重庆侏罗系杨氏璧山上龙(一淡水蛇颈龙)的再研究(英文)

侏罗纪的蛇颈龙类化石主要发现于欧洲 ,在世界的其他地区则比较少见。亚洲的蛇颈龙化石 ,尤其是侏罗纪的属种大多破碎而难以鉴别 (Sato,1 998)。到目前为止 ,Bishanopliosaurusyoungi(Dong,1 980 )和Yuzhoupliosauruschengjiangensis(Zhang,1 985)是亚洲地区最为完整的侏罗纪蛇颈龙类化石 ,并且化石产自对于蛇颈龙而言比较罕见的淡水沉积 ,因此这些材料对于了解该类群的系统发育、历史动物地理和古生态来说非常重要。本文重新详细描述了采自中国重庆自流井组东岳庙段的杨氏璧山上龙2 ) (董枝明 ,1 980 )。愈合情况不好的椎体和椎弓以及耻骨的边缘形态表明 ,杨氏璧山上龙的正型标本是一个幼年个体的头后骨架。我们的研究表明杨氏璧山上龙主要依分叉的荐肋为特征 ,而这一性状在初次发表时作为颈肋特征被描述。璧山上龙的其他特征包括侧扁的神经棘以及狭窄的乌喙骨和肱骨上有一个突。经过重新修理的标本显示 ,坐骨和耻骨相对的面呈沟槽状 ,这一现象表明它们之间的接触关系要较原来描述的情况复杂 ,是一种依靠软骨的连接 ,而非直接接触。本文对杨氏璧山上龙的腰带部分进行了重新复原。O’Keefe (2 0 0 1 )的支序分析支持将Plesiosauria二分为Plesiosauroidea和Pliosauroidea,后者包含两个科 :Pliosauridae和

RESTUDY OF BISHANOPLIOSAURUS YOUNGI DONG 1980, A FRESH WATER PLESIOSAURIAN FROM THE JURASSIC OF CHONGQING

Bishanopliosaurus youngi Dong, 1980 from the Jurassic Dongyuemiao Member of the Ziliujing Formation in Chongqing Municipality, China is redescribed in detail. The holotype of B. youngi is the postcranial skeleton of a young individual, but so far the most complete plesiosaurian fossil known from the Asian Jurassic. Our restudy indicates that B. youngi can be diagnosed by the bifurcated sacral ribs combined with the compressed neural spine, narrow coracoid, and the humerus with a peculiar projection. B.youngi is a valid taxon, but its phylogenetic relationships with other plesiosaurians remain uncertain mainly because of the lack of cranial features. Previous studies on the Dongyuemiao fauna and flora indicate that the sediments are of subtropical freshwater origin. The discovery of B. youngi added further information on the freshwater invasion of plesiosaurians. Freshwater plesiosaurians so far known are very fragmentary, but their wide geographic and temporal distributions suggest that the presence of plesiosaurians in freshwater environment was not uncommon in most of their history.