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Extinctions stemming from environmental change often trigger trophic cascades and coextinctions. Bottom–up cascades occur when changes in the primary producers in a network elicit flow‐on effects to higher trophic levels. However, it remains unclear what determines a species' vulnerability to bottom–up cascades and whether such cascades were a large contributor to the megafauna extinctions that swept across several continents in the Late Pleistocene. The pathways to megafauna extinctions are particularly unclear for Sahul (landmass comprising Australia and New Guinea), where extinctions happened earlier than on other continents. We investigated the potential role of bottom–up trophic cascades in the megafauna extinctions in Late Pleistocene Sahul by first developing synthetic networks that varied in topology to identify how network position (trophic level, diet breadth, basal connections) influences vulnerability to bottom–up cascades. We then constructed pre‐extinction (~80 ka) network models of the ecological community of Naracoorte, south‐eastern Sahul, to assess whether the observed megafauna extinctions could be explained by bottom–up cascades. Synthetic networks showed that node vulnerability to bottom–up cascades decreased with increasing trophic level, diet breadth and basal connections. Extinct species in the Naracoorte community were more vulnerable overall to these cascades than were species that survived. The position of extinct species in the network – tending to be of low trophic level and therefore having relatively narrow diet breadths and fewer connections to plants – made them vulnerable. However, these species also tended to have few or no predators, a network‐position attribute that suggests they might have been particularly vulnerable to new predators. Together, these results suggest that trophic cascades and naivety to predators could have contributed to the megafauna extinction event in Sahul. [ABSTRACT FROM AUTHOR]

Understanding of Late Pleistocene megafaunal extinctions in Australia and New Guinea (Sahul) suffers from a paucity of reliably dated bone deposits. Researchers are divided as to when, and why, large-bodied species became extinct. Critical to these interpretations are so-called 'late survivors', megafauna that are thought to have persisted for tens of thousands of years after the arrival of people. While the original dating of most sites with purported late survivors has been shown to have been erroneous or problematic, one site continues to feature: Cloggs Cave. Here we report new results that show that Cloggs Cave's youngest megafauna were deposited in sediments that date to 44,500–54,160 years ago, more than 10,000 years older than previously thought, bringing them into chronological alignment with the emerging continental pattern of megafaunal extinctions. Our results indicate that the youngest megafauna specimens excavated from Cloggs Cave datedate to well before the Last Glacial Maximum (LGM), and their demise could not have been driven by climate change leading into the LGM, the peak of the last Ice Age. • The extinct megafauna remains from Cloggs Cave, a key 'late survival' Late Pleistocene megafauna site in SE Australia, are now conclusively shown to be older than 44,500 years old, more than 10,000 years older than previously thought. • We present 69 new AMS 14C and 10 new single-grain OSL ages from excavations undertaken in 2019–2020 at Cloggs Cave, to reveal significant new data on the deposit's chronostratigraphy, on what is now one of Sahul's best-dated archaeological sites. • We show that no purported 'late survival' extinct Late Pleistocene megafauna remains in Sahul are demonstrably significantly younger than c. 40,000 years old. • We argue that understanding Late Pleistocene megafaunal extinctions requires extensive chronostratigraphic examination of purported 'late survival' remainsthe. [ABSTRACT FROM AUTHOR]