Oysters are amongst the most frequent and characteristic fossils in the sedimentary marine sequences of the Patagonian Mesozoic and Cenozoic. They were particularly diverse and abundant during the Late Cretaceous-Paleogene transition in the Neuquén Basin, where they appear in vast accumulations throughout several lithostratigraphic units. Many nominal species have been described since these rocks were first described during the second half of the nineteenth Century. The great majority of these species were -unfortunately- based on only a limited number of specimens, in many cases with inadequate stratigraphic information. This naturally rendered their use as biostratigraphic tools almost valueless, although a number of authors did in fact base stratigraphic divisions on their presence/absence in certain horizons. However, as a comprehensive taxonomic revision of the taxa involved was missing, such divisions based solely on oyster content could not hold fast or either did so very weakly. This situation -for the Neuquén Basin- was remedied in part by Casadío (1998), who studied large collections and revised most types, setting the foundations for an in depth revision of all oysters in the Maastrichtian-Cenozoic of Patagonia. The large data set available to him allowed a sound biostratigraphic scheme, proving the potential usefulness of this group of bivalves for regional correlation within the southern portion of South America.
In this paper we describe three species of oysters -two of them are new- collected in rocks referred to the Maastrichtian-Danian Jagüel and Roca Formations in the Neuquén Basin. One of these species ( Cubitostrea primordialis n. sp.) was collected in Maastrichtian beds of the Jagüel Formation, being the oldest record of this genus. The other two are Turkostrea damboreneae nom. nov. [= Turkostrea mendozana (Fritzsche, 1919), p. 361], from the Maastrichtian Jagüel Formation and from the Maastrichtian beds of the Roca Formation, and Turkostrea argentina n. sp. from the Danian part of the Roca Formation. All three species suggest a probable austral origin for the Tribe Turkostreini.
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