新类型的腕足动物——Guangdongina及其生态环境

A NEW TYPE OF BRACHIOPODS——GUANGDONGINA AND ITS ECOLOGICAL ENVIRONMENT

1980年,笔者在广州市西北郊嘉禾地区进行野外工作时,在下二叠统首次发现了一些形状特殊的化石标本,随后经多次采集,共获得标本17块。由于此类化石外形特殊,呈双豆荚状,壳上密布小孔,当时拟是一类新的化石,但究竟属何门类难以确定。后经详细观察、研究,确认此类标本应属一类新型的腕足动物。何锡麟、朱梅丽(1979)曾首次对类似标本进行过报道,认为是目前世界上尚未报道过的一种新类型。当前的标本与他们所报道的材料同属一大类,但其间仍有些重要差别。根据其主要特征,本文建立一新属Guangdongina。

A special type of brachiopods has been found from the upper part of the Lower Permian in Jiahe area of Guangzhou, which shows a symmetric and double bean-pod-shaped outline. They should be in the same group as those reported by He Xilin and Zhu Mei-li (1979), belonging to the family Permianellidae. But according to their main characters and in comparison with other types of brachiopods, it is relatively reasonable to place this type of fossils in Terebratullida and not to establish a new order as He and Zhu did. Based on the present specimens with special characters, a new genus——Guangdongina has been built in this paper, in which three new species and one undefined species are included. The well-preserved specimens make it possible to discuss their ecological environment during their lifetime. It is thought that Guangdongina lived by fixing their body on the crinoidal stem with the assistance of the pedicle and the sulcus and fold-bearing shell to support the body so as to lie on the substrate with the brachial valve. They got the organic suspending matter in water for food. Preserved together with them are mainly the benthonic faunas. So it comes to the conclusion that this new type of brachiopods lived in the neritic environment with sufficient sunlight, normal saltiness and abundant food. Description of new genus and species Order Terebratulida Moore, 1952 Superfamily Permianellacea He et Zhu,1979 Family Permianellidae He et Zhu, 1979 emend nov. Type genus: Permianella He et Zhu, 1979 Diagnosis: Shell small to medium-sized, double bean-pod-shaped in outline, concavoconvex or plano-convex, with pseudopunctate pores more or less separated at the anterior and connected as a whole at the posterior; pedical valve with sulcus, while brachial valve with fold; surface of shell smooth or only with some slightly concentric lines. Genus Guangdongina gen. nov. Type species: Guangdongina xiamaoensis gen et sp. nov. Diagnosis: Shell double bean-pod-shaped in outline, concavo-convex or piano-convex, a little separated at the anterior, with pseudopunctation; hing-line incurved; ventral palintrope well-developed; pedical beak incurved and protruding; foramen at apex; pedical valve with sulcus stretching from beak to the anterior; a broad ridge in sulcus; brachial valve with low fold; internal characters unknown. Comparison: This new genus and Permianella He et Zhu are much alike in outline, but the former differs from the latter in the shell slightly separated at the anterior, the sulcus stretching from beak to the anterior, the presence of a ridge in sulcus, the incurred hing-line well-developed, the ventral palintrope and the absence of two ears. Distribution: Upper part of Lower Permian; Jiahe, Guangzhou, Guangdong. Guangdongina xiamaoensis gen. et sp. nov. (P1. Ⅰ, figs. 1—9; p1. Ⅱ, figs. 1—7) Deseription: Shell medium-sized, about 18— 30 mm in length, and 15—20 mm in width (near the anterior), double bean-pod-shaped in outline, concavo-convex, being separated into two parts at the anterior; hing-line short and incurved; ventral beak sharp, conspicuous, with relatively broad palintrope; pedical foramen at apex; visceral cavity narrow; pedical valve with a strong convexity at the posterior but tending to be flattened at the anterior; sulcus stretching from beak to the anterior, narrow furrow-shaped at the posterior but getting broader at the middle and anterior; bottom of sulcus deep and round, with a broad ridge in sulcus; two pairs of elongate ridge-like adductor scars present laterally in the inner part of pedicai valve. Brachial valve slightly concave, with low and flattened fold. Two layers of shell with the outer one rather thin and dense, and the inner one displaying scattered tubercles or pseudopuncta; surface of shell smooth or with some gently concerntic lines. Horizon and locality: Upper part of Douling Formation, Jiahe, Guangzhou, Guangdong. Guangdongina leguminiformis gen. et sp. nov. (P1. Ⅲ, figs. 4—8) Shell moderate-sized, 35mm in length, and 22 mm in width (at the middle part); appearing narrow at the posterior but getting wider at the middle, and then becoming narrow again, typical double bean-pod-shaped, separated only a little at the anterior, concavo-convex or almost piano-convex; beak incurved; umbo convex; pedical valve strongly convex, with sulcus arising from beak and reaching the anterior; brachial valve slightly concave or plain; bottom of sulcus plain, with a ridge stretching along sulcus; two pairs of ridge-like adductor scars present laterally. Texture of shell divided into two layers, with many pseudopunctate pores in the inner one. Comparison: This species is similar to Guangdongina xiamaoensis in outline, but it is easily distinguished from the latter by its relatively large shell with the greatest width at the middle part, and its form of sulcus without much variation. Horizon and locality: Same as the preceding species. Guangdongina perforans gen. et sp. nov. (P1, Ⅱ, fig, 8; p1. Ⅲ, figs. 1—3) Description: Shell small to medium-sized, about 24 mm in length, and 20 mm in width, broad double bean-pod-shaped in outline, concavo-convex, connected at the middle and posteriorbut separated at the anterior; hing-line incurved; palintrope developed; brachial valve gently concave; pedical valve strongly convex with sulcus, which is broad furrow-shaped and extending almost from beak to the anterior; bottom of sulcus plain; lateral walls erect; a broad ridge present; in sulcus with many tubercles. Outer layer of shell mostly preserved at the margin of valve, with smooth plication or some slight growth-lines; inner layer with many tubercles and pseudopuncta observed on the surface. Comparison: This species differs from the preceding two species in the broader posterior part, the sulcus maintaining broad furrow-shaped from beak to the anterior, the plain bottom of sulcus and the larger pseudopunctate pores. Horizon and locality: Same as the preceding species. Guangdongina sp. (P1. Ⅱ, fig. 9) Deseription: Shell in small size, preserved with part of the specimen which is 10 mm in length, about 13 mm in estimated length and 12 mm in width, concavo-convex, divided into two parts by sulcus and double bean-pod-shaped in outline; pedical valve with sulcus stretching to 1/3 from beak but not reaching it; bottom of sulcus deep and round; a ridge in sulcus with some scattered tubercles on it. Outer layer of shell thin, with gentle growthlines on surface; inner layer with densely scatte red pseudopuncta, which are small and irregularly. Comparison: The specimen is incompletely preserved, but it can be distinguished by its much smaller shell, sulcus not stretching to beak, small and irregularly ranging pseudopunctate pores. Horizon and locality: Same as the preceding species.