阿纳巴管为生活于寒武纪早期、具三射对称管栖疑难生物。文中通过对采自陕西南部宁强下寒武统宽川铺组阿纳巴管壳体SEM和岩石薄片的观察,并以对称性和矿物组成作为线索对阿纳巴管的系统学位置和生物属性开展了探索。通过对称性对比研究和骨骼矿物组成的研究,将阿纳巴管解释为珊瑚虫纲古老干支类群的化石代表,为现生六射珊瑚的祖先类群。根据阿纳巴管个体发育过程对称性的演变所提供的线索进一步认为以六射及其倍数对称为特征的现代六射珊瑚可能经过三射对称中间阶段,起源于圆形辐射对称的祖先。阿纳巴管为由圆形经三射向六射转变这一中间阶段的化石代表。此外,还对阿纳巴管的成岩模式以及生活方式开展了探索性研究。

Anabarites is a representative of Early Cambrian tri-radially symmetrical tubecolous organisms with unknown affinity, although it has been speculated as sperpulid worm or as cnidarian with possibly scyphozoan affinity. The present SEM and TEM observation of the phosphate specimens from Lower Cambrian Kuanchuanpu Formation, Ningqiang, southern Shaanxi however reveals a number of diagenetic features of their exoskeleton, which allows to drawn a conclusion of their original mineral composition as aragonite. Ontogenic transition from circular to tri-radial symmetry in Early Meishucunian form and from tri-radial to hexa-radial symmetry in the forms from younger Lower Cambrian strata indicates that a stepwise evolutionary change of circular-radial, tri-radial toward hexa-radial symmetry already evolved in Early Cambrian Anabarites lineage. The hexa-radially symmetrical, extant hexacoralian Anthozoa may have been descending from the circular-radially symmetrical ancestor symmetry through Anabarites-like, tri-radially symmetrical intermediate form. Although the naked crown lineage group of hexacoralians may have evolved in a deep time, the first appearance of aragonitic exoskeleton is far back until Middle Triassic. Anabarites may represent a stem lineage group of hexacoralians and the presence of aragonitic exoskeleton in Anabarites may suggest that the protein molecules in determining the formation of aragonitic exoskeleton of the crown lineage hexacoralian corals may have evolved in Early Cambrian. Life habitat of Anabarites is also speculating and its mass occurrence with micromat-stabilized sea bed suggests that the animal is sessile, with its narrow end attaching to the micromat-stabilized sea bed.

Q915.813.3

国家自然科学基金委员会重点基金项目(No.40132010)和国家科技部重大基础项目(G20007700)资助课题.