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Megafauna

Humans arrived in Australia about 55,000 years ago, some 50 million years after the Australian land mass Sahul had separated from the Asian land mass Sunda, at a time when Australia’s distinctive marsupials were evolving.

Giant Wombat (Diprotodon optatum) - restoration

Giant Wombat (Diprotodon optatum) – artistic impression
Courtesy Wikimedia Commons

Palaeontologist and environmentalist Tim Flannery paints a picture of the giant animals (known as ‘megafauna’ the figure of 40-44 kg is sometimes used as a quantitative measure of ‘giant’) present in the Pleistocene when Australia was first settled. Megafauna should not be confused with dinosaurs which became extinct about 65 M years ago but the megafauna only tens of thousands of years ago when they were widespread across most of Australia except the northern rainforest and arid zone:

Back then Australia was home to an enormous array of giant marsupials, birds and reptiles including marsupial equivalents of rhinoceros, hippopotamus, giant sloths, leopards and antelopes. They shared the land with giant emu-like birds, huge goannas, horned turtles and gigantic primitive snakes, as well as the distinctive species of today, such as kangaroos and koalas.

A few of these ancient animals are depicted in Aboriginal rock art and some also resemble creatures like the giant kangaroo that are described in the oral tradition of the Dreamtime.[9][13]

And then, a few thousand years after human arrival:

“. . . a rapid and dramatic extinction had stripped the continent of this marvellous diversity of megafauna, leaving nothing larger than a human or a red kangaroo.  In all, about sixty species of giants vanished, along with an as yet uncounted number of lesser creatures … By eating vegetation that would otherwise burn, the marsupial giants had suppressed fire.  They recycled the few nutrients available in the vegetation through their guts, pouring out fertilizer in the form of manure and urine, thereby increasing the carbon content of the soils, enhancing soil moisture and promoting plant growth.  With their extinction however, the grasses and bushes grew rank and fires raged, baring soils, causing erosion and destroying nutritious but fire-sensitive plants . . . overall productivity most probably diminished ten- or a hundredfold . . . Australia became a land of fire, whose soils grew ever more impoverished . . . it may have influenced Australia’s climate.
Flannery Here on Earth 2010 pp. 82–83

In a scientific paper published in 1990 Flannery proposed this sequence of events: extermination of the herbivore megafauna with consequent rank growth of woody vegetation that was subsequently fired leading to a preponderance of fire-resistant, even fire-dependant, species.[10]

Megafauna extinctions on other continents

Extinctions of megafauna, especially those tame animals and birds unfamiliar with humans, occurred world-wide (with the exception of Africa and southern Asia) in the late Pleistocene: in America the mammoth, mastodon and giant sloths (12,500-11,000 BP)[6]; on Mauritius (Reunion), between 1598 and 1662, the massive Dodo (to about 1 m tall and weighing to 18 kg) was wiped out by Dutch sailors who had guns and released pigs that ate the eggs; in New Zealand the nine species of Moa, also wingless emu-like birds the largest standing 3-4 m tall, are assumed to have been hunted to extinction by 1400 CE, shortly after the arrival of the Maori, the earliest archaeological record dating to 1,280 CE;[5] in Australia the flightless giant emu-like Genyornis became extinct, possibly from human hunting, about 50,000 BP. However, in America (where human occupation was much more recent) mammoths survived until the end of the Pleistocene whereas in Australia all but the Red Kangaroo were extinct by 22,000 BP. In Patagonia a narrow megafaunal extinction phase 12,280 ± 110 years ago occurred as sabre-toothed cats, one-tonne bears and giant sloths coexisted with humans for up to 3,000 years but were extinct within 300 years of rapid climate warming. In Australia there is a prolonged period of overlap of about 11,000 years between humans and megafauna placing the extinction due to humans theory (known as Blitzkreig) in question. Both climate and humans appear to be imprtant factors influencing extinction.[22]

Giant animals were important for their interaction with the vegetation. On the one hand large herbivorous browsers would have gone but, on the other, ther would probably have been an increase in the number of small herbivores that had formerly been taken by giant carnivores, although it was not just the megafauna that had died out it was also many terrestrial vertebrates from a wide varietyu of habitats from deserts to forests.

Human occupation of Timor c. 42,000 BP led to the rapid demise of the island’s megafaunal species – Stegodon, Komodo dragon and giant tortoise. However, in Java human impact on the fauna seems minor until the mid-Holocene with the introduction of agriculture and large-scale clearing, with animals such as elephant, tiger and rhino only disappearing from many areas within historic times.[3]

Giant Wombat (Diprotodon optatum)
Artistic impression
Courtesy Wikimedia Commons – Accessed 15 Mar. 2019

A few of these ancient animals are depicted in Aboriginal rock art and some also resemble creatures like the giant kangaroo that are described in the oral tradition of the Dreamtime.[9][13]

And then, a few thousand years after human arrival:

“. . . a rapid and dramatic extinction had stripped the continent of this marvellous diversity of megafauna, leaving nothing larger than a human or a red kangaroo. In all, about sixty species of giants vanished, along with an as yet uncounted number of lesser creatures . . . By eating vegetation that would otherwise burn, the marsupial giants had suppressed fire. They recycled the few nutrients available in the vegetation through their guts, pouring out fertilizer in the form of manure and urine, thereby increasing the carbon content of the soils, enhancing soil moisture and promoting plant growth. With their extinction however, the grasses and bushes grew rank and fires raged, baring soils, causing erosion and destroying nutritious but fire-sensitive plants . . . overall productivity most probably diminished ten- or a hundredfold . . . Australia became a land of fire, whose soils grew ever more impoverished . . . it may have influenced Australia’s climate.

Flannery Here on Earth 2010 pp. 82–83

In a scientific paper published in 1990 Flannery proposed this sequence of events: extermination of the herbivore megafauna with consequent rank growth of woody vegetation that was subsequently fired leading to a preponderance of fire-resistant, even fire-dependant, species.[10]

Late Pleistocene extinctions in Australia

Demise of the Australian megafauna, whatever its cause, occurred long before the Pleistocene extinctions in Europe and North America.

Marsupial Lion (Thylacoleo carnifax) - restoration

Marsupial Lion (Thylacoleo carnifax) – artistic impression
Courtesy Wikimedia Commons

A large jaw discovered in Wellington Cave in Sydney’s Blue Mountains in 1830 was sent to Richard Owen at the British Museum and he named it Diprotodon, a complete skeleton being unearthed in 1847 in southern Queensland.[18] Australian megafauna was generally smaller than that of other continents. While woolly mammoths and sabre tooth tigers were roaming Europe the Australian megafauna included marsupial (pouch-bearing) animals like the marsupial lion (Thylacoleo carnifex) and the mega grey kangaroo (Micropus giganteus titan), monotremes (mammals that lay eggs), testudines (turtles), monitor lizards (like Varanus priscus), a 5-metre-long snake (Wonambi naracoortensis) a giant Wombat )(Diprotodon optatum) reaching the size of a rhinoceros and weighing up to 2,500 kg, a saltwater crocodile up to 7 m long and weighing up to 770 kg (Crocodylus porosus), and giant flightless birds like Genyornis and Dromornis.

In spite of former difficulties in dating archaeological evidence a 2001 study using more accurate optically stimulated luminescence and uranium-thorium dating techniques concluded that the Australian megafauna, mostly browsing and grazing diprotodonts and macropods, did indeed disappear from the fossil record about 46,000 years ago in a sudden extinction event.[8] However, the reason(s) for this extinction remain unclear, generally being related to climatic factors, most notably the onset of aridity, possibly Aboriginal hunting practices, simply hunting them to extinction (the ‘overkill’ hypothesis) or affecting vegetation and the food chain by their use of fire – or perhaps a combination of these and/or other factors. Once the population had contracted further hunting would have accelerated the process of extinction.

Human populations were established over most of the continent by at least 47 ka.[19]

Burned eggshell fragments of the 200 kg flightless bird Genyornis newtoni have been found at more than 200 sites across Australia around transient campfires that were presumably used to cook the eggs. These only occur between 53.9 and 43.4 ka and likely before 47 ka thus indicating megafaunal predation by humans as they dispersed across the continent.[20] Lack of evidence for unprecedented climate change between 60 and 40 ka and survival of megafauna during earlier more extreme climate fluctuations suggests that climate change was not the only cause of megafaunal extinction. Rather, human impact is a more likely scenario with increasing aridity having a lesser effect.[21]

Tasmanian Devil & Tasmanian Tiger

It is probable at least 12 species of larger marsupial coexisted with man and become extinct. Other animals of interest include the Tasmanian Tiger and Tasmanian Devil which lived on the mainland long after the death of the megafauna but became extinct before the arrival of Europeans, though surviving on Tasmania for a while.[1] Dingos thrived on the mainland but never reached Tasmania.[2] Aboriginals and dingoes may have been responsible for the extinction of the Tasmanian Devil on the mainland.[4]

As a footnote it can be added that at least 23 mammals have become extinct in Australia since European settlement, one third of the world’s mammal extinctions occurring in Australia after 1940.

Aridity

Onset of aridity no doubt had serious effects on megafauna habitat, increasing significantly during the period of peak glaciation in the last ice age about 18,000 years ago when large inland swamps and lakes critical for these bulky animals disappeared. However, the apparent sudden extinction of megafauna about 46,000 years ago, just after human occupation of the continent. needs special evidence as they had endured climatic variation, including arid glaciation periods, for two million years previously.

Finds at different localities point to possible different causes. Evidence from the chemical analysis of shells of emu and extinct giant birds at Coral Bay in WA indicate a sudden change of vegetation at around this time, indicating an onset of aridity on a wide scale perhaps sufficient to reduce population numbers. And as herbivores diminish so too do the carnivores that feed on them.

In contrast, detailed analysis of the egg shells of the currently-existing emu (Dromaius novaehollandiae) and extinct Genyornis newtoni at Lake Eyre show that the emu shells have been present for 120,000 years up to the present day while those of Genyornis disappear about 45,000 years ago during a period of comparatively mild climate suggesting human influence.[11] ‘Birds were trapped, netted, snared, boomeranged, lassoed, strangled or clubbed after being detected and enticed in many ingenious ways’.[16]

Hunting

It would also appear that around this time Aboriginals were dispersing throughout the continent and it is possible that the steady culling of the young animals was sufficient to reduce populations. A 15-year study by Judith Field of an archaeological site in Cuddie Springs, NSW has megafaunal remains and human artifacts together, linking animal hunting to humans. It seems that there may have been a reciprocal influence of aridity and culling by Aboriginals perhaps combined with the widespread use of firestick farming. Some support of this suggestion lies in the persistence of the megafauna on Tasmania for about 5,000 years longer than on the mainland but its disappearance when humans arrived. Evidence for the use of fire in charcoal deposits from this period is ambiguous.

Flannery goes on to suggest that the deciduous rainforest of northern Australia possibly enhanced rainfall by transpiring moisture but when burned this capacity was lost “ … and so the great lakes that lie at the continent’s heart dried up”.

Aboriginals may have altered vegetational distribution through their interaction with giant marsupials, especially those that were herbivores.

Hunting involved elaborate hand signals and gestures. Fish were caught with a hook and line, the hook sometimes made from shell or bone and elaborate nets made of plant fibre. In coastal areas shellfish were eaten in large quantities, the remaining shells heaped together and remaining as middens along the coast, the tallest structures constructed by Aboriginals.[17]

Fire

Burning has been identified as a way that the megafauna was decimated although Flannery argues that before human occupation the giant herbivores cropped the vegetation so effectively as to decrease the likelihood of conflagrations, the intense fires only returning after the demise of the megafauna when hunted to extinction by Aboriginals.

Extinction of the megafauna may have had significant consequences for both the distribution of vegetation and the continent’s fire impacts.

Commentary & sustainability analysis

In considering the impact of Aboriginals on the environment the extinction of the megafauna becomes significant because of the removal of major herbivores and predators from the food chain. The scale of this impact is uncertain but ecologists are clearly of the view that it might have been sufficient to have had an observable effect on the vegetation.

The precise reason for the global loss of these giant animals – from the Americas, Australia and Eurasia – is still the subject of debate although human hunting is most frequently suggested. In Africa and Eurasia with humans present long before the Pleistocene the picture is not so clear although in Africa about 50 big game species became extinct around 50,000 BP and this is seen as a probable result of human hunting.[14] Other possible causes (sometimes in combination) include: climate change, disease, and the atmospheric disturbance resulting from the impact of an asteroid or comet.

In Australia by the end of the Pleistocene the largest animal (over 50 kg) on the continent was Homo sapiens[15] but there is still no consensus among archaeologists and ecologists concerning the causes for the extinction of Australia’s megafauna. This may be because it involved a complex of factors, notably human hunting and the use of fire in combination with climate change.

In Australia archaeological evidence of the extinct megafauna is fragmentary and under constant revision as bone is difficult to date archaeological finds are based on less reliable stratigraphy. Perhaps the nearest to a consensus view is that Aboriginal burning produced vegetational change that severely altered the food supply and diet of these animals. Their size alone would have made them vulnerable to fire, being unable to sustain speed or find safe cover during the fire. Often slow creatures with large body mass this would make them susceptible to both fire and hunting. Some would have been relatively tame, making obvious game animals while the young, especially, would be prone to human predation which would have had an immediate impact on population numbers, especially in animals with a long gestation period.

Even so, it appears that in Tasmania the megafauna died out about 41,000 years ago. This was either before the arrival of humans (a possible arrival date being 37,000 BP) or, if it was after the arrival of humans then fire was not a factor, suggesting climate as a major cause.[7] Kohen in 1995 noted the paucity of hard geological evidence for both the hunting of megafauna and the Aboriginal use of fire in the Pleistosene and early Holocene, it seeming that improved dating techniques and significantly more data are needed to provide compelling evidence.[12]

Of the 50 species of megafauna that became extinct includes reptiles, birds and mammals. Flannery lists 41 mammalian species that became extinct at the end of the Pleistocene.[10] There were only three carnivores, a marsupial ‘lion’ (Thylacoleo carnifex), a giant lizard Megalania), and the Tasmanian ‘tiger’ (Thylacinus): as their prey was fairly lumbering, they did not need to be fast and agile like their African equivalents.

When human occupation can be clearly dated the connection between extinction and human activity is readily assessed. Maoris hunted the Moa to extinction within 300-400 years of their arrival. In Madagascar local lemuroids were extinct by about 1200 AD and the famous tame Dodo on Mauritius and Reunion was easy game for European settlers with their guns and feral pigs that would eat their eggs, the last one dated to 1681. In both North and South America with the comparatively late arrival of humans between 10,000– 20,000 BP human hunting, it appears, took only 1,000 years to target the giant herbivores, their carnivorous predators and the associated scavengers, while small animals survived. Those animals becoming extinct included mammoths, mastodons, ground sloths, horses (horses used by native Indians were later European introductions) and camels and many other animal ‘giants’.[14]

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