Evidence of †Yuskaichthys in Early Late Cretaceous/Paleocene Deposits from the Cochabamba-Potosí Basin Extends Both Geographical and Time Range of this Extinct Pimelodoidea Catfish

Abstract

The fossil genus †Yuskaichthys, previously known only from Eocene deposits in Argentina, is here identified based on three isolated parieto-supraoccipital bones collected in the Tiupampa locality (Bolivia). This discovery notably extends both the geographic and temporal distribution of the genus into the early Paleocene. Morphological features such as the bifid posterior margin of the supraoccipital process, distinctive longitudinal grooves continuing along the process, and transverse pit lines support its taxonomic assignment to †Yuskaichthys. These fossils, were compared via micro-CT imaging with extant and extinct pimelodid catfish, revealing key synapomorphies of the clade Pimelodoidea. The occurrence of †Yuskaichthys in both Tiupampa (Bolivia) and Maíz Gordo (northwestern Argentina) highlights paleobiogeographic connectivity between central South American basins during the Paleocene, consistent with regional fluvial systems associated with the Andean foreland basin evolution. This finding not only sheds light on early siluriform diversification but also supports hypotheses of a Late Cretaceous radiation of modern catfish lineages. Additionally, it underscores the resilience and dispersal of freshwater fish faunas following the Cretaceous–Paleogene extinction event. Overall, these results contribute significantly providing new data to the understanding the South American Paleogene ichthyofaunas and their paleoenvironmental and paleogeographic context.

Keywords: Yuskaichthys, Siluriformes, Paleocene, Bolivia, Catfish, Fossil record