Until it was hunted to extinction, the thylacine – also known as the Tasmanian tiger or Tasmanian wolf – was the world’s largest marsupial predator. However, our new research shows it was in fact only about half as large as previously thought. So perhaps it wasn’t such a big bad wolf after all.
Although the thylacine is widely known as an example of human-caused extinction, there is a lot we still don’t know about this fascinating animal. This even includes one of the most basic details: how much did the thylacine weigh?
An animal’s body mass is one of the most fundamental aspects of its biology. It affects nearly every facet of its biology, from biochemical and metabolic processes, reproduction, growth, and development, through to where the animal can live and how it moves.
For meat-eating predators, body mass also determines what the animal eats – or more specifically, how much it has to eat at each meal.
Catching and eating other animals is hard work, so a predator has to weigh the costs carefully against the benefits. Small predators have low hunting costs – moving around, hunting, and killing small prey doesn’t cost much energy, so they can afford to nibble on small animals here and there. But for bigger predators, the stakes are higher.
Almost all large predators – those weighing at least 21 kilograms – focus their efforts on prey at least half their own body size, getting more bang for the buck. In contrast, small predators below 14.5 kg almost always catch prey much smaller than half their own size. Those in between typically take prey less than half their size, but sometimes switch to a larger meal if some easy prey is there for the taking – or if the predator is getting desperate.
The mismeasure of the thylacine
Few accurately recorded weights exist for thylacines – only four, in fact. This lack of information has made estimating their average size difficult. The most commonly used average body mass is 29.5kg, based on 19th-century newspaper accounts.
This suggests the thylacine would probably have taken relatively large prey such as wallabies, kangaroos and perhaps sheep. However, studies of thylacine skulls suggest they didn’t have strong enough skulls to capture and kill large prey, and that they would have hunted smaller animals instead.
This presented a problem: if the thylacine was as big as we thought, it shouldn’t be able to live solely on small prey. But what if we’ve had the weight wrong the whole time?
Our new research, published today in Proceedings of the Royal Society B, addresses this weighty issue. Our team travelled throughout the world to museums in Australia, the United States, the United Kingdom and Europe, and 3D-scanned 93 thylacines, including whole mounted skeletons, taxidermy mounts, and the only whole-body ethanol-preserved thylacine in the world, in Sweden.
Based on these scans, we created new equations to estimate a thylacine’s mass, based on how thick their limbs were – because their legs would have had to support their entire weight.
We also compared the results of these equations with a new method of digitally weighing 3D specimens. Based on a 3D scan of a mounted skeleton, we digitally “filled in the spaces” to estimate how much soft tissue would have been present, and then used our new formula to calculate how much this would weigh. Taxidermy mounts were easier as there was no need to infer the amount of soft tissue. The most artistic member of our team digitally sculpted lifelike thylacines around the scanned skeletons, and we weighed them, too.
Our calculations unanimously told a very different story from the 19th-century periodicals, and from the commonly used estimate. The average thylacine weighed only about 16.7 kg – not 29.5 kg.
This means the previous estimate, based on taking 19th-century periodicals at face value, was nearly 80% too large. Looking back at those old newspaper reports, many of them in retrospect have the hallmarks of “tall tales”, told to make a captured thylacine seem bigger, more impressive and more dangerous.
It was based on this suspected danger that the thylacine was hunted and trapped to extinction, with private bounties already placed on them by 1840, and government-sponsored extermination by the 1880s.
The thylacine was much smaller than previously thought, and this aligns with the smaller prey size suggested by the earlier studies. Predators below 21 kg – in which we should now include the thylacine – all tend to hunt prey smaller than half their size. The “Tasmanian wolf” probably wasn’t such a danger to Tasmanian farmers’ sheep after all.
By rewriting this fundamental aspect of their biology, we are closer to understanding the role of the thylacine in the ecosystem – and to seeing exactly what was lost when we deliberately hunted it to extinction.
On a cold, dark night in the winter of June 2017, hundreds of people gathered on the lawns of Hobart’s parliament house to join a procession that carried an effigy of a giant Tasmanian tiger (thylacine) to be ritually burnt at Macquarie Point.
In an act called “the Purging”, part of the Dark Mofo festival, participants were asked to write their “deepest darkest fears” on slips of paper and place them inside the soon-to-be incincerated thylacine’s body. This fiery ritual, a powerful cultural moment, reflects the complex emotions that gather around this extinct creature.
More than a spectacle, the Dark Mofo event can be read as a strange memorialisation of loss and a public act of Vandemonian absolution in response to the state’s deliberate role in the tiger’s extinction. It led us to ask: what remains of the thylacine and what does it mean to come face-to-face with thylacine remains in the age of mass extinction?
Numerous “sightings” – and scientific research that seeks to resurrect the thylacine – attest to our longing to bring this species back from the dead. Our research takes a different path. We want to look for the traces of the thylacine in this time of great environmental uncertainty, in which species are becoming extinct at a rate never before experienced by humans. Facing our past losses is an important project in the Anthropocene, the age defined by humanity’s impact on the earth.
We have hunted for some of the 750 thylacine specimens in museum collections scattered around the world. These are a legacy of the period when Tasmania was a British colony, and the network of global trade that connected this small island state to the centres of colonial power.
In September 2017 we went in search of some of the creatures who had made the perilous journey to the United Kingdom: the London thylacines.
An archive of bodies
In search of what remains, we visited the Natural History Museum of London, one of the premier repositories of natural science collections in the world. In the storeroom, we were able to look through a cabinet containing trays of thylacine specimens, many with their original 19th century tags attached.
Amongst these remains were the preserved skins of Tasmanian tigers as well as skulls, bones and one thylacine pup. Stuffed and sewn, with a blind eye of cotton wool, this baby in its white protective tray was the tiniest of thylacine young.
While our photographs of the visit to the museum show us smiling in the storeroom – as travelling Australians we were pleased to be there after our long journey – we were, in fact, overwhelmed with cross-currents of emotion. The palpable shock of seeing so many thylacine bodies in trays in this and several other collections was a profound recognition of loss.
Some 167 specimens of Tasmanian tigers reside in museums in the UK alone. As such, this small joey is made more poignant by the scale of what we saw. A museum visitor might see a single thylacine on display, where one body stands in for its entire species.
Yet in the storerooms of the museum we came face-to-face with the sheer volume of animal bodies that were evacuated from Tasmania. In a world where extinction is becoming all too mundane, the individual lives and deaths of these animals were palpable.
From the late-18th century, the new Antipodean colonies in Australia and New Zealand were homes for the strangest of new creatures, at least to European eyes. A furious trade began between the colonies and Europe. New animals of scientific curiosity were avidly collected and discussed at meetings of the Royal Society of Tasmania, founded in 1843.
Here, animals such as black swans, wombats, and thylacines were exhibited, examined, and circulated. The society members responded enthusiastically to requests from Europe’s elite scientists to send specimens from the colonies. In 1847, for instance, the society’s committee minutes show that members attempted to source an “impregnated Platypus or Echidna preserved in spirits. Also the brains of the Thylacinus [Tasmanian Tiger] and Dasyurus [Tasmanian Devil]”. These were to be collected for for the eminent British comparative anatomist and fossil hunter Professor Richard Owen, one of the forces behind the creation of the Natural History Museum in London.
The bodies of animals shipped from the colonies and held in museums have always been important for scientific research; they constitute vast repositories of natural heritage material of immense value. In the Anthropocene age, the value of these animal archives as arks of genetic material has become more apparent, but they are also repositories of loss.
Moreover, many collecting institutions the world over face financial difficulties and struggle to look after their collections. Some collections are deteriorating due to lack resources and staff, and this may ultimately lead to the final disappearance of the thylacine.
Dead on arrival
We visited the London Zoo Archives to find out more about the thylacines displayed there over the 19th and early-20th centuries. The London Zoo was the place to which the first and last recorded Tasmanian tigers were exported – the former in 1850 and the latter, purchased for the princely sum of 150 pounds, in 1926. The very last thylacine outside of Australia died at the London Zoo in 1931.
The long sea journey was harsh, and many of the thylacines shipped from Van Diemen’s land were simply declared “dead on arrival”. One animal died just eight days after arriving in 1888. In the hope of offspring, many thylacines were shipped in breeding pairs. Yet these hopeful reproductive futures were often foreclosed when one of them died in transit, as was the case of the final shipment in 1926.
We were lured to the London Zoo archives by the librarian’s mention of the “death books”, a remarkable set of “Registers of Death in the Menagerie.” Within these weighty volumes we found page after page of neat, looping cursive script listing the dates, names, “originating habitat”, “cause of death” and “how disposed of” for all the animals that died in the London Zoo, beginning in 1904.
As we turned the pages and moved through the years, we witnessed the deaths of the “Tasmanian wolf” amongst a veritable menagerie of animals from all over the globe and especially from Britain’s colonies – Egypt, South Africa, India, Ceylon, the west coast of Ireland, and Australia – reflecting the imperial networks of exchange and transportation through which these animals were shipped.
Among two black swans found dead within days of each other, budgerigars found “worried to death”, and a “black-faced kangaroo” that died of pneumonia in the cold, wet English weather, was the thylacine that died on January 17 1906. This was “Specimen 91”, a female purchased on March 26 two years before.
Yet while there is little information on the cause of her demise, the death books note she was “not examined” but was “disposed of” to “W Gerrard (of Gerrard and Sons taxidermist)” and “sold for 1 pound, 1 shilling.”
Armed with the 1869 plans of the zoo, we went looking for the thylacines’ cage. From the map we could see that thylacines had been kept in a far corner of the zoo, near the banks of a rivulet. Due to more recent building and development, pinpointing the exact location was a challenge. What we did find was a nondescript, brutalist building and an asphalt service road. Of the thylacine enclosure, nothing remained.
This site resonates with the abandoned Beaumaris Zoo in our home city of Hobart, the location of the “final” thylacine death, which sits on the banks of the River Derwent in Hobart behind locked gates. Both of these spaces are forgotten sites of death. They are where thylacines began and ended their journeys, places which link the colony and London through circuits of scientific trade and esteem, where animal lives and deaths were managed by bureaucratic processes, and where humans and thylacines came face-to-face. But what remains at these sites? Nothing that would tell the sad story of the thylacine.
The “last” thylacine died of exposure after it was locked out of its sleeping enclosure on September 7 1936 at Beaumaris Zoological Gardens on the Hobart Domain. This death, now so weighted with significance, went unremarked at the time. There were no news reports to record the animal’s passing and its remains were thrown away.
The extinction of the thylacine is particularly resonant because it was annihilated through human actions; its death was sanctioned by government policy and deliberately and systematically enacted.
The thylacine was demonised by Tasmanian graziers as a blood-thirsty carnivore that liked to feed on sheep. While the Van Diemen’s Land Company had placed a bounty on the head of the thylacine in 1830, it was the parliament that signed the species’ death warrant. Between 1888 and 1909 the government paid one pound per adult and ten pence per young, during which time 2,184 bounties were rewarded. The public knew what it was doing. In 1884 a group of farmers on Tasmania’s east coast set up the “Buckland and Spring Bay Tiger and Eagle Extermination Society” with the explicit purpose of eradicating the species.
The cultural guilt that attends the thylacine is perhaps why it is such an important international symbol for extinction and why the date of the death of the last thylacine is now National Threatened Species Day.
The thylacine’s legacy
The spectre of the thylacine haunts the public imagination and there is significant scientific focus on the physical remains of this now infamously extinct creature. In 2017 there was a spate of highly publicised “sightings” in Queensland and Tasmania.
Indeed, they found a mix up: some specimens were tiny quolls or Tasmanian devils, not thylacine joeys at all. As an article in The Guardian noted, the research “all contributes to the ultimate end goal of bringing back a thylacine, a project that is technologically distant but theoretically possible.”
However, for scholars Thom van Dooren and Deborah Bird Rose, de-extinction projects blind us to the finality of extinction. They advocate actively grieving extinction because it does important political work. They write: “The reality is that there is no avoiding the necessity of the difficult cultural work of reflection and mourning. This work is not opposed to practical action, rather it is the foundation of any sustainable and informed response.”
Australia has the worst mammal extinction rate in the world. The thylacine is one of 30 mammals that have been lost here since European settlement. Thinking through the meanings and politics of the loss of the thylacine is crucially important in this context. Rare thylacine remains, housed in museum collections around the world, are precious archives that are part of our global heritage. We must take care of them. Moreover, facing this loss directly in the age of extinction is a political act.
This collaborative interdisciplinary project, “Extinction Afterlives”, brings together Associate Professor Penny Edmonds, Dr Hannah Stark and Adjunct Associate Professor Katrina Schlunke, University of Tasmania, to consider the cultural life of the extinct thylacine and other creatures in the Anthropocene.
We wish to thank Roberto Portela Miguez, Senior Curator in Charge of Mammals, The Natural History Museum, London, for hosting our visit to the museum and for his helpful discussions on this essay topic. Also, Mathew Lowe, Collections Manager, University Museum of Zoology, Cambridge University, Kathryn Medlock, Senior Curator Vertebrate Zoology, Tasmanian Museum and Art Gallery, and Tammy Gordon, Collections Officer, Natural Sciences, Queen Victoria Museum and Art Gallery, Tasmania.
There’s no doubt that humans killed off the Tasmanian tiger. But a new genetic analysis suggests this species had been on the decline for millennia before humans arrived to drive them to extinction.
The Tasmanian tiger, also known as the thylacine, was unique. It was the largest marsupial predator that survived into recent times. Sadly it was hunted to extinction in the wild, and the last known Tasmanian tiger died in captivity in 1936.
In a paper published in Nature Ecology and Evolution today, my colleagues and I piece together its entire genetic sequence for the first time. It tells us that thylacines’ genetic health had been declining for many millennia before they first encountered human hunters.
Our research also offered the chance to study the origins of the similarity in body shape between the thylacine and dogs. The two are almost identical, despite having last shared a common ancestor more than 160 million years ago – a remarkable example of so-called “convergent evolution”.
Decoding the thylacine genome allowed us to ask the question: if two animals develop an identical body shape, do they also show identical changes in their DNA?
These questions were previously difficult to answer. The age and storage conditions of existing specimens meant that most thylacine specimens have DNA that is highly fragmented into very short segments, which are not suitable for piecing together the entire genome.
We identified a 109-year-old specimen of a young pouch thylacine in the Museums Victoria collection, which had much more intact DNA than other specimens. This gave us enough pieces to put together the entire jigsaw of its genetic makeup.
Next, we made a detailed comparison of thylacines and dogs to see just how similar they really are. We used digital imaging to compare the thylacine’s skull shape to many other mammals, and found that the thylacine was indeed very similar to various types of dog (especially the wolf and red fox), and quite different from its closest living marsupial relatives such as the numbat, Tasmanian devil, and kangaroos.
Our results confirmed that thylacines and dogs really are the best example of convergent evolution between two distantly related mammal species ever described.
We next asked whether this similarity in body form is reflected by similarity in the genes. To do this, we compared the DNA sequences of thylacine genes with those of dogs and other animals too.
While we found many similarities between thylacines’ and dogs’ genes, they were not significantly more similar than the same genes from other animals with different body shapes, such as Tasmanian devils and cows.
We therefore concluded that whatever the reason why thylacines and dogs’ skulls are so similarly shaped, it is not because evolution is driving their gene sequences to be the same.
The thylacine genome also allowed us to deduce its precise position in the marsupial family tree, which has been a controversial topic.
Our analyses showed that the thylacine was at the root of a group called the Dasyuromorphia, which also includes the numbat and Tasmanian devil.
By examining the amount of diversity present in the single thylacine genome, we were able to estimate its effective population size during past millennia. This demographic analysis revealed extremely low genetic diversity, suggesting that if we hadn’t hunted them into extinction the population would be in very poor genetic health, just like today’s Tasmanian devils.
The less diversity you have in your genome, the more susceptible you are to disease, which might be why devils have contracted the facial tumour virus, and certainly why it has been so easily spread. The thylacine would have been at a similar risk of contracting devastating diseases.
This loss in population diversity was previously thought to have occurred as a population of thylacines (and devils) became isolated on Tasmania some 15,000 years ago, when the land bridge closed between it and the mainland.
But our analysis suggests that the process actually began much earlier – between 70,000 and 120,000 years ago. This suggests that both the devil and thylacine populations already had very poor genetic health long before the land bridge closed.
Now that we know the whole genome of the Tasmanian tiger, we know much more about this extinct animal and the unique place it held in Australia’s marsupial family tree. We are expanding our analyses of the genome to determine how it came to look so similar to the dog, and to continue to learn more about the genetics of this unique marsupial apex predator.