Lower Cambrian anabaritids from south China

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Abstract
Anabaritids are a distinctive group of early skeletal fossils, with tri-radially symmetrical tubes. They occur in the earliest Cambrian deposits, and seem to be especially characteristic of the Tommotian strata and putative pre-Tommotian units (e.g. Manykay horizon). A detailed redescription ofAnabarites rotundusQian from near Kuanchuanpu, Shaanxi Province emphasizes the degree of morphological variation. New data on shell composition suggest a bilayered structure, the outer unit composed of fibres parallel to growth lines, overlying a distinctive inner lamella with a chevron ultrastructure. Tentative evidence for anabaritids possibly being operculate is presented, the putative operculum being a simple convex disc. More poorly preserved anabaritids from the Yangtze Gorges (Hubei Province) and Meishucun (Yunnan Province) are referred toA. trisulcatus. All these Chinese occurrences of anabaritids are consistent with a lower Tommotian age of the associated faunas, but reliable and precise correlations with other Precambrian-Cambrian boundary sections remain inconclusive.