province are reported in this paper. The microprobc readings obtained from radiolarian shells show that they are mainly composed of silicon dioxide? however, they are morphologically similar to the Conchariidae (belonging to the Order Phaeodaria) whose shells are poorly silicified and hardly fossilized. These oldest known radiolarians probably lived as benthos and not like their extant descendants which are planktonic. All the specimens collected from eleven different layers of the Shuijingtuo Formation are grouped into a new family, three ne\v genera and seven ncu species, which are briefly described below. Eoconchariidae fam. nov.. Phaeodaria with a bivalved lattice-shell, composed of two free opposite valvesj the chemical composition is mainly of opaline silica with sonic calcium phosphate. Eoconcharium gen. nov.. Valves are made of bars and pores encircled by barsi the pores in the central area of valves are larger, becoming smaller towards margins; there are spines at the intersections of bars; both dorsal and ventral valves have margins which fit one into the other. E,chinense gen. et sp. nov. (p1. I , figs.1 ?13): Truncated-oval-shaped in dorsal or ventral view, with hat - like spines. E.ovalum gen.et sp. nov. (pl.II,figs. 1 -16): Oval - shaped in dorsal or ventral view. E.rhomboidale gen.et sp. nov.(p1.III, figs.5-12): Subrhombic or elongate oval with both ends pointed in dorsal or ventral view. E .spiniferum gen. et sp. nov. (p1. III figs. 1-4): It differs from all other species of genus Eoconcharium in that its spines are not hat-like but taperj and the pores are somewhat uniform. Fusuconcharium gen. nov.: Fusiform or elongate oval in dorsal or ventral view; thare are nodules on the valves but no spines. F.typicum gen. et sp. nov, (pi. IV , figs. 1-2): Fusiform in dorsal or ventral view; nodules are irregularly arranged on the bars larger and smaller pores are in random distribution. F.minimum gen. et sp. nov. (pl.TV,fig.3): elongate oval in dorsal view; nodules occur in clusters on disc-like swellings; pores are larger in certral area of the valve, becoming smaller towards the margins. Quadratapora gen. nov.. Pores are equal and rectangular; there are disc-like swellings at the intersections of bars; the valve margins are not smooth. Q.zhenbaensis gen. et sp. nov. (p1.IV, fig. 4): Diagnosis is the same as that of genus Quadratapora,