AN EARLY JURASSIC TALPINA-DOMINATED ASSEMBLAGE OF BORINGS IN BIVALVE SHELLS FROM SOUTHERN HUNAN, CHINA, WITH REMARKS ON THE ICHNOGENUS TALPINA HAGENOW, 1840
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Abstract:
An assemblage of borings in bivalve shells is described from shallow-marine deposits of the upper Xintianmen Formation (Early Jurassic, early Sinemurian) near Xiaping, Yizhang County, south-eastern Hunan Province, southern China. Talpina hunanensis ichnosp. nov., a new ichnospecies of borings constructed by Phoronida, clearly dominates this ichnocoenosis. Other borings occasionally co-occurring with T. hunanensis comprise Rogerella ichnosp. (produced by acrothoracican Cirripedia), Calcideletrix ichnosp. (probably bored by algae), microborings of algae or fungi which may preliminarily be assigned to " Mycelites " ichnosp., and an unidentified type of boring possibly caused by sponges. The bioeroders infested larger bivalve shells that were exposed on the seafloor. The borings are preserved as natural casts (Steinkerns) in the voids left after dissolution of the aragonitic host shells. In addition, the ichnogenus Talpina Hagenow, 1840 is discussed, especially with regard to the often difficult differentiation of ichnospecies, and its diagnosis is emended.
