Abstract:

The Early Emsian Event (E’Em Event), the most significant bio-event for Chinese Devonian vertebrates, has significantly impacted on the diversity of galeaspids. The endemic Galeaspida almost became extinct after the Mid-Emsian Event (M’Em Event). Only few galeaspid taxa survived from these events, such as Clarorbis apponomedianus from the Eifelian of Guangxi, South China, and an indeterminate galeaspid from the Frasnian of Ningxia, Northwest China. Here, we report the first Middle Devonian galeaspid, Dongfangaspis sp., from the Haikou Formation in Wuding, Yunnan Province. The new material is more suggestive of the type species of Dongfangaspis, D. major, than Laxaspis and Polybranchiaspis in its suborbicular headshield with small inner cornual process, broad and nearly aequilate ventral rim, and about 45 pairs of branchial fossae. Dongfangaspis bears the largest number of branchial fossae ever recorded in galeaspids, which probably play an important role in Dongfangaspis surviving from the E’Em and M’Em events. The new finding represents the second Middle Devonian fossil record of galeaspids, and extends the chronological range of Dongfangaspis from the Pragian (Early Devonian) to the Eifelian (Middle Devonian).

Key words: Wuding, Yunnan, Middle Devonian, Haikou Formation, galeaspid, E’Em Event

摘要：

早埃姆斯期生物事件是中国泥盆纪脊椎动物演化过程中最重要的生物事件,对盔甲鱼类的生物多样性产生了重大影响。在埃姆斯期之后,具有浓厚区域性色彩的盔甲鱼类几乎灭绝,只有少数属种遗存,如发现于华南广西中泥盆统艾菲尔阶的近中显眶鱼(Clarorbis apponomedianus)以及西北宁夏上泥盆统弗拉阶的一个多鳃鱼类未定种。首次报道了产自云南省武定县海口组的第一个中泥盆世盔甲鱼——东方鱼未定种(Dongfangaspis sp.)。与宽甲鱼(Laxaspis)和多鳃鱼(Polybranchiaspis)相比,这件新标本呈现出明显的东方鱼属的特征：近圆形的头甲,内角小,腹环宽且近乎等宽,约有45对鳃囊。东方鱼具有有史以来数目最多的鳃囊,这可能帮助它们在早、中埃姆斯期生物事件中幸存下来。这一新发现也是第二个中泥盆世盔甲鱼类化石记录,并将东方鱼属的生存时代从早泥盆世布拉格期扩展到了中泥盆世艾菲尔期。

关键词: 云南武定, 中泥盆世, 海口组, 盔甲鱼类, 早埃姆斯期生物事件