Change of vegetation doomed the thylacine

A study from the Australian National University has deepened the findings of an earlier paper that found climate change was the main cause of the extinction of the Tasmanian tiger, or thylacine (Thylacinus cynocephalus).

The study, written by the ANU’s Shimona Kealy and palaeontologist Robin Beck from the University of Salford in the UK, reveals that thylacine populations on mainland Australia went into decline around 14 million years ago, when global temperatures dropped an average of seven degrees Celsius.

The climate change, the researchers say, led to the loss of wet, closed forests and the growth of dry open woodlands – environments to which the tigers were not well adapted.

“We think the structure of tigers’ feet and ankles might have made them better suited to closed forests with uneven surfaces, such as roots and logs, and less well suited to open woodlands,” says Kealy.

At the same time the tree cover was changing and the thylacines were thinning out, another class of marsupials, known as daysurids, began to become more common. The group contains species such as the Tasmanian devil (Sarcophilus harrisii) and the eastern quoll (Dasyurus viverrinus), which share bone structures that make them well adapted to open landscapes.

Whether the daysurids outcompeted the thylacines in the new colder environment is yet to be determined.

“While this study strongly suggests that the cooling, drying climate 14 million years ago was the key change that sparked the diversification of dasyurid species, the exact relationships between dasyurids and thylacines at this time requires further research,” says Ms Kealy.

The study is published in the journal BMC Evolutionary biology.

The findings back up those of a DNA study conducted in 2017 by a team led by Jeremy Austin at the University of Adelaide.

Austin’s team extracted genetic materials from thylacine specimens held in museums and compiled a dataset of mitochondrial DNA for the species.

Analysing the diversity, or lack of it, in the data, the scientists concluded that by the time the thylacine went fully extinct in mainland Australia, around 3000 years ago, it was already on the ropes, it’s population hit hard by with climate changes driven by the El Niño-Southern Oscillation.

The research, published in the Journal of Biogeography, reported that mainland Tasmanian tigers split into eastern and western populations around 25,000 years ago, with the eastern population experience loss of genetic diversity quite quickly.

For reasons not fully understood, a population of thylancines persisted on the island of Tasmania until the twentieth century, when it was rapidly wiped out by European settlers. The last known example of the species died in Hobart Zoo on 1936.

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