摘要
一、前言皖南中奥陶世胡乐组为黑色笔石页岩,所含笔石化石自下而上可分为3个笔石带:(1)Glyptograptus teretiusculus带;(2)Nemagraptus gracilis带;(3)Dicranograptus sinensis带。作为叉笔石动物群的重要组成分子,双头笔石开始出现于第1带,并于第2带和第3带获得了迅速分异和发展。皖南胡乐组双头笔石的研究始于本世纪30年代。许杰(1934)
The Middle Ordovician Hulo Formation in southern Anhui is made up of graptolite-bearmg black shales, in which the graptolite assemblages belong to the Dicellograptus fauna. As an important constituent member of this fauna, Dicranograptus makes its first appearance in the Glyptograptus teretiusculus zone, and then diverges and develops in the Nemagraptus gracilis and Dicranograptus sinensis zones. Based on biostratigraphical data from the Xiakengwu stratigraphic section in the Hulo district, and applying the method of numerical cladistics, the present authors have made a preliminary probe into the evolution of Dicranograptus in the Hulo Formation. As a resuit, the evolutionary pattern (Text-figs. 4, 5) shows that all the graptolite species under study originated from a common hypothetic taxonomic unit (HTU_1) and then evolved in two lineages as listed below:
Ⅰ_1. HTU_1→Dicellograptus smithi→Dicellograptus intortus→Dicranograptus furcatus;
Ⅰ_2 HTU_2→Dicranograptus yangtzensis→other dicranograptids, from which two evolutionary branches have evolved:
Ⅱ_1. Dicranograptus yangtzensis→Dicranograptus cyathiformis→Dicranograptus ramosus;
Ⅱ_2. Dicranograptus yangtzensis→a hypothetic taxonomic unit (HTU_2), from which two subbranches have evolved;
Ⅲ_1. HTU_2→Dicranograptus kansuensis→Dicranograptus diapason;
Ⅲ_2 HTU_2→another hypothetic taxonomic unit (HTU_3)→Dicranograptus sinensis and Dicranograptus ziczac minutus.
出处
《古生物学报》
CAS
CSCD
北大核心
1991年第3期377-387,431,共11页
Acta Palaeontologica Sinica
基金
高等学校博士学科点专项科研技术基金
