Occurrence of the Enigmatic Bivalved Fossil Apistoconcha in the Lower Cambrian of Southeast Shaanxi, North China Platform
Occurrence of the Enigmatic Bivalved Fossil Apistoconcha in the Lower Cambrian of Southeast Shaanxi, North China Platform
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DOI：
10.1666/13-078
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发表时间：
2014-04
期刊：
影响因子：
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通讯作者：
Guoxiang Li;Zhifei Zhang;H. Hua;Huining Yang
中科院分区：
文献类型：
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作者：
Guoxiang Li;Zhifei Zhang;H. Hua;Huining Yang
摘要早寒武世钙质骨骼化石ApistoconchaConwayMorris的特征是两个壳瓣，壳瓣上有后齿和脐腔。在澳大利亚、蒙古和格陵兰的下寒武统博托米阶碳酸盐岩中也有报道。本文报道了华北地台陕西省东南部洛南地区下寒武统新集组中一新发现的隐壳类化石。根据新集组的材料（5个腹瓣和4个背瓣），Apistoconcha cf.系统地描述了隐壳类的系统分类，并讨论了隐壳类在分类上的亲缘关系。后壳类的壳具有一个两侧对称的“前后”平面，其两个瓣显然在生活中有关节连接，尽管齿状结构和凹陷分别与喙状腕足动物或杯足动物的双瓣壳的牙齿和插座几乎没有相似之处。隐壳类不能被分配到腕足类或软体动物的冠组，即使功能形态分析表明，隐壳类可能是一个“茎组腕足类”。与隐壳类不同，形态上相似的Tianzhushanella Liu仅从单一类型的瓣膜中发现，缺乏后齿和凹窝。天柱山虫可能代表单壳动物或双壳动物，其中另一个瓣尚未确定。尽管Apistoconcha和Tianzhushanella都可能代表茎群腕足动物，但它们可能对应于腕足动物进化的不同阶段。因此，将隐壳纲和天柱山属归入同一科（天柱山属）可能会模糊它们的生殖意义。
Abstract The early Cambrian calcareous skeletal fossil Apistoconcha Conway Morris is characterized by its two valves having posterior teeth and internal umbonal cavities. It has been reported from lower Cambrian Botomian-equivalent carbonate rocks in Australia, Mongolia, and Greenland. Here we report a new occurrence of Apistoconcha in the lower Cambrian Xinji Formation of Luonan, southeast Shaanxi Province, North China Platform. Based on material (five ventral and four dorsal valves) from the Xinji Formation, Apistoconcha cf. apheles is systematically described and the taxonomic affinity of Apistoconcha is discussed. The shell of Apistoconcha possesses an ‘antero-posterior' plane of bilateral symmetry, and its two valves apparently articulated in life, although the tooth-like structures and pits show little resemblance to the teeth and sockets, respectively, of bivalved shells of rhynchonelliform brachiopods or pelecypods. Apistoconcha cannot be assigned to the crown groups of either brachiopods or mollusks, even though functional morphological analysis indicates that Apistoconcha may be a ‘stem-group brachiopod'. Unlike Apistoconcha, the morphologically similar Tianzhushanella Liu is known only from a single type of valve lacking posterior teeth and pits. Tianzhushanella may represent either a univalved animal or a bivalved animal, the other valve of which has not yet been identified. Even though both Apistoconcha and Tianzhushanella may represent stem-group brachiopods, they probably correspond to different stages of brachiopod evolution. Thus assignment of Apistoconcha and Tianzhushanella to the same family (Tianzhushanellidae) may obscure their phylogenic implications.