贵州晚三叠世关岭鱼龙的原始尾弯对比研究

True Tailbend Occurred in the Late Triassic: Evidence from Ichthyosaur Skeletons of South China

通过对贵州关岭上三叠统卡尼阶法郎组瓦窑段地层中的两件关岭鱼龙属标本的观察、测量,并与早侏罗世鱼龙标本对比研究,发现晚三叠世的关岭鱼龙尾椎中部存在一定数量形态发生变化的侧视呈梯形的椎体,已经具有了传统观点认为只在侏罗纪和白垩纪鱼龙中出现的尾弯,弯角为15°左右(侏罗纪鱼龙尾弯弯角可达60°)。这一衍生性状的出现表明晚三叠世关岭鱼龙已经在一定程度上具有了鼎盛时期鱼龙所拥有的尾鳍,并已获得了较强的游泳能力,开始成为完全适应远洋快速游泳的生物,并将以前认为截然分离的三叠纪的早期鱼龙类群与侏罗纪-白垩纪鼎盛时期特化的鱼龙类群联系起来,是鱼龙目单系起源的又一例证。

Here the true tailbends are reported in two complete skeletons of Guanlingsaurus from the late triassic of Guizhou Province, southwestern China after accurate observations, measurements and comparisons with Ichthyosaur of early jurassic. They have acquired the wedge-shaped centra and the angles in these tailbends are around 15° while those in jurassic types are around 60°. This study shows for the first time that wedge-shaped tailbend centra already existed in merriamosaurs as early as late triassic time, probably being a result of coevolution between ichthyosaurs and the environment. The occurrence of the true tailbend connected triassic and jurassic ichthyosaurs that used to be considered as separate groups in previous literature. The present finding also suggests the monophyly of ichthyopterygia.