BIOGEOGRAPHY OF MIOCENE CHILEAN AND ARGENTINE DECAPODS

Miocene Decapoda from southern South America are hypothesized to have been affected by dynamic, local climates. Fossil decapods from Chile have been previously studied but new samples in this study contain new decapod species. The specimens in the study were collected by R.M. Feldmann and L. A. Chirino-Gálvez from several Eocene-Miocene coastal locations in Chile. The Miocene Chilean fossil decapod fauna was compared to the Miocene Argentine fossil decapod fauna. To compare the two faunal groups, all specimens were identified from Chile and a completed faunal list, including any new species from this study, was created to use for a comparative analysis of the two faunal groups. The species in this study represent nine genera within six superfamilies: Grapsoidea, Montezumelloidea, Pilumnoidea, Pinnotheroidea, Portunoidea, and Raninoidea. The Miocene decapod faunas from both Chile and Argentina showed some similarities. The Chilean decapod fauna shares some genera with the Argentine decapod fauna, despite having two different ocean system environments. The Chilean coast is dominated by the Humboldt Current which brings water from the Antarctic Circumpolar Current northward and along the coast, causing upwelling of cold, nutrient-rich water to the surface. Off Argentina’s coast, the Malvinas Current brings cold water north from the Antarctic Circumpolar Current which then collides with the Brazil Current, bringing warm water southward along the coast. The interaction of the Malvinas and Brazil Currents brings highly nutrient-rich waters to the surface through mixing. Similarities of the decapod fauna between Chile and Argentina indicate that during the Miocene, a migration event occurred, potentially driven by local climate change. The biogeographic ranges of the Miocene decapods from southern South America were analyzed to determine the migration routes. One of the trends may have been a forcing on the higher latitudes from the gradual cooling of the Miocene, which caused decapods to migrate to lower latitudes, maintaining an anti-tropical distribution for some taxa.