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A rare mammal has been discovered living in Western Australia (WA) decades after it was thought to have been wiped out of the region.

The distinctive black-footed tree rat was spotted by chance last year on a seasonal monitoring trip when a researcher went on night time stroll.

Months of camera footage have now confirmed its existence.

Researchers said they "cracked a bottle of champagne" to celebrate its return after a 30 year absence.

The native rat has telltale black feet and a long black and white tail.

Weighing up to 800g, it's considered enormous compared to its more common relatives such as the golden-backed tree-rat at around 200g.

The rat can be found in the Northern Territory but was last seen in the Kimberley area of WA in 1987.

It was believed to have been wiped out by bushfires, predatory cats and human activity.

WA's state's biodiversity and conservation department said it was an amazing occurrence given the decline in small mammal numbers in the northern regions of the state.

"If you haven't seen an animal in 50 years you can start to make a case that it can be made extinct. We won't need to do that now," Department of Biodiversity, Conservation and Attractions ecologist Ian Radford told the ³ÉÈË¿ìÊÖ.

"We're all very excited... some of us cracked a bottle of champagne when we heard the news.

"There's a been a major programme to improve the fire regime for a number of years now, so this is sort of like the icing on the cake."

Population estimates remain uncertain, with Mr Radford saying that because they had been so elusive they were very difficult to track.

Tree-rat species survive in stringy bark forests in northern Australia and prefer lots of shrub layer and fruiting trees.

The rugged north of Kimberley is recognised as a stronghold for species that are now extinct across the northern regions of Australia.