Abstract
During the Late Campanian‐Danian interval the South Atlantic Ocean invaded a large part of Patagonia in different events making an archipelago. Plesiosaurs from northern Patagonia of Late Campanian‐Early Maastrichtian age were found in the Allen Formation. The sedimentology and faunal content, mainly at the Pellegrini Lake, suggest marginal marine environments, such as coastal plains, lagoons or estuaries. Toward the end of the Maastrichtian a new relative sea‐level rise occurred, and the plesiosaurs are recorded in sediments of deeper marine environments of inner or middle platform.
As pelagic reptiles, plesiosaurs had the potential capacity of worldwide distribution. Polycotylids and elasmosaurids have been found in northern Patagonia. There are at least two morphotypes (here determined as Elasmosauridae gen. et sp. indet. and Plesiosauroidea gen. et sp. indet.) which are also recorded in the south of the Eastern Pacific (Chile). Another plesiosaur found in central Patagonia, Aristonectes, with controversial phylogenetic relationships, suggests that some of them inhabited southwestern Gondwana (Argentina, Chile and the Antarctic Peninsula). Whether any of these taxa of northwestern Patagonia reached a south gondwanan distribution, is still controversial. However, at least in New Zealand there are plesiosaurs with similar characteristics, particularly in the limbs, to those found in plesiosaurs from Patagonia and Chile; hence, this hypothesis should not be discarded. Evidences of south Gondwanan distribution in other pelagic reptiles such as mosasaurs have been reported. Copyright © 2007 John Wiley & Sons, Ltd.