A new type of Olivooides mirabilis from the Cambrian Kuanchuanpu Formation (Fortunian Stage, Terreneuvian Series), Ningqiang, Shaanxi Province
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Abstract:
Three-dimensionally phosphatized small shelly fossils with phylogenetic affinities of multiple animal phyla from the Fortunian strata of the Cambrian witnessed a pivotal evolutionary episode in the Cambrian Explosion. Olivooides is a morphologically distinctive and easily identifiable taxon in the small shelly fossil Anabarites trisulcatus–Protohertzina anabarica assemblage zone with a widely accepted phylogenetic placement within the Cnidarian. The great majority of Olivooides fossil specimens reported in the last 40 years have been primarily assigned to two species: O. multisulcatus and O. mirabilis. Morphological disparity and growth mode of Olivooides, however, need further study for better clarification. Here we describe phosphatized Olivooides fossils from the basal Cambrian Kuanchuanpu Formation (Fortunian Stage, Terreneuvian Series) at the Yuanbaoshan section in Ningqiang County, southern Shaanxi Province, South China. We report a new type of Olivooidesmirabilis, characterized by only one transverse band in the embryonic tissue, five rows of tightly and sharply arranged longitudinal folds in the post-embryonic tissue, and two sets of oral lobes with two distinct degrees of folding. The distinct features between the new and the traditional O. mirabilis may represent intraspecific variation. The new fossil material adds to the diversity of Olivooides and sheds palaeobiological as well as embryological insights into our understanding of these enigmatic fossils in the earliest Cambrian Period.
