South America

For more than 60 million years South America was isolated from its gondwanan neighbors, its biota evolving in what paleontologist G. G. Simpson called "a splendid isolation." Approximately 3.5 million years ago a profound event occurred that integrated faunas from North and South America: the Panamanian Land Bridge closed. This "Great American Interchange" and the earlier Cenozoic history of South America's fauna have largely been unraveled by the study of fossil mammals (e.g., Simpson, 1948). Unlike fossil mammals, Cenozoic insects from South America are scarce, with only four Cenozoic formations yielding significant numbers of insects, plus several smaller formations. Petrulevicius and Martins-Neto (2000) catalogued 73 named Cenozoic insects in 11 orders, not including diverse fossil nests and burrows from southern South America.

The first intensively studied formation is the Margas Verdes Formation from Sunchal, Jujuy Province, Argentina. Petrulevicius and Martins-Neto (2000) refer to this as the Maiz Gordo Formation, Late Paleocene (ca. 60 myo). T. D. A. Cockerell published various papers on this formation (e.g., Cockerell, 1936), in which he described diverse beetles (of putative Carabidae and Curculionidae), as well as Orthoptera, Dermaptera, and Auchenorrhyncha, based on elytra and tegmina.

Probably the most diverse and significant formation is the Tremembe Formation (Oligocene), from Taubate Basin, Sao Paul state, Brazil. Thus far, it contains six orders, the most significant being several rare Lepidoptera. These include two butterflies, Archaeolycorea ferreirai (Nymphalidae: Danainae) and Neorinella garciae (Satyrinae), and a noctuid moth, Philodarchia cigana. Other smaller Cenozoic deposits are the Pirassununga Formation (Oligocene) of Sao Paulo, Brazil, and the Fonseca Formation of Minais Gerais, Brazil. The latter has yielded the mastotermitid termite Spargotermes limai. A. E. Emerson, who described the termite, attributed the Fonseca Formation to the Eocene, but Petrulevicius and Martins-Neto (2000) indentify it as Oligocene. The Ventana

Formation (Paleocene-Eocene) of PichileufĂș, RĂ­o Negro Province, has yielded several ants. The Early Eocene "Tufolitos Laguna del Hunco" deposit of Chubut, patagonian Argentina is a caldera lake deposit preserved with leaves, insects, and caddisfly cases. The cases are composed of bits of plant material, not sand grains or pebbles (Genise and Petrulevicius, 2001).

A fascinating formation is the Palacio Member of the Ascencio Formation (latest Cretaceous-earliest Paleocene), Uruguay, which contains abundant and diverse burrows and nests in paleosols. The ichnofossils were first studied by Frenguelli (1939), now mostly by Genise (1999; Genise and Bown, 1994; Genise and Laza, 1998). The burrows were formed by scarabeids and by some unidentified insects; most significantly there appear to be burrows from perhaps 10 species of bees. Identification of particular groups of bees (e.g., Halictinae) is based on nest architecture, which can be distinctive for certain groups. Bee fossils are scarce, and these would be among the oldest ones known.

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