Naïveté, or the failure to recognise and respond appropriately and effectively to a novel alien predator, is thought to underpin Australia’s dubious record for the world’s worst rate of extinctions and declines in small to medium-sized mammalian fauna. We report on three years of research into predator naïveté in Australian native small-medium sized mammals. Australian native prey have an evolutionary history of marsupial predation, with the more recent addition of the placental dingo (Canis lupus dingo), which was introduced ~4000 years ago and is generally considered a native species. Placental foxes (Vulpes vulpes), dogs (Canis familiaris) and cats (Felis catus) were introduced around 150 years ago. We used behavioural analysis of remote-sensing camera footage to quantify recognition of predator odours by native Rattus fuscipes in the field, and surveyed Sydney, NSW, residents to quantify behavioural responses of native bandicoots (Isoodon macrourus and Perameles nasuta) to the presence of pet predators (cats and dogs) in back yards. Finally, we used analytical chemistry techniques to compare the chemical profiles of odour cues emitted by placental and marsupial predators. Naïveté in Australian fauna appears to be driven by significant chemical differences in the cues emitted by introduced placental and native marsupial carnivores. Native bush rats and bandicoots both recognised dog odours, which we attribute to thousands of years experience with the very closely related dingo. We present a wholistic picture of the current state of naïveté in Australian fauna, and discuss how it may have changed since placental carnivores were introduced.