Miocene Decapod Crustacean Fauna of Tierra Del Fuego, Argentina, Signals Timing of Establishment of Modern Biogeographic Provinces

A diverse assemblage of anomuran and brachyuran decapod crustaceans from the Miocene Carmen Silva and Cabo Domingo formations in eastern Tierra del Fuego, Argentina, marks the first robust decapod fauna from that region. Oligocene and Miocene decapod assemblages in southern Argentina and Chile typically are characterized by two genera, Chaceon and Proterocarcinus, both Miocene endemics to the region. However, the associated decapods are different in each different assemblage. In general, the faunas of Chile and Andean Argentina are similar, and they differ from correlative exposures along the Atlantic margin of Argentina. Within the Carmen Silva Formation, Chaceon and Proterocarcinus are associated with at least two thalassinid genera, an anomuran porcellanid, and a small xanthoid. The porcellanid is remarkable because it occurs in very large numbers, often found in small concretionary structures as a virtual coquina. In the Cabo Domingo Formation, Chaceon and Proterocarcinus are associated with callianassids, a species of Asthenognathus, a larger xanthoid, and other species. Comparing the Tierra del Fuego faunas with those from the late Oligocene and Miocene Atlantic and Pacific sides of southern South America suggests a weak association with Chilean and Andean faunas; however, the overall assemblage suggests that the region of Tierra del Fuego formed a separate faunal province characterized by altogether different taxa along with the more wide-ranging Chaceon and Proterocarcinus. Thus, the modern decapod faunal provinces in southern South America had been established by late Oligocene or Miocene time. Field work was supported by NSF EF 0531670 to Feldmann and Schweitzer.