For nearly a century, scientists have treated the thylacine (Thylacinus cynocephalus) as a textbook case of convergent evolution — a marsupial that independently evolved to look and hunt like a gray wolf (Canis lupus) despite being separated from placental carnivores by 160 million years of evolution. In a new paper published in the journal Nature Communications, researchers from Flinders University, the University of Melbourne and the Australian Museum argue that the thylacine’s skull was not simply a marsupial copy of a canid’s, but a unique combination of traits with no living analogue.
A pair of thylacines, a male and female, c. 1905. Image credit: Smithsonian Institutional Archives / E. J. Keller, National Zoological Park.
Also known as the Tasmanian tiger or the marsupial wolf, the thylacine was a carnivorous marsupial and the apex predator in Tasmania.
The species is one of only a few marsupials to have a pouch in both sexes.
The thylacine looked like an amalgam of several animals. It was the size and shape of a medium-to-large size dog, but had tiger-like stripes running down its lower back and an abdominal pouch.
The fossil record shows that the thylacine appeared about 4 million years ago in Australia. By the 20th century it was extinct, or extremely rare, on the mainland but was still found in Tasmania, the island state off Australia’s southern coast.
The thylacine’s demise can be directly attributed to the bounty scheme in place from 1830-1914 that resulted in the killing of several thousand animals and indirectly to the loss of its habitat from farming activity.
The last known thylacine died in 1936, in Beaumaris Zoo in Hobart, Tasmania, and little is known about the species’ natural behavior.
“The thylacine’s similarity in appearance to gray wolves contributed to an assumed reputation as a livestock predator,” said Flinders University researcher Vera Weisbecker and her colleagues.
“This association prompted, in part, the rapid extermination of the already rare species by British colonizers within 130 years, despite little evidence of meaningful impact on the livestock economy.”
“The thylacine’s extinction marked the end of an over 30-million-year lineage of relatively large-bodied carnivorous marsupials.”
“Unfortunately, this lack of close living relatives means that our understanding of this iconic species’ ecology, and much of its evolution, is limited to anecdotal wild observations and comparisons with living mammals that it may have resembled.”
In the new study, Professor Weisbecker and co-authors conducted detailed 3D shape analyses of thylacine skulls alongside 60 species of carnivorous mammals, including wolves, foxes, big cats and extinct marsupial predators.
They found that while the front of the thylacine’s snout resembled that of small-prey-eating canids like foxes and jackals, the back of its skull looked more like that of its marsupial relatives.
They also found that the thylacine’s skull was strikingly oversized relative to its roughly 17-kg body weight, comparable to the skull size of predators two to four times heavier, such as gray wolves and leopards.
