华南峡东地区最早的乳孔贝类腕足动物壳体超微结构和发育研究  

STUDIES ON THE SHELL ULTRASTRUCTURE AND ONTOGENY OF THE OLDEST ACROTRETID BRACHIOPODS FROM SOUTH CHINA

作　　者：张志亮[1,2] 张志飞 Lars Holmer[1,2] 

机构地区：[1]西北大学地质学系,大陆动力学国家重点实验室,陕西省早期生命与环境重点实验室,西安710069 [2]乌普萨拉大学地球科学系,瑞典乌普萨拉75236

出　　处：《古生物学报》2017年第4期483-503,共21页Acta Palaeontologica Sinica

基　　金：国家自然科学基金委员会杰出青年科学基金(41425008);国家自然科学基金委员会创新研究群体科学基金(41621003);国家自然科学基金重点国际合作项目(41720104002,41772002);高等学校学科创新引智计划(111项目,D17013)联合资助

摘　　要：乳孔贝(acrotretids)是一类繁盛于寒武纪晚期—奥陶纪并灭绝于泥盆纪的微型腕足动物,其特殊的壳体形态及柱状结构使其与其它舌形贝型腕足动物的系统学关系模糊不清。华南峡东地区寒武纪早期(第二世)水井沱组薄层灰岩中发现最早的精美保存的乳孔贝类腕足动物Eohadrotreta zhenbaensis(镇巴始壮贝)。本文首次解析Eohadrotreta的壳体形态和三级壳层结构。通过壳体显微结构的研究,解译出其个体存在的4个壳体发育阶段,即胎壳(protegulum)、幼年壳(brephic shell)、少年壳(neanic shell)和成年壳(mature shell),从而揭示乳孔贝悬浮滤食生活的幼虫阶段及其后的变态发育过程。更重要的是,在对这些壳体化石进行扫描成像过程中还发现精美保存的表皮细胞印模结构(epithelial cell moulds),它们在壳体内表面的分布规律反映了其与相应的软躯体附着区之间的紧密联系,揭示了其潜在的分类价值。随着对乳孔贝研究的深入,华南地区最早的乳孔贝类Eohadrotreta相继报道于扬子板块上的陕南、峡东、黔中地区,可能的华北板块南缘,以及喜马拉雅和澳大利亚南部地区,表明Eohadrotreta不仅是华南而且是不同大陆间寒武纪第二世洲际地层对比的重要化石。Acrotretids attained great diversity and cosmopolitan distributions in rocks of mid- Cambrian to Ordovician age, and went extinct by the end of the Devonian. However, bearing significantly special morphology and column structures, it has so far been difficult to analyze their phylogenetic relationship with other groups within the Class Lingulata. Eohadrotreta, one of the oldest known acrotretoid brachiopods, are described from the lower Cambrian Shuijingtuo Formation of South China. The ontogeny and three-layered shell structure are investigated for the first time. The detailed study of ultrastructure of shell indicates that there are four ontogenetic developmental stages of the acrotretid Eoha-drotreta, including protegulum, brephic shell, neanic shell, mature shell. The plank-totrophic larva and the metamorphosis are verified at least in Cambrian acrotretids. More importantly, exqui- sitely preserved epithelial cell moulds are identified on the whole interior of both ventral and dorsal valves. Investigation of the new material demonstrates that the disposition of epithelial cell moulds in shell interiors most likely is associated with regions of thickened muscle attachments a character that potentially could be of use in taxonomy. The cosmopolitan distribution of early Cambrian Eohadrotreta in southern Shaanxi, eastern Three Gorges area and central Guizhou of Yangtze Platform, possible North China, Himalaya and Australia demonstrates that can be a potential index fossil for the global stratigraphic correlation of Cambrian Series 2.

关 键 词：Eohadrotreta 乳孔贝 壳体结构 表皮细胞 印模 腕足动物 寒武纪早期 

分 类 号：Q915[天文地球—古生物学与地层学]