Structure and floristics of Cretaceous vegetation of southern Gondwana: implications for angiosperm biogeography

Abstract

A review of palaeobotanical/palynological data reveals that the vegetation of southern Gondwana was regionalised throughout the Cretaceous. Open forests of high productivity occurred in high southern latitudes whereas woodlands, heathlands and closed forests vegetated mid-latitudinal areas. Angiosperms first entered the region during Barremian-Aptian times from source areas in northern Gondwana. Early immigrants to the Australian-Antarctic assembly were of magnoliid stock, and migration routes involved southern South America. Early angiosperms in India also included non-magnoliid taxa which may have utilised an African/Madagascar corridor. Non-magnoliid angiosperms spread to the Austro-Antarctic landmass during the Albian, some 5-10 Ma after India was isolated from the southern Gondwanan assembly. For the remainder of the Cretaceous southern South America and the Antarctic Peninsula served as an exchange corridor for angiosperms between northern and southern Gondwana. This area was also the cradle of Nothofagus, whereas diametrically opposed land adjacent to the embryonic Southern Ocean was a differentiation centre for the Proteaceae. Angiosperm migration was step wise, and regulated by changing environmental circumstances associated with tectonic/volcanic activity and opening and enlargement of the southern oceans.