Southern polar forests: The Early Cretaceous floras of Victoria and their palaeoclimatic significance

Abstract

A diverse fossil flora, including cryptogams, pteridosperms, Cycadales, Bennettitales, Ginkgoales, Coniferales and angiosperms, occurs in Early Cretaceous fluvial and lacustrine strata in the Otway and Gippsland basins in southern Victoria. Both evergreens (e.g. araucarians, cycads, ferns) and deciduous or semi-deciduous forms (e.g. certain pteridosperms and Ginkgoalès) seem to have been represented. Certain ferns, ginkgos and conifers grew to a large size. Overall, the assemblages are typical of Early Cretaceous floras. The associated fauna includes dinosaurs (hypsilophodontids, allosaurs), lepidosaurs?, chelonians, birds, fish (including the lungfish Ceratodus), and insects. The evidence of the biota as a whole suggests a warm- to cool-temperate, relatively equable climate of moderate seasonality with no widespread winter freezing. The complex Mesozoic apparent polar wander path (APW) indicated for Australia places Victoria in high to polar palaeolatitudes (ca. 70–85°S) during the Early Cretaceous. This APW path is supported by paths for other Gondwana continents. The existence of the Victorian Early Cretaceous forest and biotic communities through polar nights of about two to five months' duration is difficult to accept. Evergreen species would have required relative equability of light, whatever the temperature, the dinosaurs foliage throughout the year, and the lungfish warm to temperate conditions without freezing. In view of the consistency of Mesozoic palaeomagnetic results for Gondwanaland and the enigmatic presence of Mesozoic and early Cenozoic fossil floras and faunas in very high northern palaeolatitudes, the possibility of a reduced obliquity of the ecliptic in Mesozoic—early Cenozoic time should be considered.