湖南中泥盆统跳马涧组中华沟鳞鱼再研究

Reappraisal of Bothriolepis sinensis Chi,1940 from the Tiaomachien Formation,Hunan,China

计荣森先生于1940年基于湖南长沙附近中泥盆统跳马涧组采集到的一些以前中背片为代表的胴甲鱼类标本命名了中华沟鳞鱼(Bothriolepis sinensis),这是在中国正式命名的第一种古生代脊椎动物。虽然卢立伍于1988年对后续出产于模式种产地的其他中华沟鳞鱼材料进行了补充描述,但研究者对中华沟鳞鱼的形态学特征和系统发育仍缺乏全面认识。在此基于计荣森先生所采集的样本及一些收藏于中国地质博物馆未正式发表的化石,对中华沟鳞鱼进行了再研究,补充了其头部与躯甲的部分特征。与其他沟鳞鱼类相比,中华沟鳞鱼拥有以下一系列特征:较大的听上加厚区、颅顶甲长宽比1.4-1.6、较宽的眶窗(宽于颅顶甲的1/3)以及扇形的眶前凹等。系统发育分析结果显示,B.askinae并非位于沟鳞鱼支系的最原始位置;中华沟鳞鱼与广东沟鳞鱼因同样拥有纤细的附肢近端(长宽比大于7)而形成了一个稳定的单系。本研究中绝大部分的中国种类均位于同一支系上,该支系的共有衍征为其胸鳍感觉管从第一腹中片延伸至第二腹中片。此外,基于“深骨”平台数据的古生物地理可视化分析结果表明,沟鳞鱼类最早于艾菲尔期出现在华南与东冈瓦纳,并迅速地辐射并扩散至全球,最终于法门期在瑞亚克洋两岸表现出了高度的物种多样性。

Bothriolepis sinensis Chi 1940,mainly based on anterior median dorsal plates from the Middle Devonian Tiaomachien Formation of Hunan,is the first Paleozoic vertebrate taxon erected in China.Although additional materials of B.sinensis from the type locality were described by Lu in 1988,its morphology and phylogeny remain poorly understood.In this study,we complemented the morphology of the skull and trunk armor of B.sinensis based on Chi’s specimens housed in the Institute of Vertebrate Paleontology and Paleoanthropology,Chinese Academy of Sciences,and several previously undescribed specimens in the Geological Museum of China.Bothriolepis sinensis differs from other Bothriolepis in the following combination of characteristics:enlarged supraotic thickening,length/width ratio of head shield 1.4-1.6,broad orbital fenestra(greater than 1/3 of the head shield width),and fan-shaped preorbital recess.The phylogenetic analysis did not place B.askinae in the most basal position of the genus and revealed that B.sinensis and B.kwangtungensis consistently from a monophyletic group characterized by their slender proximal segment of the pectoral fin(length/width ratio greater than 7).A majority of Chinese Bothriolepis species(B.niushoushanensis,B.lochangensis,B.tungseni,B.kwangtungensis and B.sinensis)were clustered in a clade characterized by the pectoral pit-line on the ventral central plate 1 extending to the ventral central plate 2.The paleogeographic reconstruction using the data from the DeepBone platform showed that Bothriolepis had its oldest occurrences in South China and East Gondwana in Eifelian,dispersed rapidly worldwide,and then diversified across the coasts of the Rheic Ocean.