论二叠贝类(Permianellids)

ON PERMIANELLIDS (BRACHIOPODA)

本文研究了二叠纪一类形态很特殊的腕足动物——二叠贝类。在仔细观察了迄今所有的有关材料和采用系统切面法和电镜扫描技术分析部分标本后,认为二叠贝类代表着欧姆贝目的1个新支系,即二叠贝科,包括3属,其中1新属(Laterispina gen. nov. )和1新种(Laterispina liaoi gen. et sp. nov. )。根据二叠贝类在地层分布上所显示的形态变化,将二叠贝类的形态演化分成3个阶段:早二叠世、晚二叠世早期和晚二叠世晚期。本文还探讨了二叠贝类的生态特点,认为它属近礁相生物群落中或浅海近浪基面泥质基底上生物群落中的高层附生悬食类,是二叠纪特提斯生物群的特有类群。

The permianellids are so peculiar in morphology that considerable confusion about their systematic position remains to be clarified. They were first described by Termier et al. in 1974 and assigned to the oldhaminids. After then, several authors introduced some genera based on their own permianellid specimens, namely, Permianella He et Zhu, 1979, Dipunctella Liang, 1982, Guangjiayanella Yang, 1984, and Guangdongina Mu et Liu 1989, and referred them to different orders of the Articulate Brachiopoda, such as Productidina and Terebratulida. Some authors even proposed a new order for them. A detailed study of the shell-shape, ornament, internal morphology and shell structure shows that the permianellids are characterized by their concavo-convex profile, bilobate outline, outer surface decorated with dense, tiny tubercles, long narrow brachial ridge on each lobe of dorsal valve and hollow middle muscle attachment platform on ventral valve. Their shell displays a two-layered structure, with the outer layer composed of tubercle core, pseudopuncta and laminar fibre and the inner layer of pseudopuncta and laminar fibre. All these characters indicate that the permianellids have an affinity to the oldhaminids and might be treated as a new family of this order. The permianellids have been found in Afghanistan, Thailand, Japan and China, forming an endemic group of the Permian Tethyan fauna. Phylogenetically, they can be divided into three stages represented by three genera respectively, namely, Dicystoconcha Termier et al., 1974 of the Early Permian (which is a valid name with other genera Dipunctella Liang (part), Guangiiayanella Yang and Guangdongina Mu et Liu as its later synonyms), Permianella He et Zhu of the early Late Permian and Laterispina gen. nov. of the latest Permian. The latter two genera, which are mainly different in lateral margins, can be distinguished from the former by their more elongate outline, deeper incision and more complicated lateral margins. It is interesting to note that the permianellids appeared in a high diversity stage of the oldhaminids as those groups with bilobate outline did in a similar stage of orders of the Articulate Brachiopoda except Rhynchonellida and Spiriferida. Based on analysis of attachment pattern, characters of population, lithological facies and associated faunas, it is inferred that the permianellids belong to higher epizoan suspension feeders in the community of near-reef or of mud-bottom near wave base. Description of Family and Genus Suborder Oldhaminidina Williams, 1953 Superfamily Lyttoniacea Waagen, 1883 Family Permianellidae He et Zhu, 1979 Shell concavo-convex, bilobate in outline, with sulcus in ventral valve, fold in dorsal valve and emarginate anterior margin, ornamented with dense, tiny tubercles; ventral valve with teeth and middle muscle attachment platform; dorsal valve with cardinal process and socket, simple bracbial ridge developed; shell substance mainly pseudopunctate. Genera: Dicystoconcha Termier et al., 1974; Perrnianella He et Zhu, 1979; Laterispina gen. nov.. Occurrence: Lower Permian (Chihsian) to Upper Permian (Changhsingian), Afghanistan, China, Japan and Thailand. Genus Laterispina gen. nov. Type species: Laterispina liaoi gen. et sp. nov., pl. Ⅱ, figs. 4—12. Distinguishing characters: Permianellidae with large shell, short sulcus and fold, beltlike or triangular in outline; anterior incision much deeper; margins ornamented with marginal spines like railings. Species assigned to this genus: Laterispina liaoi gen. et sp. nov.. Remarks: This genus is distinguished from Dicystoconcha Termier et al., 1974 and Permianella He et Zhu, 1979 by its much deeper incision and marginal spines. Occurrence: Changhsingian, Guangxi, Sichuan and Guizhou, China.