Valanginian and Hauterivian bochianitid ammonoids from the Rosa Blanca Formation of Colombia: Palaeobiogeographic implications

The Lower Cretaceous record of heteromorph ammonoids in northern South America is still poorly known, occurrences are often mentioned only without detailed analysis of their morphology and palaeobiogeographic implications. Here, we describe the first occurrence of Bochianites neocomiensis from the Valanginian of northern South America. This finding is from the upper Valanginian section of the Carrizal Member of the Rosa Blanca Formation. It underlines the meaning of high amplitude late Valanginian sea level rise, and related opening of migration routes, as part of the Weissert Event. Additionally, we identify Janenschites oosteri from the lower Hauterivian El Sapo Member, also within the Rosa Blanca Formation in the Zapatoca region of Colombia. The presence of B. neocomiensis and J. oosteri in Colombia broadens the palaeobiogeographical record for these species to northern South America, both trace the improving migration routes for ammonoids along the margins of the South American continent during the course of the Early Cretaceous.