A Lost Branch of Australia’s Marsupials Discovered: Meet the Keeunamorphia
Australia’s marsupials, kangaroos, koalas, wombats, Tasmanian devils, are among the most distinctive animals on Earth. For decades, paleontologists believed they all descended from a single ancestral lineage that diversified after Australia split from Antarctica roughly 35 million years ago. The fossil record told a relatively straightforward story.
It turns out that story was incomplete.
Researchers at the University of New South Wales have identified an entirely new order of Australian marsupials, the sixth known, from fossil teeth and jaw fragments discovered in the Riversleigh World Heritage Area in northern Queensland. Named Keeunamorphia, this lost lineage of small, insect-eating marsupials persisted for roughly 35 million years before vanishing around 15 million years ago.
“Not only is it a new order, it could also be the most ancient lineage of all Australian marsupials,” said Dr. Tim Churchill, a paleontologist at UNSW and lead author of the study published in the Journal of Paleontology.
Teeth That Tell a Story
The fossils that revealed the new order are modest in scale: isolated teeth and jaw fragments, each roughly the size of a grain of rice. But for paleontologists, teeth are exquisitely informative. Their shape, cusp pattern, and wear reveal what an animal ate, how it chewed, and where it fits on the tree of life.
Churchill and his colleagues analyzed three newly discovered species from the Riversleigh deposits, which were preserved in the remains of shallow cave pools. The specimens date to the Early Miocene, roughly 18 million years ago. The animals they belonged to were small, weighing between 25 and 200 grams, and likely lived in the wet rainforests that covered northern Australia at the time.
The critical clue came when the researchers compared the teeth to those of Djarthia murgonensis, a 55-million-year-old fossil from Queensland that is often considered a prototype for Australian marsupials. The resemblance was striking, suggesting that Keeunamorphia split off from the main marsupial lineage very early in evolutionary history and then remained largely unchanged for tens of millions of years.
“Whatever these things were, they seemed to be primitive compared to other marsupials at the time, and they seem to have been doing their own thing and surviving well enough alongside them,” Churchill said.
Rewriting Marsupial Evolution
Australia’s marsupial story now appears far more complex than a single ancestral line. The discovery of Keeunamorphia suggests that the continent was once home to multiple distinct lineages evolving in parallel, only one of which gave rise to the familiar modern groups.
“Evolutionary history is a lot more complex than just one group leading to all of Australia’s marsupials after being left behind when the continent broke off from Antarctica,” Churchill said.
The newly identified order fills a significant gap in the fossil record. There is a roughly 20-million-year gap in early Australian marsupial fossils, and paleontologists suspect many more undocumented lineages await discovery in that missing interval. The Riversleigh deposits, a UNESCO World Heritage site known for its exquisitely preserved fossils spanning the last 25 million years, continue to yield surprises.
The researchers combined detailed analysis of the fossil teeth with genetic data from living marsupial species, using Bayesian phylogenetic modeling to estimate when the lineages diverged. The analysis places Keeunamorphia as potentially the earliest branch of all Australian marsupial carnivores.
What Killed Them
The Keeunamorphia persisted for about 35 million years, a successful run by any measure. But around 14 million years ago, Australia’s climate began to shift. The continent cooled and dried, and the dense rainforests that covered much of northern Australia gave way to open woodlands. The small insect-eaters of Keeunamorphia, adapted to life in the wet forest understory, could not adapt.
Their extinction left no living descendants. But their teeth, preserved in limestone cave pools at Riversleigh, survive as a record of an evolutionary experiment that ran alongside the ancestors of today’s kangaroos and koalas for longer than most mammal lineages last.
Churchill suspects there are more discoveries to come. “Australia was swarming with primitive marsupial-like things during Gondwana times,” he said. Each new fossil tooth adds another piece to the puzzle, and another reminder that the evolutionary history of even well-studied continents still holds major surprises.
Sources
[1] University of New South Wales. “Scientists just discovered a lost branch of Australia’s marsupials.” ScienceDaily, 19 July 2026. https://www.sciencedaily.com/releases/2026/07/260715083546.htm
[2] Churchill, T.J., Archer, M., Hand, S.J., Beck, R.M.D. “A new metatherian order from Australia (Keeunamorphia, Metatheria), and new Early Miocene species from the Riversleigh World Heritage Area, northwestern Queensland.” Journal of Paleontology, 2026. DOI: 10.1017/jpa.2026.10238