Patterns of vegetational change through the Late Mesozoic in southern Gondwana

Abstract

Near the close of the Triassic the Dicroidum flora of Gondwanan regions underwent considerable modification involving replacement of several corystosperms, podocarp conifers and seed ferns (eg., Dicrodium, Linguifolium, Heidiphyllum) by newly evolved taxa of the Bennittitales, Caytoniales, and cheirolepidacean conifers. Floral turnover was accompanied by profound faunal modifications that included proliferation of dinosaurs and turnover of invertebrate taxa in the marine realm. The macrofloral and palynofloral record reveals that the Gondwanan Early Jurassic flora reflects a more cosmopolitan aspect than that of the Triassic, but the Gondwanan character was retained by several notable endemics (eg. pentoxylaleans, araucarians). Moreover, the fossil plant record implies that there was floral regionalism between peripheral (South America, eastern Australia) and inland (Western Australia, eastern Antarctica, India, Madagascar) areas of Gondwana. Regionalism within the vegetation of southern Gondwana became more pronounced during the Middle and Late Jurassic and accelerated during the Cretaceous when angiosperms entered mid-high southern latitudes. By the close of the Cretaceous southern Gondwanan vegetation was strongly regionalised not only across the latitudes, but also within the same latitudinal belt. Causative mechanisms appear to be related to environmental and climatic perturbations resulting from volcanic and tectonic activity concurrent with rifting, drifting, and opening of oceans. Patterns of vegetational change and of strengthening floral regionalism through the Late Mesozoic in southern mid-high latitudes are discussed with reference to progressive fragmentation of the Gondwanan assembly