摘要
喙壳纲(Rostroconchia)是Pojeta,Runnegar,Morris和Newell于1972年正式建立的软体动物门的一个纲。根据已有的材料,它们只生存于古生代的海洋中,从早寒武世出现,至晚二叠世绝灭,至今尚未有关于三叠纪喙壳类的确切报道。对现今被归于这个纲的化石的描记,至少已经有150年以上的历史。但是由于对这类化石的特征认识不足,长期以来其分类位置没有被确定。许多研究者往往根据其一般形态,将个体小、时代较老的原始类型归于节肢动物,而将其较进化的类型作为双壳类化石进行研究,或者作为分类位置未定但具有特殊形态特征的软体动物来处理。
The fossil rostroconchs described and figured in the present paper were collected from the Tely-chian (Llandovery) strata in different localities of Guizhou, Shaanxi, and Anhui, South China. This fauna contains 2 genera and 7 species, including 4 new species and 3 unnamed species. The localities and strata together with the fossils contained therein are recognized as follows.
1. Upper Member of Xiushan Formation at Leijiatun, Shiqian County, Guizhou: Technophorus peregrinus sp. nov., T. Shiqianensis sp. nov., T. sp. 1, T. sp. 2.
2. Shenxuanyi Member of Ningqiang Formation at Yushitan, Ningqiang County, Shaanxi: Technophorus peregrinus sp. nov..
3. Yangpowan Member of Ningqiang Formation at Yushitan, Ningqiang County, Shaanxi: Pinnocaris lembods sp. nov..
4. Upper part of Wangjiawan Formation at Xiaoshizuizigou, Ningqiang County, Shaanxi: Pinnocaris lembodes sp. nov..
5. Wangjiawan Formation at Maopinggou, Ningqiang County, Shaanxi: Technophorus oblongus sp. nov..
6. Fengtou Formation at Xiazhucun, Chaoxian County, Anhui: Pinnocaris sp.
A range chart showing the known stratigraphic distributions of rostroconchs in South China with the graptolite zones as the standard is given in the Chinese text.
Rostroconchs are known only from Paleozoic or from earliest Cambrian to latest Permian. However, their greatest diversity at both family and generic levels occurs in the duration from the latest Cambrian (Fengshanian) to the earliest Ordovician, with only a few conocardioids existing during Silurian, such as the genera Bransonia Pojeta et Runnegar, and Hippocardia Brown (Pojeta and Runnegar, 1976; Runnegar, 1978). The early Silurian reberiid rostroconeh Technophorus minutus Zhang (1984) reported for the first time in China suggested their possible extension into the Silurian.
The genus Pinnocaris was reported from Iowa, Scotland, and Australia, and the genus Technophorus from North America, Central Europe, Siberia, Korea, Australia and probably South America. It is quite unusual that 8 species of reberiids occurred in the Telychian rocks of South China because no reberilds have been found from the strata younger than Ashgillian in the past records. Description of new species Pinnocaris lembodes sp. nov. (P1. Ⅰ, figs. 1—3)
Description Five specimens; small, strongly posteriorly elongated, with a length to height ratio of 3:1 or greater. Anterior end uniformly rounded; posterior dorsal margin gently concave; ventral margin arcuate in region of shell body, nearly straight along rostrum. Umbo projecting slightly above dorsal margin. Height of rostral posterior end and maximum height of shell in the ratio of about 1:5. Ornamentation consisting of fine comarginal growth lines. Pegma slightly oblique.
Comparison This species is somewhat similar to Pinnocaris lapworthi Etheridge (Pojeta and Runnegar, 1976, p. 54, p1. 9, figs. 13—23) from the Upper Ordovician Lower Ardmillan Series, Scotland, but differs from the latter in the concave dorsal margin, the smaller length to height ratio and the only slightly oblique pegma.
Horizon and locality Late Llandovery (Telychian); Upper part of Yangpowan Member of Ningqiang Formation, Yushitan, Ningqiang County, Shaanxi; Upper part of Wangjiawan Formation, Xiaoshizuizigou, Ningqiang County, Shaanxi.
Technophorus peregrinus sp. nov. (P1. Ⅰ, figs. 5—10)
Description Six well-preserved specimens; small, elongate, with length to height ratio of about 2:1. Anterior and ventral margins arcuate; dorsal margin gently concave while posterior margin with an obvious concavity. Posterior dorsal part elongated and compressed, drawn out into a rostrum. A single, long, and slightly curved radial rib extending from the umbo toward the postero-ventral angle, and intersecting the dorsal margin at an angle of 45°—50°. Surface ornamentation consisting of comarginal growth lines in anterior part of the shell body, with numerous radial ridges all over the middle part of the shell body and with rugose lines between the rib and posterior margin. An oblique pegma reflecting the only known internal feature.
Comparison This new species is characterized by the various surface ornamentation in different parts of the shell body and an oblique pegma. In general outline, this species is similar to Technophorus concellatus Ruedemann (Pojeta and Runnegar, 1976, p. 58, pl. 11, figs. 15—20) from the Middle Ordovician of New York, but the latter differs in the reticulate ornament over the shell body and the two posterior ribs.
Horizon and locality Late Llandovery (Telychian); Upper Member of Xiushan Formation, Leijiatnn, Shiqian County, Guizhou; Shenxuanyi Member of Ningqiang Formation, Yushitan. Ningqiang County, Shaanxi.
Technophorus shiqianensis sp. nov. (P1. Ⅱ, figs. 1—3)
Description Five specimens; small and elongate, with gently concave dorsal margin; anterior and ventral margins arcuate; posterior margin concave. Umbo projecting slightly above dorsal margin. Posterior dorsal part of the shell body elongated and compressed, drawn out into a rostrum; with a single slightly curved posterior rib from umbo to postero-ventral end. Ornament of comarginal growth lines and ridges, with a few weak radial lines in the middle part of the shell body. Pegma narrow and erect.
Comparison This species differs from Technophorus peregrinus sp. nov. in the comarginal or- nament over the shell body and the narrow and erect pegma.
Horizon and locality Late Llandovery (Telychian); Upper Member of Xiushan Formation, Leijiatun, Shiqian County, Guizhou.
Technophorus oblongus sp. nov. (P1. Ⅱ, figs. 4—7)
Description Six specimens; small and elongate, with nearly straight dorsal margin; anterior and antero-ventral margins arcuate; dorsal margin nearly parallel to the ventral margin; posterior margin straight; ratio of length to height about 2:1. A single and strong posterior rib extending from the umbo toward the posteroventral angle, and intersecting the dorsal margin at an angle of 30°—40°. Surface ornamentation consisting of fine and close comarginal growth lines. An oblique pegma indicating the only known internal feature.
Comparison This species is closely related to Technophorus monoplicatus Liu (Liu, 1979, p. 124, pl. 1, fig. 14) from the Middle Ordovician Jianling Formation of the Hainan Island in general outline and posterior radial rib, but differs from the latter in the oblique pegma and the length to height ratio.
Horizon and locality Late Llandovery (Telychian); Wangjiawan Formation, Maopinggou, Ningqiang County, Shaanxi.
出处
《古生物学报》
CAS
CSCD
北大核心
1990年第5期592-600,659-660,共9页
Acta Palaeontologica Sinica
基金
国家自然科学基金委员会4870090项目资助
为中英志留系研究项目的阶段成果之十三
