With its fox's face, tiger's stripes, kangaroo's pouch and exclusive existence on a small island, the Tasmanian tiger was a weird creature.

Now, by sequencing the tiger's DNA for the first time, Melbourne scientists have proven it was like nothing else dead or alive. It turns out its closest relatives in physical appearance are foxes or wolves - but it was a marsupial, and one of its closest genetic relatives is a wallaby.

"It looks nothing like any other marsupial. It's a dog with a pouch," says University of Melbourne Associate Professor Andrew Pask, who led the international team behind the work.

Associate Professor Pask has always been fascinated by marsupials –  a class of creatures with pouches that are mostly unique to Australia and weird enough in their own right – and particularly with how evolution threw up an oddity like the Tasmanian tiger.

For years, he dreamed of sequencing the tiger's DNA, but the research community believed it was an impossible task. The tiger went extinct in 1936, when the science of animal preservation was in its infancy. All the specimens the research team could find had been so poorly preserved their DNA has degraded into fragments.

"It was like trying to piece together a 10-million piece jigsaw," Associate Professor Pask says.

That was until they came on a tiny jar, stored deep within the Melbourne Museum's vast specimen stores.

Inside floated an infant tiger, barely big enough to leave its mother's pouch. By fluke 108 years ago someone had dropped it into a jar of ethanol - an uncommon preserving liquid at the time - which had perfectly protected its DNA.

What Associate Professor Pask's team found when they peered into the chromosomes was remarkable enough to merit publication in Tuesday's edition of journal Nature Ecology & Evolution.

"It turns out tigers are the single best example of convergent evolution – when two animals that are not closely related evolve to look the same – that has ever been described in the literature. Which is really astounding," says Associate Professor Pask.

Tasmanian tigers' closest genetic relatives are wallabies, the research found. But tigers don't look anything like them, says Museums Victoria's Dr Christy Hipsley, who was also part of the team. 

Wallabies and tigers both evolved from a common ancestor millions of years ago. But while the wallaby evolved to become an effective plant muncher, the tiger became a predator.

Natural selection took that same DNA the wallaby shares and moulded the tiger into the most efficient predator it could. And if you want to hunt small animals, the most efficient shape you can take on is that of a fox or wolf. 

That explains why the skulls of Tasmanian tigers and common red foxes are almost identical, despite their very different DNA, says Dr Hipsley. It also explains the tiger's odd collection of traits: a mix of wallaby DNA and predatory adaptions.

Dr Mark Eldridge, a marsupial expert with the Australian Museum Research Institute who was not involved in the study, suggests that when Tasmanian tigers evolved, there was no apex predator in Australia.

The tiger essentially evolved to fill a gap in the market.

"What the thylacine has done is fill that niche of an apex predator like a wolf or a fox, preying on other large vertebrates. So it would seem that evolutionarily, there's a certain suite of adaptations that you have to have to succeed at that. Teeth for grabbing hold of prey and slicing up meat. It's built for chasing."