Camptonectes and Plicatula (Bivalvia, Pteriomorphia) from the Upper Maastrichtian of northern Patagonia: palaeobiogeographic implications

Maastrichtian shallow marine strata in the Southern Hemisphere yield a characteristic cool-water molluscan fauna, used to define the Weddellian Province. These short-lived molluscan assemblages started to disintegrate during the final phase in Gondwana breakup (Cretaceous/Paleogene); however, some of its elements persisted well into the Cenozoic and are even found in extant faunas of circum-Antarctic shelf regions. In southern South America, the Weddellian Province reached as far north as the Neuquén Basin (west-central Argentina), where numerous austral taxa are known from marine Cretaceous and Paleocene rocks. However, some of these taxa show no austral affinities at all, and appear more closely related to northerly groups then living in relatively warm waters. This explains the mixed character of the Neuquén Basin fauna, particularly in the latest Cretaceous. Two species of warm-water bivalves from the Late Maastrichtian Jagüel and Roca formations in northern Patagonia, Plicatula georgiana Fritzsche, 1919 and Camptonectes tutorae sp. nov., provide additional evidence for this mixed character, and reflect the influence of higher temperatures spreading south. These two taxa are here compared with similar species from Upper Cretaceous (and younger) rocks in other parts of the world, and their palaeobiogeographic affinities are discussed. The issue of global sea warming recorded during the latest Maastrichtian is also addressed.