Did stalked echinoderms bioerode calcareous substrates? A possible boring crinoid attachment structure in a stromatoporoid from the early Silurian (Telychian) of Estonia

A crinoid attachment structure has been found with its radices extending into the skeleton of a stromatoporoid ( Clathrodictyon variolare ) from the Adavere Regional Stage of Estonia (early Silurian, Telychian). This boring made by a crinoid is provisionally assigned to the ichnogenus Podichnus . The crinoid likely used chemical means for boring into the calcareous substrate. It is not known how common this phenomenon is in crinoids. Cutting into the calcareous substrate increases the crinoid’s contact with its substrate and makes the crinoid attachment much firmer than simple encrustation. Such firm attachment would have had adaptive value for crinoids and this strategy would be particularly advantageous in high-energy, turbulent settings such as biostromes and bioherms.