Reappraisal of the fossil record of Polycotylidae (Sauropterygia: Plesiosauria) from the Upper Cretaceous of Chile

Abstract

The polycotylids, mostly short-necked plesiosaurs, were a clade of marine reptiles with an almost cosmopolitan geographical distribution in the Cretaceous Period. In austral continents, like South America, Antarctica and Australia, the presence of this group has remained relatively poorly documented, where apart from some rare specimens, most records are limited to fragmentary material. Reports of this group from South America are infrequent, particularly from Chile. Therefore, a critical review of the fossil record of Upper Cretaceous polycotylids from Chile is presented here. Previous putative reports of the group from the Quiriquina Formation (upper Maastrichtian) of the Arauco Basin (central Chile) were exclusively supported by misidentified axial elements belonging to elasmosaurid plesiosaurs, and are thus dismissed here. On the contrary, the presence of Polycotylidae in upper Campanian-lower Maastrichtian levels of the Dorotea Formation, in the Magallanes Basin (southern Chile), is confirmed. The pattern of taxonomic diversity, including polycotylids together with abundant, mostly non-aristonectine elasmosaurs in uppermost Cretaceous rocks of the Magallanes Basin, is similar to that observed in coeval localities of Argentinean Patagonia and Antarctica, but different from that observed in the Quiriquina Formation and the upper levels of the Dorotea Formation, where aristonectine elasmosaurids dominate the plesiosaur fauna. Polycotylids of equivalent age have also been described in other regions of the Weddellian Province, such as New Zealand. Polycotylidae seem to disappear from the fossil record during the late Maastrichtian in high southern latitudes of former Gondwana territories.