Standing around three feet high, the modern koala is roughly 25 pounds of claws and teeth, tufty ears and fluffy white marsupial tummy. You could give one a hug — experts suggest that they prefer it if you don’t — but you wouldn’t want to carry it around all day.
Now imagine that same koala, or one quite like it, weighing in at a much more manageable (and potentially cuter) six pounds.
Researchers at Flinders University in Adelaide, Australia, believe that such a creature, named Lumakoala blackae, once made its home in the country’s Northern Territory some 25 million years ago, most likely spending its days snacking on soft leaves and the occasional insect.
Their research, based on the discovery of fossilized molars at the Pwerte Marnte Marnte fossil site in the Australian outback, was published in the journal Scientific Reports this month.
Marsupials are often erroneously thought to live only in Australia. While Australia does have an impressive array of particularly charismatic examples — platypuses, Tasmanian devils, kangaroos, koalas, wombats, wallabies and bandicoots, to name a few — these comprise roughly 70 percent of the world’s population, with the other 30 percent hailing from the Americas.
Somewhere between 65 million and 50 million years ago, Australian marsupials, known as diprotodontians, set off on a different evolutionary track from those located elsewhere in the world. The details of precisely how this occurred are unclear: There is, researchers note, an “approximately 30-million-year-gap” in the fossil record obscuring the first half of diprotodontian evolution, tens of millions of years ago, when the world’s continental boundaries were entirely different than today’s.
This unprepossessing cat-sized koala may be the missing link, Arthur Crichton, a doctoral student at Flinders University who led the study, said in a statement.
“In the past, it was suggested the enigmatic Thylacotinga and Chulpasia” — two other species of ancient marsupials — “may have been closely related to marsupials from South America,” he said.
“However, the discovery of Lumakoala suggests that Thylacotinga and Chulpasia could actually be early relatives of Australian herbivorous marsupials such as koalas, wombats, kangaroos and possums.”
Fossilized remains found at the site near Alice Springs had previously been thought to resemble some of those specimens previously found in South America, said Robin Beck, who coauthored the study with Mr. Crichton.
Instead, Dr. Beck said, also in a statement, “These Tingamarran marsupials are less mysterious than we thought, and now appear to be ancient relatives of younger, more familiar groups like koalas.” Tingamarra is an extinct genus of small mammals from Australia.
He added: “It shows how finding new fossils like Lumakoala, even if only a few teeth, can revolutionize our understanding of the history of life on Earth.”
In fact, koalas of all sizes seem to have proliferated in prehistoric Australia, Gavin Prideaux, a Flinders University paleontologist and a co-author of the study, said in a statement.
“Until now, there’s been no record of koalas ever being in the Northern Territory; now there are three different species from a single fossil site,” Dr. Prideaux said. “While we have only one koala species today, we now know there were at least seven from the late Oligocene — along with giant koala-like marsupials called ilariids,” he said, referring to a period about 30 million years ago.
The littlest koalas are particularly appealing. But their largest relatives, the ilariids, might have been a rather terrifying proposition, with an estimated weight of as much as 440 pounds, roughly the size of an upright piano.