Australia - how giants fell

What wiped out the giants of Australia that preceded the kangaroo, the wombat and the contemporary emu?

By: Yonat Ashchar and Noam Levithan

Once a year, the International Day for Biological Diversity is celebrated, which aims to increase and raise awareness of the many animals and plants that are in danger of extinction. This record deals with the reasons for the extinction of the giant animals that lived tens of thousands of years ago in Australia.

Australia is known for its special animals. On this continent is found a considerable percentage of the marsupials alive today, and also the only representatives of the billed mammal series - the duck and hedgehog families (which are also found in Tasmania and the islands of Papua New Guinea). But this special fauna was many times richer and more diverse tens of thousands of years ago and particularly rich in large species: then the Procoptodon roamed the Australian bush (procoptodon), a three-meter-tall kangaroo that reached a weight of 230 kg, and even dwarfed the Diprotodon (Diprotodon), a wombat-like marsupial that reached a weight of more than two and a half tons. Next to them runs the chicken (which does not fly) Geniornis (Genyornis), two meters high. What happened to them, and to more than 50 species of large animals (mammals, birds and even reptiles)? When did they disappear, and why?

Over the years, researchers have pointed to two main factors as suspects in the extinction of Australia's large animals: the climate and humans. Humans first arrived in Australia about 45 to 60 years ago, and there is no arguing that the Great Extinction occurred some time after that. But how long? Was it a short event (in geological terms), in which humans hunted the animals until their extinction, or did the animals become extinct one after the other, in a period of about 10,000 to 20,000 years, as a result of climate changes and various environmental pressures?

In this debate, a place of honor is reserved for the Cuddie Springs archaeological site, the only site where fossils of the extinct animals were found alongside human tools. Several studies were done on the findings at this site, and from some of them the researchers concluded that between the animal fossils and the tools there is an overlap of up to 15,000 years - that is, humans lived alongside the large animals for a long time. This was one of the strongest pieces of evidence for the theory of slow extinction over time, in which man played only a marginal role.

In a study published in the quarter Quaternary Science Reviews, Rainer Grün and his colleagues from Australia and England challenge this conclusion. They used a new dating method, Electron spin resonance. This method makes it possible to date not only the rocks alongside the bones and tools, but also the fossilized teeth themselves, and is based on testing the amount of radioactive radiation absorbed by the enamel in the teeth when it was buried in the ground. Radioactive elements are found in the soil naturally (at a very low level) and by checking the level of radiation in the area it is possible to calculate how many years the teeth have absorbed the radiation, i.e. how old they are. The calculations of Gron and his colleagues showed that all the fossils are more than 50,000 years old, that is, older than some of the previous studies suggested. The confusion probably arose from the fact that the soil of the Caddy Springs site had been disturbed in the past and different layers had mixed with each other. This fact meant that the previous dating methods, which were based on dating the soil in the same layer where the fossils were found, produced incorrect results.

The new dating matches the dates of fossils from other sites in Australia, and together they indicate a relatively rapid extinction shortly after the arrival of humans. This does not prove that humans were responsible for the extinction - it is possible that the animals became extinct in a later period but did not adapt, and it is also possible that the extinction occurred simultaneously with the arrival of humans but was caused by other factors. However, there is no doubt that the new study strengthens the hypothesis that the blame for the extinction of the giants lies with humans, whether due to direct hunting or due to habitat modification.

Director 2013 An article was published in PNAS who reviewed the evidence related to the extinction of the Australian giants. According to the review, most species of large animals disappeared even before the first humans arrived in Australia. Out of about 90 species of giant animals, only between 8 and 14 species still lived on the continent when man arrived. It is possible that the remaining giants did become extinct due to the fault of humans, but it seems that the main cause of the extinction of most large animals is the climate. The article states that for about 400,000 years unstable weather prevailed in Australia and a desertification process took place during which the animals disappeared, so that when humans arrived on the continent almost all the giants were already extinct or were on the verge of extinction.

Finally, we note that the rapid extinction of animals due to the arrival of humans in a new area is not limited only to Australia. For example, there are quite a few known cases of birds that became extinct when the early settlers arrived in the islands of the Pacific Ocean and especially in New Zealand where, among other things, the great moa became extinct. The most striking example is the North American continent, which also experienced a large-scale extinction of large animals, including mammoths and mastodons, near the arrival of the first humans. Even there there is still a debate about the causes of extinction and the role that humans played.

The original article appears in Galileo magazine 139, March 2010 and was updated on Dr. Noam Levitan's blog SciPhile

for further reading

The original article:

Grün, R., Eggins, S., Aubert, M., Spooner, N., Pike AWG & Müller W. ESR and U-series analyzes of faunal material from Cuddie Springs, NSW, Australia: implications for the timing of the extinction of the Australian megafauna. Quaternary Sci. Rev. 29, 596-610 (2010). doi: 10.1016/j.quascirev.2009.11.004

On endangered animals: Ido Livan, "It's a very small world", "Galileo" 177.