Re-evaluating the evidence for late-surviving megafauna at Nombe rockshelter in the New Guinea highlands

The causes of the Late Pleistocene extinction of most larger-bodied animals on the Australian continent have long been controversial. This is due, in no small part, to inadequate knowledge of exactly when these species were lost from different ecosystems. The Nombe rockshelter in the highlands of Papua New Guinea is one of very few sites on Sahul with as-yet-unrefuted evidence for the survival of megafaunal species until more recently than 40 thousand years (ka) ago. However, our understanding of the age of this site has been based on radiocarbon dating. Here we present new U–Th ages on large marsupial specimens from the deposit and identify a range of postcranial elements to species that include the diprotodontid Hulitherium tomasettii, kangaroo Protemnodon tumbuna and thylacine Thylacinus cynocephalus. Direct U–Th ages of 27–22 ka ago on faunal remains of Protemnodon tumbuna and another large unidentified macropodid are consistent with the existing radiocarbon chronology, yet are minimum ages due to the potential for post-depositional uptake of ²³⁸U and stratigraphic reworking. Pollen analyses indicate perhumid, montane forests dominated by Nothofagus persisted, with minimal human disturbance from at least c.26–20 ka ago up to the terminal Pleistocene. Collagen fingerprinting (ZooMS) demonstrates the potential of protein-based identification of megafaunal remains at Nombe in the future. This study leaves open the possibility of extended coexistence between some megafaunal species in the montane rainforests of New Guinea and intermittently visiting groups of people, and underscores the need for further investigation of the Nombe deposit. Although preliminary, these findings reinforce the view that debates regarding megafaunal extinctions on Sahul require a greater appreciation of species-specific temporalities and the degrees of human impact on diverse habitats across the continent.