AN EARLY CAMBRIAN PROBLEMATIC ORGANISM (ANABARITES) AND ITS POSSIBLE AFFINITY

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.

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Clc Number:

Q915.813.3