We see the surface of the sea: the rock pools, the waves, the horizon. But there is so much more going on underneath, hidden from view.
The sea’s surface conceals human impact as well. Today, I am writing a eulogy to the Derwent River Seastar (or starfish), that formerly inhabited the shores near the Tasman Bridge in Hobart, Tasmania. It is Australia’s first documented marine animal extinction and one of the few recorded anywhere in the world.
The Derwent River Seastar, preserved in the Tasmanian Museum and Art Gallery, Hobart. Credit: Christy Hipsley, Museums Victoria/University of Melbourne
Scientists only knew the Derwent River Seastar for about 25 years. It was first described in 1969 by Alan Dartnall, a former curator of the Tasmanian Museum and Art Gallery. It was found on and off until the early 1990s but scientists noted a decline in numbers. Targeted surveys in 1993 and 2010 failed to find a single individual.
It was listed as critically endangered by the Tasmanian and Australian governments. But now, like a long-lost missing person, it is time to call it: the Derwent River Seastar appears extinct.
It is actually quite hard to document the extinction of marine animals. There is always hope that it will turn up in some unusual spot, somewhere in that hidden world. Australia has an ambitious plan to create high-resolution maps of 50% of our marine environment by 2025. This is a formidable task. But it is a reflection of our lack of knowledge about the oceans that, 20 years after the launch of Google Maps and despite an enormous effort in the interim, much of Australia’s seafloor in 2025 will be still largely known from the occasional 19th-century depth sounding, or imprecise gravity measurements from satellites.
We do notice when big animals go. There used to be a gigantic dugong-like creature called Steller’s Sea Cow, which lived in the North Pacific Ocean until it was hunted to oblivion by 1768. There is no mistaking that loss.
But the vast majority of the estimated 1 million to 2 million marine animals are invertebrates, animals without backbones such as shells, crabs, corals and seastars. We just don’t monitor those enough to observe their decline.
We noticed the Derwent River Seastar because it was only found at a few sites near a major city. Its story is intertwined with the usual developments that happen near many large ports. The Derwent River became silty and was at times heavily polluted by industrial and residential waste. The construction of the Tasman Bridge in the early 1960s cannot have helped.
The Derwent River Seastar has been a bit of an enigma. From the start, it was mistakenly classified as belonging to group of seastars (poranids) otherwise known from deep or polar habitats. Some people wondered whether it was an introduced species as well, one that couldn’t cope with the Derwent environment.
However, we used a CT scanner at the School of Earth Sciences, University of Melbourne, to look at the internal skeleton of one of the few museum specimens. Sure enough, it has internal struts to strengthen the body, which are characteristic of a different group of seastars (asterinids) that have adapted to coastal environments and are sometimes restricted to very small areas.
CT scan showing the internal structure of the seastar. Source: Christy Hipsley, Museums Victoria/University of Melbourne
Is this seastar like a canary in a coal mine, a warning of a wave of marine extinctions? Sea levels are rising with global warming, and that is going to be a big problem for life adapted to living along the shoreline. Mangroves, salt marsh, seagrass beds, mud flats, beaches and rock platforms only form at specific water depths. They are going to need to follow rising sea levels and reform higher up the shoreline.
Coastal life can take hundreds to thousands of years to adjust to these sorts of changes. But in many places we don’t have a natural environment anymore. Humans will increasingly protect coastal property by building seawalls and other infrastructure, especially around towns and bays. This will mean far less space for marine animals and plants.
We need to start planning new places for our shore life to go – areas they can migrate to with rising sea levels. Otherwise, the Derwent River Seastar won’t be the last human-induced extinction from these environments.
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.
On 1 July 1983, in a dramatic four-three decision, the High Court of Australia ruled to stop the damming of the Franklin River. It brought an end to a protracted campaign that had helped bring down two state premiers and a prime minister, as well as overseeing the rise of a new figure on the political landscape – the future founder of the Greens, Bob Brown.
The fact that a remote corner of southwest Tasmania became the centre of national debate reflects what was at stake in the campaigns against hydro-electric development. For many, like novelist James McQueen, the Franklin was “not just a river”: “it is the epitome of all the lost forests, all the submerged lakes, all the tamed rivers, all the extinguished species”. The campaign was a fight for the survival of “a corner of Australia untouched by man”; it was a fight for the right of “wilderness” to exist.
“It is a wild and wondrous thing,” Bob Brown wrote of the Franklin River in May 1978, “and 175 years after Tasmania’s first European settlement, the Franklin remains much as it was before man – black or white – came to its precincts.”
But it was not only the idea of “wilderness” – of an ancient, pure, timeless landscape – that saved the Franklin. The archaeological research that took place during the campaign was at the heart of the High Court decision. Far from being untouched and pristine, southwest Tasmania had a deep human history. What was undoubtedly a natural wonder was also a cultural landscape.
‘A sea of stone artefacts’
The archaeological site at the centre of the campaign was, for a time, known by two names: Fraser Cave and Kutikina. Kevin Kiernan, a caver and the first director of the Tasmanian Wilderness Society, was the first to rediscover the site. He and Greg Middleton recorded it on 13 January 1977 as part of a systematic survey of the lower and middle Gordon and Franklin Rivers.
They were aware that the monolithic Hydro-Electric Commission was considering the region as the site for a new dam and they were searching for something – “maybe a big whizz-bang cave” – that might save these valleys from being flooded. In an attempt to raise awareness of this threatened landscape, they started a tradition of naming rock features in the southwest “after the political figures who would decide their fate”.
Fraser Cave was thus named after the sitting Prime Minister, Malcolm Fraser. There was also a Whitlam cave, a Hayden Cave and a Bingham Arch. When the Tasmanian Nomenclature Board caught wind of this tradition, they accused Kiernan and other members of the Sydney Speleological Society of “gross impertinence” for naming caves outside their state. In mid-1982, at the suggestion of the Tasmanian Aboriginal Centre, Fraser Cave became Kutikina, which means “spirit” in the oral tradition nurtured by the dispossessed Tasmanian Aboriginal community on Babel Island in Bass Strait.
But although Kiernan admired the natural splendour of Kutikina in 1977, he did not immediately recognise the artefacts it contained as human-made. It was not until he returned in February 1981 that he realised what he had found. He and the new director of the Tasmanian Wilderness Society, Bob Brown, and its secretary, Bob Burton, were searching the remote valley for evidence of a convict who had supposedly perished in the region after escaping the Macquarie Harbour Penal Station.
The story conjured the “wildness” of the country and the discovery of his bones might help bring publicity to their campaign against the dam. But when they climbed through the entrance of Kutikina, they were amazed to find a sea of stone artefacts and ashy hearths extending into the dark. These were no convict bones.
Three weeks later, a team of archaeologists, cavers and National Parks officers rafted down the Franklin River to investigate. It was already dark on 9 March 1981 when they tied their boats to the riverbank. They had a deep chill after hours navigating the fast-flowing river, hauling their aluminium punt and rubber dingy over successive rapids, journeying deeper into the dense rainforest. The rain picked up again as they unloaded their gear and took shelter in the mouth of the cave, which opened “like a huge, curved shell”.
Some of the team started a small, smoky fire to cook their dinner, while the others, with the light of their torches, ventured into the cavern. Kutikina opened out “like an aircraft hangar” and extended for almost 200 metres into the cliff. But it was not its scale that excited them: it was the idea that this remote cave, buried in thick “horizontal” rainforest, could have once been home to a thriving human population.
Too tired to erect their tents, they unrolled their sleeping mats on the disturbed floor at the cave entrance. It later occurred to them that they were probably the first people to sleep there in around 15,000 years.
Over the following days, as rain poured outside, the team carefully surveyed Kutikina. The archaeologists, Rhys Jones and Don Ranson, opened a small trench where the black sediment of the floor was covered by a thin layer of soft stalagmite. The test pit only extended to a depth of 1.2 metres before it met bedrock, but it yielded an extraordinary 75,000 artefacts and 250,000 animal bone fragments.
This small pit represented about one per cent of the artefact-bearing deposit, making the cave one of the richest archaeological sites in Australia. “In terms of the number of stone tools,” Jones said to one journalist, “much, much richer than Mungo.”
The archaeological remains at Kutikina told a remarkable story. The tools appeared to be a regional variant of the “Australian core tool and scraper tradition”, found across the mainland during the Pleistocene, suggesting immense chains of cultural connection before the creation of Bass Strait. The bone fragments were also curious. Most had been charred or smashed to extract marrow, and almost all (95 per cent) were wallaby bones, suggesting a finely targeted hunting strategy, similar to that found in the Dordogne region in France.
But most surprisingly, underneath the upper layer of hearths, there were angular fragments of limestone that appeared to have shattered and fallen from the cave roof at a time of extreme cold, forming rubble on the floor. It was one of the main pieces of evidence that led Jones to speculate in his diary: “Is this the late glacial technology?”
Home to the southernmost humans on earth
The possibility of Ice Age dates conjured the image of a dramatically different world. Pollen records in the region revealed that what is now rainforest was once an alpine herbfield like the tundra found in Alaska, northern Russia and northern Canada. Twenty thousand years ago, the mighty trees of ancient Gondwanaland had retreated to the river gorges, where they were irrigated and sheltered from fire, while wallabies and wombats roamed the high, open plains above.
The cold blast of Antarctica, only 1000 kilometres to the south, had dropped temperatures by around 6.5 degrees Celsius. A 65-square-kilometre ice cap presided over the central Tasmanian plateau, feeding a 12-kilometre-long glacier that gripped the upper Franklin valley. Icebergs floated off the Tasmanian coast.
At the height of the last Ice Age, Kutikina was home to the southernmost humans on earth. The people of southwest Tasmania hunted red-necked wallabies on the broad open slopes of Franklin valley, they collected fine stone from glacial melt water gravels and chipped them into tools, and they sheltered beside fires in the mouths of deep, limestone caverns. “They alone,” Jones reflected, “may have experienced the high latitude, glacier-edge conditions of a southern Ice Age.”
Significantly, during a separate excavation near the confluence of the Denison and Gordon Rivers, archaeologists also discovered tools and charcoal dating to 250–450 years ago, long after the ice cap had melted and the rainforest had returned. It revealed that the river valleys of southwest Tasmania had a recent, as well as a deep, Aboriginal history.
The rediscovery of Kutikina made the front page of the local and national newspapers, and was discussed on the floor of Parliament, but, surprisingly, it was restricted to the margins of the conservation campaign. John Mulvaney later reflected on the productive, albeit tense alliance between archaeologists and conservationists during the campaign:
We claimed an Ice Age environment of tundra-like grasslands, where their dearly loved primeval forest was supposed to have stood eternally. By discrediting the image of a forest wilderness, we were ruining their image and battle cry!
Added to this tension was the animosity the Tasmanian Aboriginal community felt towards both the archaeologists, for fossicking on their land, and the conservationists, for suggesting they had never lived there. Their activism during the campaign had profound implications for the Australian archaeological community. But while Aboriginal leaders such as Rosalind Langford and Michael Mansell were eager to regain control of Kutikina – “the most sacred thing in the state” – they also recognised the value of the history that had been uncovered. As Mansell said:
The fact that the Aborigines could survive physically and culturally in adverse conditions and over such a long period of time … helps me counteract the feeling of racial inferiority and enables me to demonstrate within the wider community that I and my people are the equal of other members of the community.
At the 1981 Tasmanian Power Referendum, 47 per cent of the electorate voted in favour of the Gordon-below-Franklin dam. But, remarkably, there was also a 45 per cent informal vote. Tens of thousands of voters had scrawled “no dams” on their ballot papers. The unprecedented “write-in” had been organised by the Tasmanian Wilderness Society, led by Brown. It repeated this highly organised, campaign-oriented strategy at local, state and federal elections throughout 1982.
The federal leader of the Australian Democrats, Don Chipp, also recognised the mood of the electorate against the dam and in August 1981 he initiated a Senate inquiry into “the federal responsibility in assisting Tasmania to preserve its wilderness areas of national and international importance”. Jones, Mulvaney and the executive of the Australian Archaeological Association were among the many to make submissions to the new Senate Select Committee.
The Tasmanian Aboriginal Centre also made a submission, drawing upon the archaeological research to underline the cave’s “great historical importance”. But they also made a more personal plea. The Franklin River caves “form part of us – we are of them and they of us. Their destruction represents a part destruction of us.”
This advocacy had a profound influence. Several members of the Senate Committee flew into the Franklin valley to see the ongoing archaeological work and when the committee presented its report on the Future Demand and Supply of Electricity for Tasmania and Other Matters, the archaeology dominated the “other matters”. “Apart from any other reasons for preserving the area,” they concluded, “the caves are of such importance that the Franklin River be not inundated.”
Prime Minister Fraser heeded the conclusions of the report. He did not want the Franklin dam built, but he was reluctant to intervene in what he regarded as a state matter. So he did not act when construction on the dam began in July 1982.
Protests and political shifts
On 14 December 1982, the same day the region was formally listed as a World Heritage site for its natural and cultural value, a chain of rubber rafts blocked the main landing sites along the Franklin River, protestors occupied the dam site and rallies were held in cities across Australia.
By autumn 1983, 1272 protestors had been arrested during the Franklin blockade, and nearly 450 had done time in Hobart’s Risdon Prison, including Mansell and Langford, who were charged with trespass on their return from visiting Kutikina.
While the blockade continued, and with a federal election just around the corner, the ALP made a snap change in its leadership on 3 February 1983. It replaced Bill Hayden, who had voted against Labor’s policy to stop the dam at the party’s national conference, with Bob Hawke, who had voted for it. And in a tumultuous few hours of Australian political history, Fraser called an early election on the same day. It would turn out to be a grievous political miscalculation.
Neither Fraser nor Hawke believed the Franklin River dispute decided the 5 March 1983 election, but the outgoing Deputy Prime Minister, Doug Anthony, was adamant: “There is no doubt that the dam was the issue that lost the government the election.”
On 31 March the new Hawke government passed regulations to prevent further construction on the Franklin dam. Tasmanian Premier Robin Gray took the matter to the High Court, challenging the constitutionality of Hawke’s “interventionist” legislation. His appeal failed by the narrowest of margins.
The judges in the majority considered that the Commonwealth had a clear obligation to use its External Affairs power to stop the proposed dam, as the inundation of “the Franklin River, including Kutikina Cave and Deena Reena Cave”, would breach the World Heritage Properties Conservation Act and damage Australia’s international standing. They also invoked the Commonwealth power to make laws with respect to Aboriginal people.
The Franklin River campaign has entered “the folklore of Australian environmentalism” as a green victory: a battle won, in Clive Hamilton’s words, through “the intrinsic worth of wild places.” But behind the scenes it was the deep Aboriginal history of the region that pushed the decision over the line. The archaeological evidence featured in every report about the judgement, and privately Malcolm Fraser considered it to be the deciding factor.
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.