The Terrestrial Biotic Dimension of West Antarctica (WANT)

Abstract

The Late Cretaceous terrestrial biota from Antarctica come from the marine sediments of the James Ross Basin and the western flank of the Antarctic Peninsula. A compilation of data for Cretaceous and Paleogene Antarctic floras from these areas provides different perspective on floristic and vegetation change when compared with those coeval floras from southern South America.The Paleogene sequence in southern South America (Patagonia) and the Antarctic Peninsula reveals floristically distinct periods (late Paleocene, early and middle Eocene and latest Eocene), based largely on leaf assemblages. The La Meseta paleoflora is distinctive in having a predominance of Antarctic taxa especially Nothofagus, podocarps, and araucarian conifers in the Eocene deciduous and evergreen forests. This suggests a cooling trend during the Eocene of Antarctica with mid- to late Eocene seasonal, cool-temperate, rainy climates and latitudinal and altitudinal gradients. In the Late Cretaceous of James Ross Basin at least nine taxa of non-avian dinosaurs (a megalosaur-like theropod, a nodosaurid ankylosaur, a dromaeosaurid theropod, an iguanodontid, a hypsilophodontid, and a large-bodied lithostrotian titanosaur) and at least four avian dinosaurs have been reported or described from the Campanian/Maastrichtian deposits of this basin. Additional non-avian dinosaur evidence from the same area is based upon the occurrence of Maastrichtian sauropod? footprints of Snow Hill Island. In the Paleogene, of the six allomembers of the La Meseta Formation, only three, Acantilados (Ypresian), Cucullaea I (Ypresian/Lutetian) and Submeseta (Priabonian), contain endemic terrestrial mammals (metatherians and meridiungulates) and birds. Seafloor spreading between Antarctic Peninsula (West Antarctica) and South America possibly opened an intermittent seaway by the end of the Paleocene (Thanetian, 55 Ma) but subsequent tectonic and sedimentary events may have delayed the final break up between the two continents until the end of the Late Eocene (Priabonian, 34 Ma) with the opening of the Drake Passage.