Climate change frames debate over the extinction of megafauna in Sahul (Pleistocene Australia-New Guinea)

Abstract

Around 88 large vertebrate taxa disappeared from Sahul sometime during the Pleistocene, with the majority of losses (54 taxa) clearly taking place within the last 400,000 years. The largest was the 2.8-ton browsing Diprotodon optatum, whereas the ∼100- to 130-kg marsupial lion, Thylacoleo carnifex, the world's most specialized mammalian carnivore, and Varanus priscus, the largest lizard known, were formidable predators. Explanations for these extinctions have centered on climatic change or human activities. Here, we review the evidence and arguments for both. Human involvement in the disappearance of some species remains possible but unproven. Mounting evidence points to the loss of most species before the peopling of Sahul (circa 50-45 ka) and a significant role for climate change in the disappearance of the continent's megafauna.

Keywords: Pleistocene extinctions; archaeology; faunal turnover; human colonization; megafauna extinction.

Fig. 1.

Thylacoleo carnifex, the 100- to 130-kg marsupial lion with massive “bolt cutter-like” cheek teeth and the most powerful bite for its size of any mammalian carnivore, was a formidable predator of large animals. (Drawing by Peter Schouten.)

Fig. 2.

Sites mentioned in the main text. The continental limits of Sahul are defined by the −130-m bathymetry line, and Sahul incorporates Australia, New Guinea, and Tasmania. The Nullarbor Plain caves contain middle Pleistocene fossil deposits. Kings Creek is located in the eastern Darling Downs region.

Fig. 3.

Extinction chronology of Pleistocene megafaunal taxa in Sahul (88 species). For many species, terminal dates are debated, as is the definition of a “secure” date. If the selection criteria of Roberts et al. (9) are applied, as few as 8 species clearly survived to the time of human colonization of Sahul. Species reported to overlap with humans but lacking contextual information linking the dates to the taxa in question are illustrated in gray. The majority of taxa cannot be placed within the time frame of human arrival, and many lack reliable radiometric dates altogether, with some of the taxa claimed to have been the victims of human-mediated extinction known only from the Pliocene (e.g., Euryzygoma dunense). Of those taxa known to overlap with people, some persist well beyond a previously proposed 51- to 39-ka “extinction window” (9), whereas most of those falling within this window are not securely linked to the dates (six of nine taxa). Of those taxa potentially surviving until more recently than ∼50 ka, almost half are from New Guinea.

Fig. 4.

Late Pleistocene temporal occurrences of megafauna from the intensively sampled Kings Creek Catchment, Darling Downs, southeastern Queensland (13), in relation to the hypothesized continental megafaunal extinction window and earliest evidence of human colonization. Rarefaction, bootstrapping, and associated statistical analyses demonstrate that the apparent temporally progressive loss of megafauna was a real phenomenon and cannot simply be explained as a result of taphonomic or sampling biases (14). Importantly, the data clearly point to prehuman climate changes as a driver of the losses and do not support the hypothesis that there was a local mass extinction of all megafauna at or around the hypothesized extinction window.

Fig. 5.

The EDC δD (‰) record over the last 900 ka (–47) illustrates the trend toward increasingly warm interglacials (red line) and increasingly cold glacial maxima (blue line) beginning at around 400 ka. (Upper) Graphic depicts the number of species that are not represented thereafter in the fossil record in the following temporal bins: >400 ka or undated, 400–126 ka, 126–51 ka, 51–39 ka, and <39 ka. Species with last appearance dates before human arrival (50–45 ka) are highlighted in green, and those with last appearance dates after this are highlighted in blue. There is little evidence for any extinction pulse associated with human arrival.