摘要
一、前言商县盆地呈北西-南东向延伸于陕西南部的商县和丹凤县境内,长约60km,宽约5km,为北秦岭中段一个小型中新生代构造盆地。晚期中生代和新生代红层在盆地中颇为发育。其中,晚期中生代地层主要出露于盆地西北部的熊耳山至商县县城附近及王山底一带,为河流、湖泊相砂砾岩、页岩,夹有油页岩和煤线,含有丰富的双壳类、介形类、叶肢介等淡水动物化石以及昆虫和少量植物化石。根据地层和生物群总体特征。
The Jehol fauna from the Shangxian Basin has been first reported in the Qinling Mountains. The fossils were collected from the middle part of Upper Jurassic Donghe Group, including 11 species of conchostracans and one insect, among which Eosestheria gouyuensis sp. nov., E. shaannanensis sp. nov. and Diestheria cuneata sp. nov. are new forms; E. shuchengenis Chen and E. cf. or bicularis Chen have been reported from the Maotanchang Formation of Shucheng, Anhui; while E. aff. middendorfii (Jones) and Ephemeropsis trisetalis Eichwald are the most common members of this fauna widely distributed in N. China, Mongolia and Transbaikalia. According to this study, it is reasonable to assign the Donghe Group to the Late Jurassic age.
Description of new species Eosestheria gouyuensis sp. nov.(P1.Ⅰ, figs. 1—4)
Description: Carapace valve large, longish-wedged to longish-elliptical in outline, 19—25mm in length and 10—12.5mm in height; dorsal margin long; umbo small, located near centre of dorsal margin. Anterior margin slightly arched; ventral margin broadly arcuate; posterior margin contracted to sharply round. Anterior height greater than posterior one. Growth bands 25 in number; upper growth bands of valve ornamented with reticulation, while lower ones with more regular radial ridges.
Comparison: This species is more similar to E. elongata (Kob. et Kuz.) in the outline of valve and the basic ornament, but differs in the umbo which is closer to the centre of the dorsal margin than the latter.
Eosestheria shaannanensis sp. nov.(P1. Ⅲ, figs. 1, 2)
Description: Carapace valve large in size, quadrate:elliptical in outline; holotype 21mm in length, 14mm in breadth. Dorsal margin short; umbo located near centre of dorsal margin. Anterior margin straighter; ventral margin broadly round; posterior margin round. Anterior height greater than posterior one. About 30 broad, flat and well- distributed growth bands observable (with about 10 of them closed near ventral margin). Growth bands in anterior and ventral regions of valve ornamented with more regular radial ridges; those in dorsal part with thin and delicate reticulation.
Comparison: This species is more similar to E. triformis Chen in outline of valve and seat of umbo on dorsal margin; but in the latter, the growth bands of valve are ornamented with large and small reticulate sculptures as well as radial ridges.
Diestheria cuneata sp. nov.(P1. Ⅱ, fig. 3)
Description: Carapace valve slightly convex, cuneate in outline; holotype 16mm in length, 8.3mm in height; 18 growth lines observable; growth bands broad and flat; anterior height greater than posterior one. Growth bands on upper part of valve ornamented with reticulate sculpture; but those on ventral part ornamented with radial ridges. Radial ridges in postero-ventral region delicate, close and ornamented with overlapped reticulation; those in antero-ventral region ornamented with clear reticulate inner ornament.
Comparison and Remarks: The cuneate form of the valve in this species is unique to the genus Diestheria. In the present specimen, the dent of growth lines in the middle ventral part of the valve is a scar resulting from injury.
出处
《古生物学报》
CAS
CSCD
北大核心
1990年第3期376-384,410-412,共9页
Acta Palaeontologica Sinica
