Acrothoracican bioerosion as evidence of Early Cretaceous barnacles (Cirripedia) in northwestern Gondwana

Ichnofossils preserved in hard substrates are sometimes the only evidence documenting the presence of certain groups of organisms within past ecosystems. The Early Cretaceous marine ecosystems of northwestern Gondwana (present-day Colombia) were highly diverse, comprising vertebrates, invertebrates and microorganisms. Despite this paleobiodiversity, no fossils or ichnofossils ofbarnacles (Cirripedia) have previously been reported from this region of South America. Here, I describe the first record of barnacle sclerobionts from the Early Cretaceous (Valanginian) of northwestern Gondwana, represented by 132 borings tentatively assigned to cf. Rogerella, preserved on a complete shell of the gryphaeid Ceratostreon boussingaulti, from the Rosa Blanca Formation in Zapatoca, Colombia. The borings exhibit an inverted, inequilateral pyramidal chamber in three dimensions, triangular in transverse section, with the deepest point located in the posterior part of the chamber. This discovery underscores the significance of detailed ichnological analyses for reconstructing the complexity of ancient benthic interactions and elucidating the ecological strategies of sessile suspension feeders through geologic time.