Why did the Australian megafauna go extinct?


Quote:

New study challenges a major theory on why some kangaroos mysteriously went extinct The extinction of the megafauna – giant marsupials that lived in Australia until 60,000 to 45,000 years ago – is a topic of fierce debate. Some researchers have suggested a reliance on certain plants left some species susceptible to changes in climate. Our research, published today in Science, indicates that for short-faced kangaroos, which comprise the bulk of the extinct megafauna, their diets were broad and comparable to many long-faced kangaroos which survived the extinction event. Broad diets would have made short-faced kangaroos well adapted to the last ice age in Australia, bringing diet-based extinction scenarios into doubt.

The research paper is here: http://www.science.org/doi/10.1126/science.adq4340

If it wasn’t an ice age and change in food available then what caused the megafauna extinction?



Quote:

What was the Australian megafauna? Megafauna is a loose term referring to all the species present in the Pleistocene of Australia (2.6 million to 12,000 years ago) which haven’t survived until today. Two features unite them: a generally large body size and being extinct. By 40,000 years ago, 90% of large species in Australia had died out. This included giant flightless birds, the rhino-sized marsupial Diprotodon, marsupial lions and many others.

Naracoorte limestone cave has a skeleton of a marsupial bear with the skeleton of a huge python wrapped around it. Impressive!


Quote:

To investigate this idea, we used a method called dental microwear texture analysis. When an animal chews its food, the food leaves microscopic scratches on its teeth. The shape of these scratches changes based on the physical properties of the food: grasses typically make thin scratches, while leaves create deeper gouges. By scanning the teeth under a fancy microscope called a confocal profiler, we end up with a 3D-scan of a tiny area of the tooth surface, which can then be analysed using algorithms that quantify its texture. To see how microwear relates to diet, we compiled a massive baseline of modern macropods whose diets we know really well. This included 17 species, from browsers (like quokkas, mostly eating the leaves of shrubs), through mixed feeders (like red-necked wallabies, eating large contributions of browse and grass) to grazers (like red kangaroos, who mostly eat grass). To understand diets in the Pleistocene, we looked at fossils from Victoria Fossil Cave in the Naracoorte Caves World Heritage Area. We found overall there was a high degree of mixed feeding taking place at Naracoorte in the Pleistocene. Four species of short-faced kangaroos and three species of long-faced kangaroos all had very similar diets – they were mixed feeders. This alone dispels the notion that all short-faced kangaroos were driven extinct as a direct result of a restricted diet. Mixed feeding is a common strategy among kangaroos today, especially in parts of Australia with more vegetation. It allows species to adapt their diets to changing conditions and mixed environments.To investigate this idea, we used a method called dental microwear texture analysis. When an animal chews its food, the food leaves microscopic scratches on its teeth. The shape of these scratches changes based on the physical properties of the food: grasses typically make thin scratches, while leaves create deeper gouges. By scanning the teeth under a fancy microscope called a confocal profiler, we end up with a 3D-scan of a tiny area of the tooth surface, which can then be analysed using algorithms that quantify its texture. To see how microwear relates to diet, we compiled a massive baseline of modern macropods whose diets we know really well. This included 17 species, from browsers (like quokkas, mostly eating the leaves of shrubs), through mixed feeders (like red-necked wallabies, eating large contributions of browse and grass) to grazers (like red kangaroos, who mostly eat grass). To understand diets in the Pleistocene, we looked at fossils from Victoria Fossil Cave in the Naracoorte Caves World Heritage Area. We found overall there was a high degree of mixed feeding taking place at Naracoorte in the Pleistocene. Four species of short-faced kangaroos and three species of long-faced kangaroos all had very similar diets – they were mixed feeders. This alone dispels the notion that all short-faced kangaroos were driven extinct as a direct result of a restricted diet. Mixed feeding is a common strategy among kangaroos today, especially in parts of Australia with more vegetation. It allows species to adapt their diets to changing conditions and mixed environments.

https://theconversation.com/new-study-challenges-a-major-theory-on-why-some-kangaroos-mysteriously-went-extinct-246681

The Pleistocene ice age was not nearly as severe in the Southern hemisphere as in the north, no glaciation here etc.

Still leaves the question; what DID kill off the megafauna?

Quote:

The extinction of the megafauna – giant marsupials that lived in Australia until 60,000 to 45,000 years ago – is a topic of fierce debate.

Take a wild guess.....

https://www.unsw.edu.au/content/unsw-sites/au/en/newsroom/news/2018/08/when-did-aboriginal-people-first-arrive-australia/_jcr_content/root/responsivegrid-layout-fixed-width/responsivegrid-full-top/column_layout_1/par_2_1_75/column_layout/par_1/column_layout/par_1/image.coreimg.82.700.jpeg/1706847627852/2023-03-image5b.jpeg

Map of the original colonisation of Australia showing different genetic markers carried by Aboriginal populations (in red), and the vegetation zones at the time. Archaeological dates are shown in black, with 1 kya = 1,000 years ago.
Image: Nature, Tobler et al.


https://www.unsw.edu.au/newsroom/news/2018/08/when-did-aboriginal-people-first-arrive-australia

Yet cougars and black, grey and white bears still live in northern America despite human settlement there and severe glaciation. Elephants, hippos and rhinos still live in Africa.

Clarke goes on to determine that the damaged condition of the ancient marsupial fossils suggests extinction by ‘violent catastrophe’ rather than by gradual ‘quiet death’. The catastrophe he asserts could have been a flooding deluge given the 25 feet of ironstone rubble and clay under which the fossils were buried. Leichhardt had a converse view believing that the draining of swamps associated with uplift was the most likely cause of their demise (Leichhardt, 1847).Owen had a different explanation for the demise of the giant Australian mammals.

No other adequate cause suggests itself save the hostile agency of man …. As the elephant succumbs to the spears and pitfall of the negro hunters, the minor bulk of Diprotodon is not likely to have availed it against the combined assaults of the tribes of Australoid wielders of club and throwing-sticks (Owen, 1877).

Owen’s opinion and Clarke’s insight foreshadow the contemporary debate embroiling the fate of Diprotodon and the other megafauna. Some researchers argue that their sudden demise, coincident with the arrival of humans, indicates they were exterminated by a blitzkrieg of hunting (Roberts  et al., 2001; Roberts and Brook, 2010). Other schools of thought provide evidence of coexistence between megafauna and humans (Trueman et al., 2005) or gradual decline, suggesting extinction was ultimately related to a drying climate (Price et al., 2011).
https://www.researchgate.net/publication/256440954_Ludwig_Leichhardt_and_the_significance_of_the_extinct_Australian_megafauna

So sea level rise due to some climate change caused the extinction of the megafauna?

What about the megafauna of the Americas? Mastodons and mammoths disappeared leaving the “small” elephant as the only member of that family. Climate change there is sufficient explanation with man just a minor factor.