However the Legislative Assembly's environment committee has recommended adopting both animals as the territory's mammal emblem, given the vote was so close.

More than 3500 people voted in a public poll to choose the mammal emblem, after it was revealed the ACT was the only state or territory without one.

The echidna, spotted tail quoll and little forest bat were all nominated as possible emblems, however the committee shortlisted the eastern bettong and the southern brush-tailed wallaby because both have been the subject of intensive conservation programs.

Eastern bettongs were reintroduced into the ACT in 2012 after being extinct on mainland Australia for about a century.

The tiny marsupial became an early favourite to take out the poll, thanks in part to the popularity of Brian Bettong.

Brian was rescued after being thrown out of his mother's pouch three years ago and has since become an ambassador for his species, with almost 2000 Twitter followers.

He became embroiled in a sassy tweet war with Triple J, who campaigned for Canberra electronic music duo Peking Duk to become the emblem.

That led to National Geographic contacting the Mulligans Flat sanctuary to write an article on the species.

However Mix 106.3 newsman David Sharaz became the unofficial cheerleader for the rock wallaby, which is one of Australia's most critically endangered animals.

It was last seen in the wild in 1959 and in 1996, Tidbinbilla Nature Reserve began a conservation program from a captive population of just three animals. There are now about 30 rock wallabies in the reserve.

Sharaz created a rival Twitter account, @rhonda_rocks  and impersonated ACT Parks and Conservation director Brett McNamara in a spoof video to spruik the wallaby.

Environment committee chair Suzanne Orr said the wallaby was ultimately chosen because it stood to gain the most from the increased publicity that would come with being the territory emblem, and because there was an established eastern bettong population in Tasmania.

However she said the committee wanted both animals to become the ACT's emblem, noting wryly it was a "very Canberran answer to what proved to be an incredibly difficult question".

"As a resident of Mulligans Flat, the eastern bettong has become synonymous with the northside of Canberra. The southern brush tailed rock wallaby on the other had is clearly a southsider happily hopping around the Tidbinbilla nature reserve," Ms Orr said.

"The eastern bettong having been reintroduced from Tasmania is illustrative of everyone who has moved from somewhere else who now calls Canberra home. The rock wallaby on the other hand as documented through Indigenous rock art has a long association with the region.

"The rock wallaby demonstrates the amazing conservation work  that's going on in Canberra while the bettong highlights how important restoring our biodiversity is. These efforts to preserve the mammals both show an equally important part of the ACT's commitment to our environment."

While Brian Bettong's handler and Mulligan's Flat ecologist Dr Kate Grarock tweeted that the dual emblem would be "cool" and an "Australian-first", others aren't pleased the committee chose to sit on the fence.

"While it’s nice the ACT government wants to give a participation award to Brian, what would be the point of the poll if they were going to make both the emblem all along?" Sharaz said.

"When Malcolm Turnbull won the election in a narrow victory, did we give Bill Shorten the keys to the lodge too because he gave it a go? I’ll be outraged if the Assembly decided to go against the will of the people."

University of Canberra invasive species expert Dr Mike Braysher also criticised the committee for shortlisting the bettong and rock wallaby as both species were unlikely to survive reintroduction to the wild.

"If one of these two are chosen, the result will be a mammal emblem that only exists in captivity or one that has to be continually released in an attempt to re-establish it and at great ongoing cost to manage native and non-native predators," he said in his submission.

"We will end up like Victoria with their bird emblem the helmeted honey eater, or which is better known amongst scientists as the helmeted money eater. It is only still in Victoria through a long-term breeding program at Melbourne Zoo and continual release to the wild where they soon die out."

Dr Braysher said it would be better to choose a mammal with good long term prospects like the echidna or the swamp wallaby.

However the committee said they prioritised prioritised biodiversity and conservation when deciding the emblem shortlist.

Woodlands and Wetlands Trust president Alison Russell-French said the process had been "extremely positive" for the "hidden" native animals that are disappearing.

"Australia has the worst mammal extinction rate in the world. We have 16 mammals rarer than the
giant panda. To help people fall in love with endangered animals is crucial if we are going to save
them," Ms Russell-French said.

“We are not looking forward to breaking the news to Brian, but politics is a hard game, and Rhonda ran a strong campaign for her species. We hope she is ready and committed for her life of advocacy, and we look forward to sharing that responsibility."

Ms Orr said the adoption of a mammal emblem could also lead to the design of a coat of arms for the ACT, and a possible redesign of the territory's official flag.