A Karethraichnus boring on a turtle shell bone from the Miocene of Italy is assessed as the attachment scar of a platylepadid symbiont

Among the turtle and whale barnacles, those included in the family Platylepadidae are mostly found partly embedded in the carapace and plastron of sea turtles. As a likely consequence of their fragile shell, the fossil record of these cirripede epizoans of marine chelonians is currently limited to two occurrences of Platylepas in Pleistocene strata. Here, we describe and refer to Kare-thraichnus cf. lakkos an isolated boring on a fossil cheloniid costal plate from the upper Miocene Arenaria di Ponsano Formation of Tuscany (central Italy). A scrutiny of palaeontological and neonto-l­ogical­literature­as­well­as­new­first-­hand­observations­reveal­that­this­boring­was­most­likely­pro-duced by a platylepadid barnacle similar to Stomatolepas, Stephanolepas or Platylepas. Two other probable platylepadid attachment scars, both of which incise cheloniid shell bones, are noted from the­Oligocene­and­Miocene,­respectively.­On­the­whole,­these­scanty­data­support­the­hypothesis­that-platylepadids­have­ancient­evolutionary­roots­and­a­long­story­of­symbiosis­with­sea­turtles.­Future-research­efforts­in­this­field­should­focus­on­1)­further­investigating­the­potential­of­bone­damage­of-turtle­ dwelling barnacles; 2) initiating a methodical quest for possible platylepadid attachment scars in Cenozoic marine turtle fossils; and 3) replenishing the still fragmentary Palaeogene fossil record of Coronuloidea.