Artist's impression of _Protemnodon tumbuna_ from Nombe Rockshelter. Peter SchoutenRoughly 50,000 years ago, a kangaroo unlike any alive today lived in the mountain rainforests of New Guinea. First discovered by Western science in 1983, Protemnodon tumbuna was roughly the size of a modern red kangaroo but much more stocky and muscular. Most peculiarly, it hopped little, if at all. It moved mostly on all fours, with long, strong forelimbs providing support for agile bounding through complex and steep terrain.This strange animal was one of many megafauna that once roamed Australia and New Guinea. It is thought to have gone extinct some 20,000 to 50,000 years ago. However, our new study, published in the journal npj Biodiversity, suggests Protemnodon tumbuna survived until as late as 6,000 years ago in northern New Guinea. This constitutes solid evidence the Australian and New Guinean megafauna did not all go extinct at the same time, but that some hung on for much longer than others. It also contributes to a more complex image than conventional arguments about what drove the extinction of megafauna.Clues from Papua New GuineaAll seven Protemnodon species had gone extinct in Australia by 41,000 years ago, along with nearly all other megafauna species. Whether the final extinctions in this process were driven primarily by climate change or human overhunting remains heavily debated.But in New Guinea, the evidence is mounting towards a rather different story. At the Nombe rockshelter, in the highlands of eastern Papua New Guinea, fossils of Protemnodon tumbuna show it lived locally until 22,000 to 27,000 years ago, during the last ice age. More evidence of late-surviving Protemnodon tumbuna in New Guinea came in 2024 with the discovery of a single tooth from Lachitu cave, located in the foothills of the Oenake Range, on the northwest coast of Papua New Guinea.The tooth had come from a limestone deposit dated 18,000 years old or younger, although it’s unclear whether the tooth itself was also that recent.In 2004, archaeological excavations at Taora – a rockshelter just west of Lachitu – produced a large collection of well-preserved animal remains. After maximum sea levels receded 6,800 years ago, Taora was used intensely by people exploiting nearby marine and rainforest resources. Over the next 1,500 years, they rapidly built up a dense deposit of discarded bones and shells, and hundreds of small bone points that likely tipped fishing spears or arrows. Archaeological excavation at Taora rockshelter in 2004 which found the megafauna fossil. Anthony Barham Our discoveryWhile examining this rich collection to understand how ancient people had lived in the dense coastal rainforest, one bone stood out to us. It was from the finger of a macropodid – a member of the kangaroo family – but one much larger than any species of marsupial found in New Guinea today.Suspecting it represented an unrecorded species, we compared the specimen’s shape and size to as many extant and extinct macropodids as possible to determine which one it likely belonged to.The Taora fossil is clearly different to all currently living macropodids. It’s most similar to members of Protemnodon – specifically, the New Guinean species Protemnondon otibandus. This species is thought to be the ancient ancestor of Protemnodon tumbuna, for which no fossils of the finger bones are known.The fossil has some unique traits that distinguish it from other Protemnodon species, including very prominent projections above the area where this middle finger bone joins to the claw. But on the whole, it closely resembles many species in the genus. And since we know Protemnodon tumbuna was present in the local area (a few kilometres away), perhaps as recently as 18,000 years ago, the fossil from Taora most likely belongs to it. The giant kangaroo fossil from Taora, a finger bone which probably belongs to Protemnodon tumbuna. Loukas Koungoulos A story of extended survivalRead together with the existing evidence from Nombe and Lachitu, the Taora fossil shows people must have co-existed with some species of megafauna for tens of thousands of years. They would have done so while also developing agriculture and village-dwelling societies in New Guinea. That’s a far cry from the “overkill” model, which suggests the earliest First Nations people of Australia and New Guinea rapidly hunted all remaining megafauna to extinction.This doesn’t mean people couldn’t have contributed somehow to the extinctions. But it does point to a complex scenario and the key role of each species’ unique biology and ecology in how they fared against human hunting and finer-scale habitat change.On the north coast of New Guinea, both factors were likely at play. Studies of Protemnodon teeth from Mount Etna in central eastern Queensland have found these kangaroos had small home ranges. They didn’t move far in order to forage or migrate, a tendency that would leave them extremely vulnerable to habitat loss. Drying climates over the past few hundred thousand years steadily shrank their highland rainforest habitat in New Guinea – and stimulated the rapid growth of nearby human populations. Eventually, the habitat became so small it couldn’t support a viable population of these ancient kangaroos. Trapped and unable to reach their increasingly distant home, the last giant kangaroos of New Guinea’s north coast would have quickly succumbed to even light hunting pressure, joining other rare marsupials that disappeared from this region at the same time in the face of post-glacial environmental changes.As we continue to uncover the fossil secrets of this remote section of New Guinea, there may yet be more twists in the story of Australia and New Guinea’s shared palaeohistory.Loukas Koungoulos received funding for this work from the Australian Research Council.Isaac A. R. Kerr receives funding from the Australian Research Council, the Australia & Pacific Science Foundation, and the Elaine Bailey Palaeontology Expeditions fund.Sue O'Connor received funding for this work from the Australian Research Council.