广西南宁下泥盆统华南鱼类化石新发现及其地层和古地理意义*

笔者描述了广西南宁下泥盆统布拉格阶那高岭组下部盔甲鱼类的新发现,建立了华南鱼科2个新种——丘比特华南鱼(Huananaspis cupido sp. nov.)和梁氏亚洲鱼(Asiaspis liangi sp. nov.)。前者以头甲个体较小、不发育中背棘、两角末端超出头甲后缘等特征区别于属型种武定华南鱼(H. wudingensis),后者以头甲长大于宽、角向头甲侧后方延伸、角后缘发育锯齿、中背孔呈纵长椭圆形等特征区别于属型种宽展亚洲鱼(A. expansa)。广西南宁地区那高岭组具有可靠的地质时代证据,其中所产的徐家冲鱼类化石组合能够为华南地区早泥盆世地层的对比研究提供鱼类化石标准,而华南鱼属(Huananaspis)和亚洲鱼属(Asiaspis)在那高岭组的发现,丰富了华南鱼类的多样性,扩大了徐家冲鱼类组合的化石内容,并为云南武定坡松冲组与广西南宁那高岭组之间的对比提供了直接化石证据。广西南宁莲花山组与那高岭组过渡层中的徐家冲鱼类化石组合物种多样性最高,几乎涵盖了其他地区该组合的所有属种,说明广西南宁地区可能是盔甲鱼类辐射和扩散的中心之一。该地区早泥盆世布拉格期的古鱼类、早期维管植物和腕足动物均表现出显著的地方性色彩,可能跟华南海是一个半封闭的陆表海湾有关,即由于封闭海效应,鱼类在这个封闭的环境中独立演化,表现出很高的多样性和很强的土著性,最终在华南板块上形成一个独立的动物区系——“盔甲鱼—云南鱼”动物区系。

New findings of huananaspid fishes from the Lower Devonian in Nanning,Guangxi and their stratigraphic and biogeographic significances

Two new species of Huananaspidae(Huananaspidiformes,Galeaspida),Huananaspis cupido sp. nov. and Asiaspis liangi sp. nov.,are described from the lower part of the Nagaoling Formation(Pragian,Early Devonian)in Nanning,Guangxi,China. H. cupido sp. nov. differs from H. wudingensis in smaller headshield,lacking median dorsal spine,and cornual processes extending beyond the posterior margin of the headshield. A. liangi sp. nov. differs from A. expansa in headshield length greater than width,cornual processes extending posterolaterally,serrated posterior margin of cornual processes,and longitudinal oval median dorsal opening. The Nagaoling Formation yields reliable index fossils indicating a Pragian age,thus the Xujiachong vertebrate assemblage yielded from this formation can provide a palaeoichthyological standard for stratigraphic correlations of Early Devonian in South China. New findings of Huananaspis and Asiaspis from the Nagaoling Formation enriches the biodiversity of huananaspids,adds new members to the the Xujiachong vertebrate assemblage,and provides direct fossil evidence for the correlation between the Posongchong Formation in Wuding of Yunnan and the Nagaoling Formation in Nanning of Guangxi. The Xujiachong vertebrate assemblage is the most diversified in the transitional beds between the Lianhuashan and Nagaoling formations,almost containing all genera in adjacent regions,indicating that Naning of Guangxi is one of the centers for galeaspids radiating and dispersing. Fish assemblage displays a similar high level of endemism to that of the vascular plants and brachiopod fauna during the Pragian of Early Devonian,which probably caused by the South China sea,a large semi-closed epicontinental gulf. Because of the effect of a closed sea,fishes show exceptional taxonomic diversity and high levels of endemism,forming an independent biogeographic region known as‘galeaspid-yunnanolepid province’ in South China.