Cretaceous-Miocene isolation of South America: new biogeographic clues from insect inclusions of Miocene western Amazonia amber

PETRULEVICIUS, J. F. NEL, A., DE FRANCESCHI, D., GOILLOT, C., ANTOINE, P. O., SALAS-GISMONDI, R. Y FLYNN, J. J.

Bonn, Alemania

Congreso; 79 Jahrestagung der Paläontologischen Gesellschaft; 2009

Paläontologischen Gesellschaft

South America is considered a single biogeographic province from middle Lower Cretaceous to late Miocene. Its existence as an isolated region, a big island during more than 120 Ma, is proclaimed by plate tectonics investigations. Biotic relationships with other continents in this time lapse are not so clear and in many cases are based in external (tectonic) explanations. It is important to search for palaeobiogeographic hypotheses based on independent data to test those obtained through plate tectonics. Fossil insects could constitute such data sets. Neogene fossil insects are mainly unknown in South America. The recent discovery of the first inclusions in amber from South America is noteworthy. Contrary to this, arthropods included in fossilized resins in the Northern Hemisphere are reported from many sites from the Cretaceous to the Holocene. Pre-quaternary inclusions in amber were previously unknown in South America, except for the Holocene Colombian copal (< 1,000 years old). The Colombian copal has an extraordinary potential insect diversity to be studied. Previous to our present work, Miocene fossil insects were unknown in South America even from lacustrine outcrops. The Miocene amber of Western Amazonia has also a nice potential in a mainly unknown background of Early Neogene diversity. This amber comes from Pebas Formation near Iquitos in northeastern Peru at a latitude of 4° S. The amber-bearing level corresponds to a paleolake in the upper parasequence of the formation. The Pebas formation was deposited in a fluvio-lacustrine wetland that formed the precursor of the Amazon River system and originated in the Andes. The bearing strata of the amber are considered middle Miocene in age and result older that the connection of South America with Central America. Its situation at Western Amazonia gives us the record of an intertropical entomofauna previous to the latest Miocene-Pliocene land connection with Central and North America. Insects are diverse with 23 recognized families with normal bias for amber inclusions as the dominance of orders like Diptera and Hymenoptera and small sized specimens. A study of the entomofauna is being conducted and some preliminary results can be commented: one of the studied specimens is a fly belonging to Psychodidae: Sycoracinae, genus Sycorax. This genus has a world wide distribution, its record beginning in the Cretaceous amber of France. The fossil record of the genus indicates at least a Middle Cretaceous history previous to the isolation of the subcontinent. Another fly belongs to the Phoridae: Metopininae, genus Syneura. This genus had no fossil record and a Neotropical distribution with one species living also in the Nearctic. Syneura could then be a representative of an autochthonous stage of the South American entomofauna. The initial results are promissory to the better knowledge of the complexity of the insect Cenozoic biogeography of South America.