First record of Cheirocrinus penniger (Eichwald, 1842) (Cystoidea) from the Ordovician Miaopo Formation in western Hubei, China
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Abstract:
The Miaopo Formation of the Middle–Upper Ordovician transition in western Hubei Province of China, is a few meters thick and composed of shales intercalated with thin-bedded bioclastic limestones. It was deposited in an intra–platform depression with marine–floor depth below major wave-base of the Yangtze Epicontinental Sea. The unit is high bio-diversity and has an abundance of macrofossils. We report for the first time on Cystoidea fossils from the shales in the mid-upper part of the Miaopo Formation at Chenjiahe section of northern Yichang, and Zhenjin section of Yuan’an County. Based on the co-occurred graptolitic faunas, the units yielding more than 30 Cystoidea fossils are assigned to the Nemagraptus gracilis Biozone of the basal Sandbian, Upper Ordovician. Cystoidea fossils are morphologically identified and described as Cheirocrinus penniger (Eichwald, 1842). In taphonomic aspect, the C. penniger fossils from the Zhenjin section are dominated by aggregated and compressed calyx plates, including a complete specimen with column preserved. Same species from the equivalent horizon at the Chenjiahe section are single disarticulated calyx plates. The Cheirocrinus was a cosmopolitan genus in the Ordovician. Cheirocrinus of the present discovery expands the temporal and spatial distribution of the genus, i.e. from the Early Ordovician Tonggao Formation (slope facies) to the Late Ordovician Miaopo Formation (intra-platform depression) in the South China Block.
