Camptonectes and Plicatula (Bivalvia, Pteriomorphia) from the Upper Maastrichtian of northern Patagonia: palaeobiogeographic implications S. Casadı´o * , M. Griffin, A. Parras Universidad Nacional de La Pampa, Uruguay 151, 6300 Santa Rosa, La Pampa, Argentina Received 29 July 2004; accepted in revised form 11 January 2005 Available online 16 September 2005 Abstract 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 Neuque´n 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 Neuque´n Basin fauna, particularly in the latest Cretaceous. Two species of warm-water bivalves from the Late Maastrichtian Jagu¨el 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. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Bivalvia; Plicatula; Camptonectes; Palaeobiogeography; Taxonomy; Maastrichtian; Patagonia; Argentina 1. Introduction Relatively shallow seas separated Australia, New Zealand, Antarctica and South America during the Late Cretaceous and Early Paleogene (Zinsmeister, 1982), thus enabling the persistence of a certain degree of similarity in marine molluscan faunal composition in these areas. This similarity originated prior to the final fragmentation of Gondwana during the Early Paleogene, and has been noted by numerous authors (von Ihering, 1907; Steinmann and Wilckens, 1908; Wilckens, 1910, 1911, 1922, 1924; Finlay and Marwick, 1937; Howarth, 1966; Henderson, 1970; Zinsmeister, 1976, 1977, 1979, 1982; Freneix and Grant-Mackie, 1978; Freneix, 1981; Woodburne and Zinsmeister, 1984; Macellari, 1985, 1987; Griffin, 1991; Pascual et al., 1992; Griffin and Hu¨nicken, 1994; Stilwell, 1994, 1997, 1998, 2000, 2003; Zinsmeister and Griffin, 1995; Henderson et al., 2000). To characterise taxa that appeared in this region prior to the Paleogene, Fleming (1963) proposed the term ‘‘palaeoaustral’’. Subsequently, Kauffman (1973) introduced the Austral Province, as based on Cretaceous bivalve distribution. This province includes the southernmost tip of South America and the easterly * Corresponding author. E-mail address: scasadio@cpenet.com.ar (S. Casadı´o). 0195-6671/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.cretres.2005.01.009 www.elsevier.com/locate/CretRes Cretaceous Research 26 (2005) 507e524