Determining the relative roles of dispersal and vicariance in the assembly of the New Zealand fauna. New fossils from New Zealand's St Bathans Fauna (19-16 million years) will revolutionise our understanding of the shared biodiversity and evolutionary history of New Zealand and Australia through the first views of the origin and evolution of major Gondwanan groups including frogs, crocodiles, birds and bats on the now mostly-drowned continent Zealandia.