little creatures like rats and mice, dunnarts and antechinuses,
along with the odd possum and bandicoot.
What is striking, though, is the sheer abundance of fossil
material. We once estimated that for every 10 litre bucket of sedi-
ment excavated from the loor of the cave, we’d have around
20,000 skeletal elements. That’s a seriously rich fossil deposit.
What we were hoping to do was look at how the small fauna
responded to climate changes during the last Ice Age, not what
happened to the megafauna.
The majority of animals that ended up in the cave were
derived from the feeding activities of prehistoric owls. The owls
typically roost in the caves during the daytime and leave to
hunt at night. It’s pretty hard for an owl to pick up a kangaroo
or wallaby, so its diet is mostly restricted to smaller critters like
rats and mice.
The owls will return to the cave with their prey and begin
to rip them apart with their talons and beak. They swallow
their food in small portions and do their best to digest it. It’s
hard for feathers, teeth and bone to pass through the digestive
system, so they are coughed back up, with the resulting owl
pellet ending up on the loor of the cave. It is those pellets, full
of the remains of small critters, that make it into the fossil
record.
About 2 years ago we were sorting through the bone frag-
ments and noticed something unusual – a very weird but unique
fossil of an animal that we were not expecting to ever ind in
Colosseum Chamber. The fossil was an osteoderm, a type of
“skin bone” that grows under the scales of lizards. Its size and
shape meant that it could only be from a massive extinct lizard:
one of the giant monitors.This specimen looks pretty boring. It’s
only around 1 cm long and resembles a
cylinder that has had its ends tapered and
then slightly twisted on the long axis. At this
size, though, it’s actually up to ive times
bigger than the equivalent osteoderm in the
second-biggest lizard alive today, the South-
East Asian water monitor. We’re not able to
say deinitively which of the extinct giant
monitors it belongs to, but it was certainly a
whopping animal.
Its input into the cave system is unlikely
to have been from an owl. Rather, it is possible
that an animal such as a quoll scavenged the
carcass of a big dead adult monitor lizard,
and dragged some skin-covered tissue into
the cave to eat it in peace. Any uneaten skin
would have subsequently decayed, leaving
the hard, boney osteoderm to survive and
become incorporated into the fossil record.
This seemingly ordinary bone told us an amazing story: not
just that it was from a giant extinct monitor lizard, but the
dating component of our investigation showed that it was just
under 50,000 years old. That meant that this cold-blooded
killer lizard overlapped in time with the earliest humans living
in Australia.Ice Age Cold Case
Over the past decade there was been enormous debate over
who or what wiped out the megafauna. It wasn’t just the pred-
ators that were big during the last Ice Age, but there was an
assorted range of giant herbivores too, including the 3000 kg
wombat-like Diprotodon, a diverse mob of massive kangaroos,
as well as huge emu-like birds and even monstrous land turtles.
All up, around 90 megafauna species suffered extinction during
this period.
Some researchers have argued strongly that humans wiped
out the megafauna, either through overhunting or perhaps via
indirect landscape modiication such as artiicially increasing the
incidence of ires. However, a close reading of the existing
datasets shows that only around 15 species of megafauna actu-
ally date to the time of humans in Australia; most of the other
75 or so species either signiicantly pre-date humans or have
no reliable ages at all.
Such was the case with the giant monitors. There have been
claims for geologically “young” lizards in archaeological contexts,
but these claims have been dismissed by the same researchers
who have argued that humans wiped out the megafauna. Para-
doxically, though, if you remove those scant records from the
existing datasets, there is no reliable evidence at all that humans22 | APRIL 2016
Microfauna collected from Colosseum Chamber. Credit: Gilbert Price