Symbiotic association of a pyrgomatid barnacle with a coral from a volcanic middle Miocene shoreline (Porto Santo, Madeira Archipelago, Portugal)

Abstract

The bioclaustration of the pyrgomatid barnacle Ceratoconcha aff. costata withthe carbonate skeleton of a colonial hermatypical coral (Tarbellastrea reussiana) is described from a middle Miocene basaltic rocky palaeoshore on a small north-eastern Atlantic islet of Porto Santo (Madeira Archipelago, Portugal). The resulting structure is named as a new trace fossil Imbutichnus igen. nov., characterized by a small, funnel-like cavity, a circular to oval cross-section, with a nearly cylindrical shape the upper part and a conical shape towards the base. Imbutichnus costatum isp. nov. is defined as a bioclaustration structure produced by the overgrowth of a pyrgomatid barnacle by a coral. From an ethologic point of view, Imbutichnus is attributed to the Impedichnia category. terms of palaeoecology, it is interpreted as the result of a parasitic relationship. This is also the oldest record of pyrgomatid barnacles the eastern Atlantic and clearly demonstrates that the Miocene palaeogeographic range of Ceratoconcha was much wider than previously assumed. © The Palaeontological Association.