CANBERRA: Mountain formation in New Guinea five million years ago triggered the spread of diverse rodents across Oceania, Australian research has found.

In a study published in Current Biology recently, researchers from the Australian National University mapped the DNA of more than 150 rodent species from across Australia, New Guinea and Melanesian islands to discover how they are related and how they spread across the Pacific.

They found the formation of mountains approximately five million years ago was the major driver in their proliferation by increasing connectivity with Australia, Solomon Islands and Maluku Islands.

"We've known for some time that Australia's native rodents originated in Asia and arrived in our region via water — possibly a single pregnant animal floating across on a piece of driftwood. Now we have an accurate timeline for this, and an explanation for why we see so many species today," Emily Roycroft, lead author of the study, said in a media release.

"Our study shows native rodents are exceptional at colonizing new areas. When they first arrived in Australia they adapted to a lot of new environments — including the arid desert."

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Until now little was known about the evolution of more than 150 rodent species found only in Australia and New Guinea, including the rakali or "water rat" — a semiaquatic nocturnal rat that can be seen swimming around Canberra's lake.

Roycroft's team used a new approach to gather DNA from museum specimens of extinct and elusive species dating back 180 years.

She said having extra information about the rodents could be vital to their future survival.

"Native rodents have a deep intrinsic value in our ecosystems. They're ecosystem engineers; they aerate soil via burrowing and foraging and they help to disperse seeds and fungal spores," she said.

"But they also have the highest extinction rate of any Australian mammal group, due to extreme habitat loss and introduced predators. If we lose even one native species, it can throw off the balance in an ecosystem."

She said understanding how native rodents evolved and adapted will help people conserve those that have been left.