First record of bioeroding barnacles (Cirripedia: Acrothoracica) on ammonite shells

Abstract

Oval, elongated and radially orientated pits were found on specimens of a Kimmeridgian (Upper Jurassic) aspidoceratid ammonite species from Páskom Hill (Bakony Mountains, Transdanubian Range, Hungary). These trace fossils most probably represent acrothoracica (burrowing barnacles) borings, which have never been documented on ammonites before, and are described here as Paskomella acanthicola nov. igen. et nov. isp. The tiny barnacles were living together with the cephalopods; therefore, these trace fossils represent a new type of commensalism between the ammonites and the boring, host-specific, acrothoracid cirriped.