Two Tasmanian tigers in Hobart Zoo prior to 1921. Photographer unknown.
The Thylacine Myth
MARIE ATTARD & STEPHEN WROE
A new study of the biomechanics of the Tasmanian tiger’s skull debunks the hysteria behind the
campaign that led to its extinction.
hey were one of Australia’s great biological
mysteries, a biscuit-coloured marsupial with a
large head, bold dark stripes down its back and
a reverse-facing pouch. To newly arrived European settlers, this elusive New World creature
was a Tasmanian oddity that inevitably became a source of
confusion, contempt and fear. Now, 75 years after the last
known individual died in captivity at Hobart Zoo, the
thylacine – or Tasmanian tiger – remains one of the leastunderstood of Australia’s native animals.
But modern research is beginning to lift the veil and reveal
the tiger’s true nature. In our laboratory, for instance, advanced
computer modelling of the Tasmanian tiger’s skull suggests
that it was not well-adapted to tackle large prey. Its skull was
big but lightly constructed, and more suitable for tackling wallabies and bandicoots.
Isotope-based research is beginning to provide direct evidence
of the Tasmanian tiger’s diet. Such techniques will also help
T
to gain a more thorough understanding of diet and lifestyle in
increasingly rare Australian species.
The fossil history of Tasmanian tigers in Australasia dates
back some 23 million years, and has revealed surprising diversity. Twelve fossil species from this family are now known.
The lineage was wiped out from mainland Australia around
3000 years ago, and possibly earlier in New Guinea. Aboriginal land use patterns, climate change and competition with
dingoes have been linked to the Tasmanian tiger’s extinction
on the continent's mainland. A small population of Tasmanian
tigers persisted on the remote island of Tasmania, where there
were no dingoes and Aboriginal land use differed from the
mainland. They were by far the largest marsupial carnivore to
survive up to recent times.
Over the past decade, scientists have tried to recover DNA
from a preserved Tasmanian tiger pup in the hope of one day
resurrecting the species. Some people are even convinced that
they still exist, and extensive expeditions have sought to find
JUNE 2012 |
| 19
A large yawn from a captive Tasmanian tiger reveals its wide
jaws. The image is from a 1933 film taken by naturalist David
Fleay at Hobart Zoo. It is the last known motion picture footage
of a living Tasmanian tiger.
recent traces of this near-mythical marsupial. This almost fabled
figure ranks alongside the Loch Ness Monster and Bigfoot
among cryptozoologists – but unlike these, of course, we know
that Tasmanian tigers did exist.
A Tragic History
Tasmanian tigers were rarely sighted by early Europeans, so
contemporary accounts of their behaviour are a mix of hearsay,
fact and myth that remain difficult to tease apart. It was known
by many names – Tasmanian wolf, opossum hyaena and tiger
to name a few. Their close resemblance to other apex predators such as wolves fuelled assumptions that they were dangerous,
and aroused the fear of settlers.
Marsupials such as the Tasmanian tiger were believed to be
inferior to their placental counterparts and were seen as primitive dying races. Sir Ray Lankester, a well-known British zoologist, said: “When one watches the Tasmanian wolf, one comes
to the conclusion that it is stupid and of much lower intelligence
than the common wolf. Its appearance, ways and movements
suggest the fancy that it is a kangaroo masquerading as a wolf,
and not very successfully.”
20 |
| JUNE 2012
During the 20th century, rumours spread that Tasmanian
tigers fed like blood-sucking vampires, giving this nocturnal
predator an almost supernatural status. Similar speculation
plagued the placental grey wolf around the same time in the
United States, with such hysteria further provoking campaigns
to be rid of both species. These attitudes unwittingly shaped
settlers’ regard of the Tasmanian tiger – and likely swayed political decisions to determine their fate.
Despite their rarity, from the start the species was increasingly blamed for attacks on sheep. In an attempt to reduce the
alleged threat of Tasmanian tigers to the sheep industry, bounties were paid by land owners and farmers from as early as 1830.
Although people ultimately identified feral dogs as the more
serious and pressing menace, the media continued to depict
the Tasmanian tiger as a villain. In the 1880s Hobart’s The
Mercury newspaper described the public perception of the
animal as “cowardly, as stealing down on the sheep at night
and wantonly killing many more than it could eat, as being
worthless for its skin”.
Concerns were raised by The Mercury in 1886 about misconceptions and misinformation surrounding the so-called “tiger”:
“It is not the ferocious brute the name implies, and under no
circumstances would it attack even a child. On two occasions
I have met with recently arrived immigrants who objected to
leave town to secure work in the country for fear they or their
children might be devoured.”
In 1888 the Tasmanian government paid a pound sterling
for every dead adult Tasmanian tiger head. At the time, the
award would have been equivalent to half a week’s wage. In all
they paid out 2184 bounties, but many more were likely killed
than was claimed in the bounty records.
An epidemic disease ruthlessly swept across the Tasmanian
tiger population in the late 1800s, causing further devastation.
The Tasmanian tiger preferred open forests and heathlands
but persistent hunting and land clearing confined the fastdwindling population to dense rainforests.
Despite its obvious decline, the species did not receive official protection from the Tasmanian government until 2 months
before the last known captive animal died in 1936. Too little
was done to protect them. In the end we were too late to save
them.
Changing Perceptions
Our perceptions about the Tasmanian tiger continue to evolve
as we learn more about their behaviour through new scientific
approaches. Recent scientific findings have added to a complex
picture of how the Tasmanian tiger lived and why it went
extinct after millions of years of successful survival in Australia.
Whether or not Tasmanian tigers were capable of taking
down large prey like kangaroos, emus or adult sheep has been
Based on an analysis of
the Tasmanian tiger’s
elbow structure they
predicted that the
hunting strategy of
Tasmanian tigers more
closely resembled cats
than dogs.
A finite element model of a thylacine skull (left) and results showing mechanical stresses
placed on the skull when tackling prey (right). Blue colours represent the least-stressed
regions and red and white show the most-stressed parts of the skull. Credit: Marie Attard
a contentious issue. To answer this question requires further knowledge about
the mechanical limitations of their skull.
For this, our research team from the
University of NSW has recently analysed
the mechanical performance of the
Tasmanian tiger’s skull relative to two
living marsupial predators – the
Tasmanian devil and spotted-tailed quoll.
In the past, 2D modelling routinely
formed the basis of studies to establish
relationships between form and function
in biological structures. With exponential progress in computer hardware and
the development of new software and
protocols, we are now able to create more
realistic simulations using 3D models.
The process we apply is called finite
element analysis, which was originally
developed for the aerospace industry but
has increasingly been used to predict
the mechanical behaviour of biological
structures.
The first step is to scan a skull from
each species using CT, which stitches
together many X-ray images to create a
3D digital representation of the skull.
The material properties of bone are then
assigned to the model.
Reliable results depend on getting
accurate predictions of the forces that
would have been applied by the animal in
life. For fossil species, dissections from
related living species provide a guide to
where the jaw-closing muscles attached to
the skull.
The model we generate from this
process is used to simulate different bites
and generate predictions of how stress
and strain would be distributed through
the skull under different feeding or biting
behaviours observed in living carnivore
species.
For example, when a predator bites
down on prey it obviously uses its jaw
muscles, but killing and dismembering
prey may also include “thrashing” and
“ripping” behaviours in which the predator shakes its head sideways to rip the
prey apart. Other predators will twist
their head or, alternatively, pull backwards against the prey using their neck.
We have simulated these behaviours
for each marsupial carnivore in our study
to see how they compare.
From the results of the finite element
analysis we can assess the magnitude and
distribution of stresses in a skull in
response to biting down on or resisting
struggling prey. The colour images created
of the skull highlight areas in cool-blue
where stresses are low and hot-red to
white where stresses are relatively high.
We were surprised to find that the
Tasmanian tiger’s skull had more stress
“hot spot” zones than other large marsupial carnivores like the Tasmanian devil
and spotted-tailed quoll, which hunt
animals larger than themselves. Our
results suggest that, in contrast, the jaws
of the Tasmanian tiger were probably
better suited to catching small- to
medium-sized animals such as bandicoots,
wallabies and possums.
Most accounts from the 19th and early
20th century describe Tasmanian tigers
as solitary hunters, although they may
have hunted in small groups. This may
have consisted of two adults or a mated
pair with up to four young. With the
rapid decrease in the Tasmanian tiger
population as a result of hunting by Europeans, accounts of group hunting became
rare. The limitation of only catching small
prey by solitary Tasmanian tigers may
have placed additional pressure on this
large carnivore.
The diet of Tasmanian tigers likely
overlapped with that of the Tasmanian
devil and spotted-tailed quoll, leaving it
vulnerable to competition. Moreover,
the morphology of the Tasmanian tiger’s
teeth suggests that it was almost entirely
JUNE 2012 |
| 21
Marie Attard is using 3D modelling and analysis of stable isotopes in preserved tissues
to investigate the diet of the extinct Tasmanian tiger. Credit: Christopher Hammang
restricted to eating meat, further
restricting its ability to adapt to changing
circumstances. Limited prey options
potentially increased their susceptibility
to ecosystem disruptions, such as those
caused by European land use practices.
To provide further clues about the
Tasmanian tiger’s likely hunting style,
Borja Figueirido and Christine Janis of
Brown University have taken a closer
look at the anatomy of the elbow joint.
Based on an analysis of the Tasmanian
tiger’s elbow structure they predicted that
the hunting strategy of Tasmanian tigers
more closely resembled cats than dogs.
Cats and Tasmanian tigers both have
more flexible elbows to better manipulate and grapple with prey, features typical
of short distance ambush predators.
In contrast the elbow joint of wolves
are far less flexible, being more fixed in a
“palm” down position, making them
more effective long distance runners that
exhausted their prey.
The seemingly disproportionate and
even stumpy legs of the Tasmanian tiger
do not appear to be suitable to long
distance pursuit.
Other short-legged marsupial carnivores typically use short pursuits to
capture prey. For example, the stocky
22 |
| JUNE 2012
Tasmanian devil will use a combination
of ambush and short, moderate-speed
pursuits when hunting.
However, some historical accounts
do describe Tasmanian tigers doggedly
following prey for long periods of
time.
To really flesh out the diet of this
extinct carnivore, we are presently
analysing the chemical components of
Tasmanian tiger pelts, skulls and skeletons in collaboration with Tracey Rogers’
lab at the University of NSW. The
supporting idea is that your body tissues
originate from the food you eat. The
stable isotope signature of the food
becomes assimilated into your body
tissues, giving you a very distinctive signature of what you have been eating. Basically, you are what you eat.
To retrace the diet of a predator, we
also need to know the isotopic values of
potential prey species. In collaboration
with 20 museums worldwide we have
collected tissues from Tasmanian tigers
and potential prey species dating as far
back as the 1830s. By comparing
preserved tissue from both predator and
potential prey species, we will be able to
get a better picture of what Tasmanian
tigers were really hunting.
New Beginnings
What role does research have in shaping
our perception of the species?
Since the extinction of the Tasmanian
tiger there has been a new wave of understanding of their behaviour. We have
come a long way from the closed views
of past centuries. Research can show us
the way forward with improved and more
informed conservation strategies, but
strategies are meaningless without action
and the resources needed to put them
into effect.
Much of the Australian fauna is now
imperilled, and Australia has the very
dubious distinction of having achieved
the world’s highest mammalian extinction rate. For example, grave fears are
held that Christmas Island’s pipistrelle
bats may now be extinct, with no sightings of the species since 2009.
Tasmanian devils may be facing a
similar fate. An aggressive facial tumour
has wiped out more than 90% of
Tasmanian devils in high-density areas,
and the disease continues to spread. The
recent introduction of the red fox places
this Tasmanian icon under further pressure.
The list of Australian mammals in
danger of extinction continues – with
several species of wombats, bandicoots,
wallabies, quolls and two whales – the
blue whale and southern right whale –
at risk of extinction. Without awareness
of these issues, and even more importantly action, we may lose much of the
precious diversity our country has to offer.
What can we do to help? There are
many volunteer programs available
through organisations such as WIRES,
WWF and Australian zoos and fauna
parks. These organisations also accept
donations towards conservation.
You can make a difference to conserve
Australia’s unique wildlife.
Marie Attard is a postgraduate student studying the diet
of Tasmanian tigers at the University of NSW School of
Biological, Earth and Environmental Sciences, where
Stephen Wroe is a Senior Research Fellow and the director
of the Computational Biomechanics Research Group.