A fossil carbonate rocky shore in the Kalcit Quarry: a new insight into echinoid shallow marine bioerosion (Miocene; Czech Republic)

A Miocene fossil rocky coastline is well preserved in Kalcit Quarry near Brno. It differs from the few preserved coeval coastlines of the Central Paratethys in the dominance of borings attributable to echinoids. These borings are represented by roughly smooth shallow circular pits interpreted as dwelling traces of echinoids. Ichnotaxonomically, they can be placed in the ichnospecies Circolites kotoucensis Mikuláš, 1992. Besides usual individual pits, two discernible varieties of composite Circolites were found: (1) linear chains of pits interconnected by a smoothed joint bottom; and (2) spirally folded pits resembling a rosacean flower. The linear chains are morphologically very similar to narrow forms of Planavolites homolensis Mikuláš, 1992 and to Ericichnus bromleyi Santos and Mayoral, 2015. This similarity demonstrates the necessity of a review of the diagnoses of all the hitherto described ichnogenera attributed to boring echinoids, i.e., Circolites, Ericichnus, and Planavolites. We suggest that linear or planar traces with smoothed bottoms should be considered a composite of neighbouring Circolites, provided that the remains of individual pits are still discernible in the ground plan. Ericichnus is now considered as junior synonym of Planavolites Mikuláš, 1992.