It is also closely related to the last surviving species of marsupial lion, Thylacoleo carnifex, which had enormous dagger-like fangs and the strongest bite of any known mammal species.
Though that species survived until around 30,000 years ago, it is thought that the arrival of humans in Australia may be linked to its demise.
This new lion is considerably more ancient. The scientists who discovered it estimate that it has been extinct for at least 19 million years.
It is also considerably smaller. While at 130 kg the larger marsupial lions could have been a real threat to our ancestors, this new species is around the size of a dog, weighing around 23 kg.
The discovery has helped researchers understand the family tree of marsupial lions, which are thought to have existed in Australia at least as far back as 25 million years ago.
"The identification of these new species have brought to light a level of marsupial lion diversity that was quite unexpected and suggest even deeper origins for the family," said at Dr Anna Gillespie, a palaeontologist at the University of New South Wales and lead author of the Journal of Systematic Palaeontology paper describing the new species.
By examining the teeth of the newly identified specimen, Dr Gillespie and her collaborators have deduced that it is one of the most primitive marsupial lions discovered so far.
Marsupial lions are thought to have been skilful ambush predators that would have terrorised the Australian bush.
Prior to the arrival of humans in Australia, the continent was home to a huge array of giant marsupials.
The hunting activities of humans, together with changes in the Australian climate, have been blamed for the extinction of many of these creatures.
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