我国西南地区中三叠世安尼期龙鱼属(Saurichthys)一新种（英文）

A new species of Saurichthys from the Middle Triassic(Anisian) of southwestern China

作为一类高效的捕食者,龙鱼跻身中生代早期水生生态系统中的重要消费者。我国西南地区中三叠世安尼期的化石群中,龙鱼类在形态和分类上呈现出显著的多样性。报道了云南安尼期罗平生物群的龙鱼属(Saurichthys)一新种,它代表着龙鱼在椎骨结构和基本体型上的新变化。披刺龙鱼(新种)(Saurichthys spinosa sp. nov.)是一种小型龙鱼,其特征包括:颅顶部的眶间区(interorbital region)非常狭窄;匙骨前端膨大而腹侧呈拱状;椎骨偏大且无神经棘,侧向伸展的副神经板(paraneural plate)在躯椎里交替出现;奇鳍鳍条数量较少;体表具两列平行的披强壮棘刺的针状侧鳞。与同属其他种类相比,S. spinosa头部及躯体轴上部的高度明显减缩以致体高变小。体内侧向延长并插入水平膈的副神经板与体表刚性互锁的双排侧鳞使得整个鱼体非常僵硬,这与其体节(椎骨)数目的减少在功能上具有一致性。这一发现揭示了龙鱼类中轴骨骼结构及其体型流体力学特质的多样化。综合同时期龙鱼类在运动方式和摄食机制的创新,这些因素可能促成了安尼期东特提斯洋龙鱼类的爆发式演化,而这正是二叠纪末大绝灭后生物圈复苏过程中快速辐射阶段的一个缩影。

The saurichthyiform fishes were effective predators and hence the significant consumers in the aquatic ecosystems during the Early Mesozoic. They showed a notable diversification in the Anisian（Middle Triassic） Lagerst？tten of southwestern China. In this contribution, we report a new species of Saurichthys from the Anisian of Yunnan, China, that displays some peculiar modifications of the axial skeleton and the longate body of the group. This new species, Saurichthys spinosa is a small-sized saurichthyid fish characterized by a very narrow interorbital region of the skull roof, an anteriorly expansive and ventrally arched cleithrum, proportionally large abdominal vertebrae lacking neural spines and alternately bearing laterallystretching paraneural plates, few fin rays in the median fins, and two paralleling rows of needlelike flank scales with strong thorns. This fish has slimmed down the body by reducing the depth of the head and the epaxial part of the trunk. The elongate paraneural plates inserted in the horizontal septum and the rigid interlocking of the flank scales render the fish a very stiff body, which is compatible with the functional consequence of the obvious decrease of the body（vertebral） segments. This discovery reveals the variability of the axial skeleton and the hydrodynamic properties of the saurichthyiform fishes. These factors, together with the innovations in the locomotion and feeding habit, might have intrinsically effected the evolutionary burst of the eastern Tethyan saurichthyiform fishes during the Anisian, a marked signature of the rapid radiation stage of the biotic recovery after the end-Permian extinction.