​After the geographic isolation which occurred when the land bridge was submerged beneath the Bass Strait, the common wombat diverged into three subspecies. One subspecies, Vombatus ursinus hirsutus, lives in mainland Australia. Lutruwita/Tasmania evolved two distinct subspecies. Vombatus ursinus tasmaniensis (pictured here) is found only on the island of Lutruwita/Tasmania itself. The other Tasmanian subspecies, Vombatus ursinus ursinus, evolved on Tayaritja/the Furneaux Group of Islands. It is now restricted to Flinders Island and has since been introduced to Maria Island. Photograph by Alan Dahl. CC BY-NC-ND.

Bass Strait last formed at the end of the most recent glacial period, around 12,000 years ago. Since then, several species have gone extinct either side of this barrier. Devils and thylacines famously survived into modern times in Tasmania, while the mainland Australian populations were driven extinct about three thousand years ago, most likely because of being hunted by dingoes. More recently, eastern quolls were driven extinct on the mainland in the twentieth century, this time because of human activity, including the introduction of predators like foxes and cats.

Lutruwita/Tasmania was not spared either, with European hunting and land-clearing driving the extinction of Tasmanian emu and surviving thylacine populations, while forester kangaroos only survive in part of their pre-European range. In this way, the Bassian Plain and Bass Strait seaway have played an important role in shaping biodiversity found living within this region today. However, further back in time, the Bassian Plain land bridge allowed an even larger suite of wildlife to cross what was to become Bass Strait.

During the Pleistocene, southeastern Australia was home to a diverse group of species that are today generally known as the extinct Ice Age Megafauna. This included the largest marsupial of all time, Diprotodon optatum, a giant 3,000-kilogram herbivore that would have shaped Australian ecosystems the way elephants do in modern Africa. But while Diprotodon was present in Victoria, no fossils have yet been found in Lutruwita/Tasmania, with the most southerly specimens coming from the heart of the Bassian land bridge in the muddy swamp sediments of King Island. This pattern holds true for a suite of mainland megafauna species that are unexpectedly absent from Lutruwita/Tasmania, including Propleopus, a giant rat-kangaroo, Phascolonus, a giant wombat, and Procoptodon, the biggest-ever kangaroo. This pattern may be explained by the ‘peninsula effect’. A peninsula is a narrow, isolated strip of land surrounded by sea, which is what Lutruwita/Tasmania became when the sea levels lowered to expose the Bassian Plain land bridge. Species diversity, or the number of species in an area, tends to reduce as you travel towards the tip of a peninsula.

The largest marsupials known from Lutruwita/Tasmania at that time were Zygomaturus trilobus and Palorchestes azael, both smaller relatives of Diprotodon. Despite often being described as “giant wombats” alongside Diprotodon, these two species are actually somewhat mysterious, with Zygomaturus having been suggested to bear a rhino-like horn, while Palorchestes has been reconstructed with a tapir-like trunk. New fossil discoveries and advances in 3D research techniques are now questioning these earlier hypotheses and are helping us to gain fresh insights into what these giant animals would have been like when they were alive.

Today, kangaroos and wallabies dominate as Lutruwita/Tasmania’s largest marsupials, but in the past, this group was far more diverse. The largest of these was a 150-kilogram giant morph of the forester kangaroo. Despite its size, the shape of its ankle bones indicate that it would still have hopped like a modern kangaroo. Lutruwita/Tasmania was also home to two species of sthenurine, or short-faced kangaroos. These unusual kangaroos are thought to have walked one foot at a time with a striding gait more like a human, rather than hopping like living red and forester kangaroos. Lutruwita/Tasmania also had a giant 130-kilogram ‘wallaby’, Protemnodon anak, with strong arm bones that indicate it may have walked supported by all four limbs.

Perhaps the most unexpected megafauna species in Lutruwita/Tasmania is the long-beaked echidna Megalibgwilia. This extinct species is much larger than the type of short-beaked echidnas we find living in Australia today and is similar to the long-beaked echidnas that live in the mountainous rainforest environments of New Guinea. It is easy to imagine such species struggling to survive alongside glaciers in the cold arid climate of Ice Age Tasmania.

Finally, Lutruwita/Tasmania was also home to Thylacoleo carnifex, a large marsupial predator with bladed cheek teeth and retractable killing claws on their thumbs. This was the undisputed top predator of ancient Tasmania, with characteristic bite marks on the skeletons of other megafauna species indicating that no potential prey was too large for it to handle.

Like the living fauna, the distribution of these extinct Ice Age species was shaped by the changes in sea level that exposed and cut off the Bassian Plain land bridge. But by the end of the last ice age most of these large animals had gone extinct, despite having successfully survived many previous glacial periods. Research continues into the causes of their extinction, with factors such as climate change, human hunting, and landscape modification all likely playing a role. New fossil discoveries will help us to refine our understanding of the timing of these extinctions and may ultimately expand our knowledge of what species were able to successfully travel across the Bassian Plain land bridge to call Lutruwita/Tasmania home.

Jawbone showing the bladed teeth of a marsupial lion Thylacoleo carnifex. This specimen is held within the Tasmanian State Fossil Collection at the Tasmanian Museum and Art Gallery. Photograph by David Hocking. Courtesy of TMAG. CC BY-NC-ND.