The Ancestral Australian Aborigines As a Possible Cause for the Extinction of Australia's Pleistocene Marsupial Megafauna

A few weeks ago, in my Anthropology class, we had to do a cultural profile of one culture group of humans.  I chose the Australian Aborigines and, having just finished Tim Flannery's excellent book "Chasing Kangaroos," this whole concept of the Ancestral Aborigines being the possible cause of the extinction of Australia's Pleistocene megafauna was still quite fresh in my mind, so I included it in the paper.  I thought it was pretty interesting, and so I have decided to share it with ya'll, too, with a few brief modifications to make it more Blog friendly!  Hope you enjoy, and if you want a more comprehensive look at the topic, I highly recommend "Chasing Kangaroos!"

Interestingly, paleontologists today are using the Australian Aborigines to help them figure out when Australia's Pleistocene megafauna went extinct.  While today, there are no native animals larger than the red kangaroo, Pleistocene Australia was a very different place, as was the rest of the world.  The Pleistocene Epoch was the time of the Ice Age megafauna.  With the exception of Africa and south-east Asia, in most places nowadays, the Pleistocene megafauna is extinct, but back then, the megafauna were a world-wide phenomenon.  In Eurasia, there were the giant mammoths and rhinoceroses, the cave lions and hyenas, the Irish elk, and the giant polar bear.  In North America, there were the mammoths and mastodons, the short-faced bear, the giant bison, the dire wolf, the giant beavers, and the saber-toothed cats.  In South America, there were the giant ground sloths, the armored glyptodonts, and many large relatives of elephants.  

Australia also had its fair share of Pleistocene megafauna, with marsupial lions, the giant short-faced kangaroos, the hippo-sized wombat Diprotodon, and echidnas that were the size of sheep.  There are two main hypothesis when it comes to what caused the extinction of all these animals: climate change, or hunting by early human arrivals on Australia, the first Aborigines.  No one could figure out whether it really was the Aborigines that had hunted the megafauna to extinction, though, because no one could figure out the date that the megafauna had gone extinct, nor could they figure out the date that humans first arrived on Australia.  Some people believed that the megafauna survived until around 6,000 years ago, while others believed that they went extinct a great many years prior.  The same difficulties confronted those scientists attempting to determine when humans first arrived.  The sediments of Australia are notoriously hard to date, and since the animals of Australia are so unique (especially following the extinction of the dinosaurs), scientists were unable to correlate their data with other places around the world.[1] 

As more scientific discoveries were made, a new method of dating rocks was discovered, called optically stimulated luminescence (or OSL for short).  Using OSL, paleontologists were successfully able to date many different specimens of the various marsupial Pleistocene megafauna, and found that, while many of them approached the 46,000 years ago mark, none of them passed it.  Many different specimens were used from all across Australia, but they all said the same thing: 46 was the answer. 

Meanwhile, with the new OSL tool in their bag, other scientists headed off to sites of known human habitation to attempt to date them as well, and these efforts proved to be successful.  One of the main places that they dated was a place known as Devil’s Lair, a known area of ancient Aboriginal inhabitance.  What was especially important about Devil’s Lair was that there was sediment present for the last 63,000 years, meaning that instead of just a snapshot of time, the scientists had an uninterrupted sequence of time to figure out when humans started living there.  As the scientists dated the sediments with the first signs of human inhabitance, they came up with the magic number: 46,000.  Other sites came up with the same number too, including Lake Mungo, the oldest human burial known from Australia.  At Lake Mungo, the dates were a bit less precise, ranging from between 45,000 and 47,000 years ago, but the data still seems to point in the same direction.  The ancestral Aborigines arrived on the continent at around the same time that Australia’s Pleistocene megafauna went extinct.  With this new dating technique, scientists were also able to determine that there was no significant climate change for many thousands of years on either side of the 46,000 mark, effectively ruling out that hypothesis.  So it seems that, for a time, the people who believe themselves as part of the land and the natural world around them actually destroyed a significant part of it.

[1] For example, paleontologists studying dinosaurs of the Late Jurassic Morrison Formation here in Colorado are able to look at closely related dinosaurs in other parts of the world like the UK and southern Africa (keep in mind that the continents were all together in one big landmass back then.)  That way, if the paleontologists are unable to determine the dates of, say, the Tendaguru Formation in Tanzania, they can look to the studies done on the rocks of the Morrison Formation for an accurate estimation.  This is a luxury that paleontologists, archaeologists and other scientists working in Australia simply do not have. 

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War of the Wombats

There are three different types of wombat.  There is the common wombat (Vombatus ursinus), the southern hairy-nosed (Lasiorhinus latifrons) and the northern hairy-nosed (L. krefftii).  They have been classified by the IUCN, respectively, as Least Concern, Least Concern, and Critically Endangered.  Unfortunately, all three wombats face threats that could easily result in their extermination from the wilds of the earth.  Fortunately, steps are being taken to prevent such a wombacide.

In Queensland, Australia  lies Epping Forest National Park.  In just two square miles of this park live the last ninety individuals of the northern hairy-nosed wombat.  Surrounding this puny area is a 20 kilometer long perimeter fence, erected after 10 wombats were killed by dingoes a few years ago, which, considering the severity of a ten percent population loss in such a small population, makes total sense.

Although these steps are being taken to protect the northern hairy-nosed, this species of wombat still faces several severe problems.  One such problem is the fact that 75% of these wombats are male, making a boom in their population more difficult to achieve.  Fortunately for the northerners, the southern hairy-nosed wombat has a very similar reproductive system as the northern hairy-nosed.  Scientists are therefore using female southerners as surrogate mothers for the northerners.  This method is referred to as "cross fostering," and has been used successfully when it comes to other marsupials.

The other major problem confronting the northern hairy-nosers is the fact that all of the animals are located in the same place.  In the event of a disease, wild-fire, or some other similar catastrophe, most or all of these creatures could be exterminated in the virtual blink of an eye.  Conservationists think it wise to create a second population of northerners, not too far away from the first, but far enough away to ensure that a disaster could not take out both populations with one fell swoop.  Scientists and conservationists have decided that it would be most beneficial to the northerners if they were to assist in their burrow construction.

These burrows, which can be over 100 feet long, would be time-consuming construction projects.  Not only that, but a single wombat will often use up to five different burrows, moving to a different one each day.  The first wombat doesn't just leave his or her old burrow unoccupied, however, as another wombat, probably the same one every five days or so (I would guess), temporarily moves in.  It's really less of a permanent residence, like a house, and more of a time-share condo.

But just how time and energy consuming would it be to dig such a burrow if you were a wombat?  Wombats have a problem with keeping cool.  If you ask my opinion, I suspect it has a lot to do with their body design.  As we discussed a few posts ago, animals that live in hot environments typically adapt in ways to increase their Surface Area to Volume ratio, or SA:V for short.  To learn more about why this is, click HERE.  However, fossorial, or burrowing, animals, like the wombat, aardvark, marsupial mole, and many, many others, try to keep their bodies streamlined.  Like dolphins and sharks, these animals want to be able to glide smoothly through their desired area (be it water or burrows).  Having random chunks of body, i.e. the ears of an elephant or a deer, would merely slow the animal down.  That is my theory, anyways.

To keep cool in the heat of the Australian day, wombats will take refuge in their burrows.  However, to be efficient enough when it comes to trapping moisture (as water can often be very difficult to come by in the habitat of the northerns), it has been estimated that the burrow would need to exceed fifteen feet in length.  It has also been calculated that the approximate amount of energy required for a wombat to dig a three foot long chunk of burrow is about the amount of energy that a wombat would expend running twelve miles.  That means for the comforting fifteen foot length of burrow, the wombat could instead run about sixty miles.  Clearly no small effort.

The way that the scientists actually figured all of this out was really quite interesting.  To see how long it takes for a wombat to dig a burrow, experimenters Glen Shimmin and David Taggart put one wombat into a box.  (Equipped with breathing holes, of course.  As pirates and I like to say, "A dead wombat digs no holes").  The human duo then dug a hole in the ground the same size as the box.  Placing the wombat-infested box into the ground, they then opened up one end of the container, allowing the wombat free access to the soil.  Instinctively, the wombat would begin to dig.  A half an hour later, Shimmin and Taggart ceased the wombat-excavation, and carefully measured how much dirt was displaced by the wombat, as all of the displaced dirt would conveniently be shoved (by the wombat) into the box!  Convenient, huh?  During the half hour digging session, the wombat moved more than 100 pounds of dirt!  Impressive, but the team concluded that, if conservationists were to release a group of northern hairy-nosed wombats into their new territory without pre-dug burrows, it was incredibly likely that the wombats would simply dig themselves to exhaustion, and subsequent death.  An undesirable outcome for all parties involved, it was decided to dig man-made burrows, resembling those of wombats, throughout the habitat, prior to the installation of the wombat center-piece.

What are some other problems facing wombats?  Well for starters, some of these problems, even when facing the wombats in the face, are virtually invisible to them.  Wombats, like Stegosaurus, rhinos, and myself (without my contacts), are virtually blind.  You don't need eyes if you are a fossorial (burrowing) creature; just ask the marsupial mole, the golden mole, or many other types of fossorial animals who no longer use, or even have, eyes!  However, when it comes to crossing roads, their terrible eyesight really takes its toll.  Hundreds, if not thousands, are hit by cars each year.

Other problems include starvation, drought, mange, and other people problems.  Starvation can be easily caused by the gradual squeezing out of the native grasses typically consumed by wombats by other, inedible grasses.  Drought should be self-explanatory; without water, the food dies.  Without water, there is no water.  Both are not good for wombats.  Mange, for wombats at least, is a fatal skin disease.  And as for the other people problems?  Let's just say that prairie dogs can relate.  (And now, even though I just said "Let's just say," I am going to go into more detail).  Like prairie dogs, wombats burrow.  And also like prairie dogs, the habitat of the wombat is perfect for ranchers.  So it goes like this.  Ranchers come along, and bring their cattle.  The cattle step in prairie dog/wombat holes, break their legs, and die.  The ranchers, enraged, take their rage out on the culprits: the prairie dogs or the wombats.  And as we have discussed before, wombat burrows can be quite extensive.  Furthermore, the entrance holes would have to be quite fat in order to accomodate such...robust occupants. 

As we have also previously discussed, much is being done in order to protect the wombat.  Another bit of good news is that a population boom of around 10% was recorded for the sole population of the northern hairy-nosed wombat!  Another wee bit of hope in a world that we willfully wish not to become wombatless.

WOMBAT FACTS:

1. Cooling Off:  Besides retreating into their burrows, wombats will also flick dirt onto their bodies to keep cool.
2. Olympic Runners:  Despite its dumpy appearance, the wombat can reach a top speed of around 25 mph.  This means that it can outrun an Olympic sprinter, like Usain Bolt!
3. Cooling Off V 2.0:  Besides retreating into their burrows and flicking dirt onto their bodies, wombats are also nocturnal, meaning that they avoid the heat of the day.
4. Life Span:  Wombats can live around twenty years.
5. Wombat Wesearch:  Prior to around fifteen or so years ago, not much research had been done on wombats.  Most of what we know has been discovered since that time.
6. Power House Excavators:  For their size, wombats may be the world's most powerful excavators.

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The Function of Cheek Pouches

A possible ancestor of Diprotodon (the largest mammal known from anytime in Australia, as well as the largest known marsupial known from anywhere in the world, and a relative of the wombat), the skull of Euryzygoma dunense, another extinct, megafaunal, eight foot long, quadrupedal herbivorous marsupial, is quite interesting: it has two extended cheekbones.  This gives Euryzygoma the unusual mammalian property of its skull being wider than it is long.  Although to most this probably doesn’t actually seem all that exciting, the extended cheekbones have led to two interesting theories regarding their function in the living animal.  One we will look at in a few weeks (the week of August 3rd to be more precise), but the other one we will look at now.

The hypothesis came about when the skull of Euryzygoma was first described.  The scientists who first described Euryzygoma thought that the lateral extensions of the zygomatic arch resembled those seen in squirrels, gophers and various types of Old World Monkeys, like the macaque and the baboon. 

 In the living animals just described, these lateral extensions function as cheek pouches, which make it so that the animals that possess them can store food in them.  That is why you so often see a squirrel running around with its cheeks puffed out.   

Some scientists think that Euryzygoma might have used its cheek pouches to store water; thus, it would not need to spend so much time near waterholes that were most likely infested with large crocodiles.  This would also help Euryzygoma travel longer distances during a drought, enabling it to move greater distances to reach waterholes that other animals would simply unable to reach, having a much more limited range.