Extreme environmental change was the most likely cause of extinction of megafauna in Sahul, the supercontinent formed by Australia and New Guinea during periods of low sea level, according to an analysis of megafauna fossils from the site of South Walker Creek near the township of Nebo, Australia.
A range of now extinct megafauna that was present when humans first arrived in Australia. Image credit: Peter Trusler, Monash University.
South Walker Creek, the youngest megafauna site in northern Australia, was once home to at least 16 species of megafauna, including thirteen extinct and three extant species.
Carnivorous megafauna was represented by the marsupial lion (Thylacoleo), at least three crocodilians (Crocodylus porosus, Pallimnarchus sp. and Quinkana sp.) and two giant monitor lizards (Varanus priscus or Megalania and a Komodo dragon-sized species).
Plant-eating megafauna was diverse with two species of wombats, one palorchestid marsupial, two diprotodontids, the emu (Dromaius novaehollandiae), and five species of kangaroos.
One kangaroo species was 2.5 m tall and had an estimated mass of 274 kg, this makes it the largest kangaroo of all time.
“The megafauna at South Walker Creek were uniquely tropical, dominated by huge reptilian carnivores and mega-herbivores that went extinct around 40,000 years ago, well after humans arrived onto mainland Australia,” said Dr. Scott Hocknull, a paleontologist at Queensland Museum and the University of Melbourne.
“While the rest of the world had giant carnivores like saber-toothed cats, bears and hyenas, Australia’s predators were mostly giant reptiles, including an extinct freshwater croc around 7 m long, a relation to the modern salt water crocodile and a land-dwelling crocodile,” he added.
“There were also two giant lizards including a 6-m-long lizard called Megalania and another giant lizard, similar in size to the Komodo dragon.”
Megafauna species from main South Walker Creek fossil sites SW9, SWJ and SW3 with downstream site SWCC (indicated by arrow). Scale bars – 1 mm in (g, i); 5 mm in (h, j-t, v, x); 10 mm in (u); and 50 mm in (w). Image credit: Hocknull et al, doi: 10.1038/s41467-020-15785-w.
“We cannot place humans at this 40,000-year-old crime scene, we have no firm evidence. Therefore, we find no role for humans in the extinction of these species of megafauna,” Dr. Hocknull said.
“Instead, we do find that their extinction is coincident with major climatic and environmental deterioration both locally and regionally, including increased fire, reduction in grasslands and loss of freshwater.”
“Together, these sustained changes were simply too much for the largest of Australia’s animals to cope with.”
The study was published in the journal Nature Communications.
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S.A. Hocknull et al. 2020. Extinction of eastern Sahul megafauna coincides with sustained environmental deterioration. Nat Commun 11, 2250; doi: 10.1038/s41467-020-15785-w
