盘县动物群研究进展

盘县动物群是以保存完整、精美、属种丰富的海生爬行动物化石为特色,伴生海生无脊椎动物化石的一套完整的珍稀古生物群落.盘县动物群产于中三叠统关岭组上段,属于牙形石Nicoraella kockeli带,时代为中三叠世安尼期的Pelsonian亚期,早于著名的意大利-瑞士交界处Monte San Giorgio地区的Grenzbitumenzone动物群(安尼阶-拉丁阶界线附近),是目前世界上中三叠世最老的海生爬行类动物群.它的发现和研究填补了海生爬行动物演化的早期链条,增强了人们对海生爬行动物各类群的起源、演化、系统发育、古生物地理以及动物群特异埋藏理论的认识.近期研究表明,盘县动物群中的海生爬行动物: (1) 具有较高的分异度,已报道5属5种,拥有了目前发现的最古老的混鱼龙科分子、鸥龙属分子、较老的幻龙属分子和真正适应水生生活的原龙类以及诸多未描述的类群;(2) 动物群多由适应近岸浅水环境的类群组成,在面貌上呈现出强烈的西特提斯生物亲近性;(3) 动物群属特异埋藏,赋存层分布有4～5层凝灰岩,化学特征分析显示存在7次火山间歇性喷发活动,火山活动导致的生态环境急剧恶化可能是动物群集群绝灭的直接诱因.

Advance in Studies of the Panxian Fauna

The Panxian Fauna is mainly characterized by well-preserved and articulated skeletons of Middle Triassic (Anisian) marine reptiles with high diversity,associated with abundant invertebrate fossils,such as bivalves,brachiopods as well as cephalopods,and some as yet undescribed taxa. Stratigraphically,it is occurred at the Upper Member of the Guanling Formation,ascribed to the conodont Nicoraella kockeli Zone,which indicates that the age of this fauna is Pelsonian (Middle Anisian). Therefore,the Panxian Fauna is older than the Grenzbitumenzone fauna at Besano/Monte San Giorgio area of Italy/Switzerland border (near Anisian/Ladinian boundary),and represents the oldest marine reptile fauna of the Middle Triassic throughout the world. Such a rich,diversified and perfectly preserved paleontological assemblage with the exact stratigraphic horizon and definitive age not only provides abundant materials for exploring the taxonomy,evolution,and origin of the marine reptiles,but also has great significance for developing the study of paleoecology and biogeographic provincialism. So far,five genus and five species,including the oldest mixosaurid ichthyosaurs,the oldest lariosaurs and the first true aquatic protorosaur(Dinocephalosaurus orientalis),have been reported from the Panxian Fauna. Most of them are adapted to epicontinental environment or shallow sea,and show a strong West Tethyan affinity. The strata bearing the Panxian fauna consists of four or five tuff beds and seven volcanicities were recognized,which might be caused the extinction of these marine reptile animals directly.