Quite often, this has happened via over-water colonisation. In our region alone rodents have transitioned between different geographic areas or islands at least 24 independent times in the past 5 million years. Over the past few million years, they also have spread across the Solomon and Maluku Island archipelagos. Native rodents first arrived to New Guinea from Asia 8.5 million years ago, and then arrived to Australia 5 million years ago. In the last few million years, rodents have been especially mobile – repeatedly moving between New Guinea, Australia and neighbouring island archipelagos, generating many new species in the process. In Australia, they have adapted to many new environments including the harsh arid desert. Rodent ancestors first arrived from New Guinea into Australia around 5 million years ago, probably via a land bridge exposed during a period of low sea level. This expansion opened new environments for rodents to adapt to, and increased connectivity between New Guinea, Australia, and neighbouring islands. Tectonic activity triggered the uplift of an impressive mountain range through the centre of New Guinea, and led to the formation of expansive lowlands. This adorable mouse was considered extinct for over 100 years - until we found it hiding in plain sightĪround 5 million years ago, New Guinea experienced a big geological change. But they then stayed put for 3.5 million years. Our results show the earliest arriving rodent ancestors, probably tropical forest specialists, initially spread across this earlier New Guinea. In contrast to the large and high-elevation island of modern New Guinea, 8.5 million years ago it was likely made up of a series of smaller, disconnected islands. Both New Guinea and Australia looked very different back then. Our research dates this event to around 8.5 million years ago. There’s never been a land connection between Asia and New Guinea, and so we know this must happened via over-water colonisation – possibly on a piece of driftwood. The genetic relatedness of distant rodent relatives tells us the ancestor of Australia’s native rodents originated in southeast Asia. Trustees of the Natural History Museum London/C. This is a specimen of Gould’s mouse from the Natural History Museum in London. Many surviving native rodents remain at serious risk of extinction, with urgent conservation action needed to secure their future. Native rodents have also suffered the highest rate of recent extinction of any mammal group in Australia, with 11 mainland species declared extinct since European colonisation in 1788. Our new research unites genomic sequencing and museum collections to reconstruct the evolutionary tale of native rodents, including many extinct and elusive species – and they have a fascinating origin story. Until now, we’ve had an incomplete picture of how there came to be so many species. These include the rakali, an otter-like rodent with webbed feet, and desert hopping mice that get around like tiny kangaroos. When you count their close relatives across New Guinea and island neighbours, there are over 150 species. Today, Australia has more than 60 species of native rodents found nowhere else in the world. A single, pregnant rodent floating on driftwood across the treacherous waters between Asia and New Guinea 8.5 million years ago may be behind the eventual colonisation of native rodents in Australia, our new research suggests.
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