Late Cainozoic rainforest vertebrates from Australopapua: evolution, biogeography and extinction

Abstract

Understanding the evolution, biogeography and extinction of Australopapuan vertebrate lineages is fundamental to determining baseline responses of those groups to past environmental change. In light of predicted climatic change and anthropogenic impact, it is imperative to determine the trajectories of Australia‟s modern flora and fauna. In particular, mesothermic rainforest faunas are among Australia‟s most vulnerable terrestrial biota under threat from both natural and anthropogenic causes. There is a gap in knowledge of past patterns of change and, in particular, a conspicuous lack of direct evidence of response of rainforest faunas to past climatic change. This study documents the late Cainozoic Australopapuan rainforest vertebrate record and its response to environmental change via adaptive radiation, biogeographical change and extinction. In particular, it provides the first detailed systematic appraisal of Quaternary fossil sites and local faunas from northern Australia. The study documents the only known Quaternary mesothermic rainforest fauna in Australia and its transition to a xeric-adapted fauna during the middle Pleistocene. The fossil assemblages analysed are comprised of dozens of species, including several new genera and species. Each fossil taxon shares a close phylogenetic relationship with others either known only from the Australian Tertiary record or from Quaternary-Recent New Guinea and Wet Tropics rainforests. The presence of many species is evidence of previously much larger distributions followed by subsequent massive range retractions. Detailed documentation of this rare fauna testifies to rainforest stability in central eastern Queensland until approximately 280,000 years ago, when the development of an El Nino dominated climate generated variable climatic patterns that could not support aeseasonal rainforest. Extinction of this late Pleistocene rainforest fauna serves as one of only two examples of major rainforest faunal turnover in Cainozoic Australia, the other occurring in the late Miocene. These two major extinction events are compared. The late Pleistocene faunal extinction differs from the late Miocene event in being biased towards large-bodied, terrestrial herbivores and carnivores (both reptile and mammal). This study also combines fossil and phylogenetic data with latest understanding of palaeogeography, tectonics and sea level history along Australia‟s northern margin to provide hypotheses of faunal dispersal between New Guinea and mainland Australia throughout the Neogene.