江西志留纪山口中华盔甲鱼的再描述

A redescription of the Silurian Sinogaleaspis shankouensis(Galeaspida,stem-Gnathostomata)from Jiangxi,China

基于对江西省修水县志留系西坑组发现的11个新标本的观察,对存在争议的山口中华盔甲鱼(Sinogaleaspis shankouensis)进行了重新描述。深入的形态学研究表明,山口中华盔甲鱼的侧线感觉管系统展示出基干盔甲鱼类、真盔甲鱼目、多鳃鱼目和华南鱼目等多个类群的镶嵌特征。山口中华盔甲鱼的侧线感觉管系统由4条纵行干管和6条横向联络管相互交叉在头甲背面形成格栅状分布,可能反映了脊椎动物的祖先状态。山口中华盔甲鱼在动物群上属于中华盔甲鱼–修水鱼组合或茅山组合,该组合可能代表了盔甲鱼类在志留纪兰多维列世特里奇期的第一次适应辐射。江西修水西坑组古沉积环境指示了一种低盐度半咸水的近海环境,可能是由于大量淡水从附近河流涌入导致盐度降低,而含鱼层位灰绿色泥质粉砂岩中含有的大量泥砾则指示鱼化石经历了短距离的河流搬运。因此,该生物群可能生活在埋藏区域上游的淡水河流里。

Sinogaleaspis shankouensis is redescribed based on 11 new specimens collected from the type locality of the Xikeng Formation in Xiushui county,Jiangxi Province.The in-depth morphological study indicates that the sensory canal system of S.shankouensis exhibits a mélange of characters of plesiomorphic galeaspid taxa,Eugaleaspiformes,Polybranchiaspiformes and Huananaspiformes.The grid distribution of the sensory canal system on the dorsal side of the head-shield,which comprises four longitudinal canals intercrossed with six pairs of transverse canals in S.shankouensis,probably represents a plesiomorphic condition of vertebrates.Sinogaleaspis shankouensis belongs to the Sinogaleaspis-Xiushuiaspis Fauna or the Maoshan Assemblage which represents the first diversification of galeaspids in the Telychian,Llandovery of the Silurian period.The sedimentary paleoenvironment of the Xikeng Formation in Xiushui,Jiangxi Province is suggestive of a brackish water environment,whereas a large sum of muddy gravels in fish-bearing sandstone beds point to a short distance of potamic transportation.This indicates that the Sinogaleaspis-Xiushuiaspis Fauna may live in a fresh water environment in the river rather than their burial area in the sea.