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

CASADÍO, S.; GRIFFIN, M.Y PARRAS, A.

CRETACEOUS RESEARCH (PRINT)

Año: 2005 p. 507 - 524

0195-6671

Shallow seas distributed around the southern continents during the Maastrichtian carry a characteristic cool-water molluscan fauna used to define the Weddellian Province. This short-lived molluscan fauna began disintegrating during the final phase of the dismemberment of Gondwana during the Cretaceous/Paleocene, but some of its elements persisted well into the Cenozoic and can even be recognized in modern faunas living in shelf areas in the circumantarctic regions. In souther South America, this province reached as far North as the Neuquén Basin in west-central Argentina, where many austral taxa can be recognized in the Cretaceous and Paleocene marine rocks exposed there. However, some of the taxa contained in these rocks show no  austral affinities at all. In fact, they appear to be more closely related to northern groups living then in relatively warmer waters. This renders a mixed character to the Neuquén Basin fauna, particularly at the close of the Cretaceous. Two species of warm-water bivalves occurring in the late Maastrichtian Jagüel and Roca formations in northern Patagonia provide additional confirmation that this mixed character of the fauna in the region during that time. This reflects the influence of warmer temperatures – in the shallow water – spreading southwards and thus stretching the geographic range of the typically northern taxa.. The two bivalve species, i.e., Plicatula georgiana Fritzsche, 1919, and  Camptonectes tutorae n. sp. are described and adequately illustrated. Comparison with similar taxa from Maastrichtian rocks in other parts of the world provide insight into their paleobiogeographic affinities, which are amply discussed. Their arrival in the region as a consequence of the global shallow sea warming recorded during late Maastrichtian is addressed.