Fate of Australian Megafauna Discovered through Prehistoric Dung

The megafauna of Australia before the extinctions was quite different than that of today. Clockwise from top left: Genyornis; Diprotodon (a rhino-sized wombat); Procoptodon (the largest-ever kangaroo); the thylacine; Thylacoleo (the biggest marsupial carnivore); and the giant lizard, Megalania. Courtesy of Science Magazine.

50,000 years ago, a trip to Australia would have been quite a different experience from that of one today. Towering kangaroos and ostriches, lumbering rhino-sized wombats and marsupial “lions,” as well as over-5-meter-long lizards would greet any vacationer to the small continent. However, as any Australian native or recent visitor to the land down-under could attest, these unique animals are now nowhere to be seen, except for in the fossil record.

Around 40,000 years ago, these Australian megafauna (“mega” for size and “fauna” for animals) and many other megafauna across the globe all went extinct, for reasons that are highly debated. The many hypotheses for the cause of the extinctions include environmental factors such as catastrophes or habitat loss, and human impacts such as habitat alteration, introduction of predators or diseases, or rapid or prolonged predation by human immigrants. Although many studies have analyzed these different hypotheses, few have looked into the consequences of the extinctions, especially since the interactions between herbivores and vegetation can affect the structure, composition, and dynamics of plant communities in many ways. Herbivores help prevent forest fires by maintaining vegetation openness and patchiness. They also stimulate growth by dispersing seeds and recycle nutrients by disturbing soil.

An artist’s representation of a megafauna cave bear. Courtesy of Marcos Carvalho.

A recent study in Science has attempted to break the imbalance in megafauna studies by analyzing Australian sediments that contained a temporally resolved record of the Australian environment. Based on the extreme decline of a fungus that grows predominantly in the dung of large herbivores, the scientists, led by Susan Rule of the Australian National University, detected that the extinctions occurred about 41,000 years ago. They noted that plant fossils in the sediments of this age do not indicate any climatic shifts. This led them to conclude that humans, who are thought to have arrived in Australia around 49,000 years ago, hunted the megafauna to extinction.

Additionally, the study noted that charcoal levels in the sediments of the time period greatly increased following the extinctions, indicating that the absence of these large herbivores led to an increase in the number and intensity of natural fires. Although the fires could have been anthropogenic, their coincidence with the extinctions and the absence of similar fires before the extinctions make it very unlikely.

Archaeologist Dr. Judith Field from the University of New South Wales is concerned with the use of the fungus as a proxy for the herbivores. Since this fungus has only ever been found in the dung of modern taxa, it is difficult to say with certainty that Australian megafauna also would have had the same fungus in their dung. Additionally, Field questions the conclusions the scientists have made about large-scale human hunting, since evidence for temporal overlap between the humans and the megafauna is limited and the fossil record lacks evidence of large-scale human hunting. These challenges suggest that the mystery of megafauna extinctions may still be up for debate.

Nonetheless, this study has taken a new approach that may lead to further answers. It begins an exciting trend of examining both the causes and the consequences of extinctions.

More drawings by Carvalho can be found here.