In the Top End of Australia’s Northern Territory
there’s a rugged area that today is called
Arnhem Land, and it’s the homeland of a
number of the continent’s Aboriginal groups.
It’s full of rocky outcrops that sheltered
the first people to reach Australia many thousands
of years ago.
And they left a fascinating record of drawings
on the rock faces there.
This place has more rock art than anywhere
else in Australia. Peek inside any outcrop
and you may find hundreds or thousands of
drawings layered on top of each other, creating
a rich visual history of human habitation.
Some of these drawings depict animals that
are still around today, like turtles and kangaroos.
More recent drawings include animals that
were introduced to Australia, like dingos
and horses.
But beneath these layers are other drawings
of animals SO strange that, for a long time,
some anthropologists thought they could only
have been imagined.
There are enormous marsupials, giant kangaroos
with a single claw on each hindfoot, and lion-like
creatures.
But what if these animals really had existed,
after all?
What if the drawings made by the original
inhabitants of Arnhem Land were a faithful
record of the wildlife they’d actually seen
- wildlife that went extinct during the Pleistocene
epoch?
We know that fossilization is a special process
that only happens when the conditions are
just right. That means that certain environments
might not leave a fossil record.
And even when we find fossils, they can’t
always give us the full picture of what an
organism looked like.
While it’s still debated whether the drawings
truly represent extinct megafauna, they could
be a valuable source of knowledge - one that
might help expand our understanding of the
Pleistocene fossil record of Australia.
The first people to make it to Australia got
there at least 50,000 years ago, and possibly
as early as 65,000 years ago.
These original inhabitants are thought to
have arrived in boats from Asia. They established
their foothold on the continent in rock shelters
in northern Arnhem.
It’s hard to pinpoint exactly when they
began making rock art, but crayons made of
ochre, a brownish-reddish earth pigment, have
been found there that date to around 50,000
years ago.
And there are cave paintings on the Indonesian
island of Borneo that are between 52,000 and
40,000 years old, so the first people to set
foot in Australia might’ve brought a drawing
tradition with them from Asia.
The oldest drawing in Arnhem found so far
is an X-shaped pictograph made with charcoal
that scientists were able to radiocarbon-date
to around 28,000 years old. But there are
still many pictographs that haven’t been
dated.
Now, we don’t have a lot of fossil evidence
to show us what animals the first people in
Australia encountered, because Arnhem Land
has acidic soils, which don’t preserve fossils
well, as the acid can dissolve bone material.
Because of this, most animal remains found
in this area are rarely over 4000 years old.
But what we do have are the drawings, which
have provided scientists with some tantalizing
insights.
For example, at a site known as the Djulirri
rock art complex, there’s a picture that,
at first glance, was interpreted as a Thylacine
Thylacines are also called Tasmanian Tigers,
due to their striped coats, or Tasmanian Wolves
because they kinda look like wolves.
And they lived alongside people for a long
time, until they were eventually pushed to
extinction on the Australian mainland - and
when exactly that happened is still being debated.
But a more recent, closer examination of the
drawing suggested that it may actually be
of the marsupial lion –  Thylacoleo
This depiction had a long head, a short, deep
muzzle, and stout jaws, and these look more
like the anatomy of Thylacoleo than the more
delicate features of a thylacine.
The only reliably-dated Thylacoleo fossils
were found in eastern Australia, not in Arnhem
Land, with  the youngest of these dating
to 40,000 years ago.
And researchers estimate that it went extinct
around 30,000 years ago.
So, the fossil evidence shows that these marsupial
lions survived into a time where they could’ve
overlapped with people for potentially 20,000
years or more.
And if the cave drawing really represents
a Thylacoleo, it suggests that people in Arnhem
Land might’ve been familiar with this creature
- hopefully from a distance, as these predators
are thought to have been hyper-carnivores.
They were about half the size of a modern
lion, but relative to body size they have
the largest meat-slicing carnassial teeth
known and a stronger bite force than any other
mammalian carnivore.
And while we know thylacines and Thylacoleo
both existed, there are other animals in the
Arnhem Land pictures that seem to straddle
the line between imagination and reality.
Like, in another rock art complex called the
Ubirr, there’s a drawing that’s clearly
a kangaroo, but it doesn’t look like any
kangaroo alive today.
It has a shorter face with tufted fur sticking
up from its ears and a single large claw on
each back foot.
Its tail is thick along its entire length,
not tapering, like a modern kangaroo’s.
And it also has a level of anatomical accuracy
that suggests that it really existed, like
the animal’s, uh, testes hanging just below
the base of the tail.
But little attention was paid by anthropologists
to this drawing for many years. Even though
it was the biggest animal depicted on the
rock, it was obscured under layers of more
recent drawings.
Paleontologists now think it was a Procoptodon
goliah, an extinct species of short-faced
kangaroo that had a large single clawed toe
on each hind foot. And it was over two and
a half times as heavy as a modern Red Kangaroo.
Again, reliably dated fossils of this creature
have not been found in Arnhem Land. However,
fossils have been uncovered at many sites
concentrated in southeast Australia where
conditions are more conducive to fossilization.
The youngest fossils of Procoptodon goliah
are dated to 46,000 years ago. So these fossils
are young enough that this massive kangaroo
may have lived among the people of Arnhem
Land.
In fact, some Australian Aboriginal oral traditions
include accounts of a huge, aggressive kangaroo
that attacked people with its long arms.
There were a number of short-faced kangaroo
species living in Pleistocene Australia, with
jaws adapted for grinding up tough leaves.
But Procoptodon goliah was the largest of
this particular group.
And since it was at least 230 kilograms, this
mammal was probably too heavy to hop.
Instead, anatomical studies show that it was
adapted to stride, shifting its weight from
leg to leg, kind of like we do.
So, a marsupial lion with a super-bite, and
a striding attack kangaroo. What else might
the first people in Arnhem have seen and recorded
as part of their environment in Australia?! Well,
they may have also encountered the largest
marsupial to ever live!
Recent analyses by paleontologists have identified
a possible Diprotodon represented in the rock
art of Arnhem.
Diprotodon was 1.8 meters
tall at the shoulder, almost 4 meters long,
and approaching 2800 kilograms, taking the
prize for the most mega of the megafauna of
Australia as its largest mammal ever.
Like other megafauna, Diprotodon left no fossils
to prove its existence in northern Australia,
but based on the variation in the isotope
signatures of its incisors, researchers think
they migrated.
As a bulky, migratory herbivore, Diprotodon
filled the role in Pleistocene Australia that
mammoths and mastodons filled elsewhere...only
it was a marsupial.
So it’s possible the people of Arnhem Land
would’ve encountered it as it wandered across
Australia.
Diprotodon fossils suggest it went extinct
around 25,000 years ago, giving it one of
the longest overlaps with people.
So what happened to all of these odd creatures
that existed at the same time as, and maybe
even crossed paths with the first people of
Australia?
Well, Australia got a lot warmer and drier
leading up to 50,000 years ago.
Water became scarce, and inland lakes shrunk
or disappeared, changes that might have contributed
to the extinction of the megafauna. But the
exact timing of their extinction is still
an open question.
And bringing together the two lines of evidence
- art and fossils - can help us better understand
the past, especially when the fossils are
absent.
Fossils can prove that many strange creatures
that are now extinct once really did exist,
while cave paintings and rock art can help
mark their distribution over the landscape,
including in areas with poor fossil preservation.
The art may also help us understand variation
within a species, too, if it's known from
just a couple of fossils, and reveal things
like coat color and soft tissue anatomy that
usually aren’t preserved.
What is now clear, is that large creatures
lived in Australia during the Pleistocene,
and that some of them very likely overlapped
with the first people on the continent.
Today, we see the more modestly sized survivors
- like wombats, koalas, and red kangaroos
- that are still around.
But in the layers of rock art, we can see
the landscape of the past.
It’s a record that can add rich detail to
our understanding of the megafauna that once
existed, uniting traditional knowledge of
the environment with modern paleontology to
shed light on Australia’s unique megafauna.
Having a rough year? You’re not alone—we’re all trying to make sense of 2020
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