Introduction

Prior to European settlement the Australian continental landmass (i.e. Australia plus the main island of New Guinea; Figure 10.1) was successfully invaded by only four groups of placental mammals: bats (Chapter 8), rodents, primates (our own species) and the dog (which almost certainly came with people; Chapter 19). Not surprisingly, bats were the earliest and in many respects, the most successful invaders (Hand 2006). Bats colonised Australia at least nine times, commencing sometime prior to the Early Eocene (Hand et al. 1994) when Australia was still connected to other Gondwanan landmasses. At the other end of the geological timescale, humans entered the region only during the late Pleistocene (c. 50 thousand years ago; kya) despite a much longer occupancy of islands to the immediate north (Morwood et al. 1999). Later still, the dog was transported to Australia around 4000 years ago (see Chapter 19). Rodents represent the middle ground in the history of placental invasion of Australia. They first entered the Australasian region during the late Miocene, after northward drift had brought the Australian continental plate into collisional contact with the Asian Plate (Lee et al. 1981). Despite the proximity of landmasses, the journey from Asia to Australasia still involved multiple water crossings, even during periods of low sea levels. Ultimately, only one of the many different kinds of rodents found in Asia proved fit for the challenge – the true rats and mice of the family Muridae – but members of this group succeeded on multiple occasions through natural dispersal and, more recently, with human assistance.

At the time of European settlement Australia supported around 66 species of native rats and mice, more species than in any family of marsupials or bats. Murine diversity is even more pronounced on the island of New Guinea and its major satellites to the north, with 114 species of native rodents already known and more being discovered (Helgen 2005a, b; Musser et al. 2008; Helgen and Helgen 2009; Musser and Lunde 2010). Native rodents thus comprised around 29% of the native terrestrial mammal fauna of Australia, and around 59% of that of the Melanesian islands. These figures do not rest comfortably with the common notion of Australasia as a continent of marsupials – but they do point to a fascinating history of invasion by what is clearly a highly successful evolutionary lineage.