New findings of galeaspids (Agnatha) from the Lower Devonian of Qujing, Yunnan, China

分类： 生物学 >> 动物学 提交时间： 2017-11-07 合作期刊: 《古脊椎动物学报》

LIU Yu-Hai GAI Zhi-Kun ZHU Min

摘要： New findings of galeaspids (Agnatha) including Altigibbaspis huiqingae gen. et sp. nov., an indeterminate polybranchiaspid, Eugaleaspis changi, and Nanpanaspis microculus are described from the lower part of the Xishancun Formation (early Lochkovian, Early Devonian) near the northeast entrance of Liaokuo Park, Qujing City, Yunnan Province, China. The Polybranchiaspis-like new genus is characterized by a blade-like median dorsal ridge on the dorsal side of head-shield. The morphological disparity of the median dorsal ridge and spine in galeaspids suggests that these structures functioned more than providing a hydrodynamic stability. We assume that a high upright and compressed spine may render galeaspid fishes an apparently larger size as seen by a predator, and a blade-like median dorsal ridge may accomplish a defense against the claws of large sea scorpions. Nanpanaspis is peculiar in bearing two short laterally projecting processes on each side of the head-shield, and its phylogenetic relationship is discussed based on different interpretations on the homology of these processes. Considering the unique morphology of Nanpanaspis, and its early occurrence among the Huananaspiformes, we assign Nanpanaspis in the monogeneric family Nanpanaspidae to represent an early branch of the Huananaspiformes.

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