TASMANIAN tigers had a bounty put on their heads and were hunted to death for allegedly being vicious sheep killers.
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But new research suggests the extinct marsupials were wrongly accused and eradicated.
A Sydney study shows their bite was so weak they could not have tackled large, struggling sheep and would have mainly fed on small animals such as possums, wallabies and bandicoots.
Marie Attard, of the University of NSW, said her team's conclusion came as a surprise, given the reputation of the carnivores.
"Our findings suggest the allegations that they were a major threat to Australia's sheep industry were unjustified."
The discovery, published in the Journal of Zoology, comes just before the 75th anniversary of the death of the last known thylacine, in Hobart Zoo on September 7, 1936.
The researchers used a hospital CAT scanner to create 3D images of the skulls of a thylacine, a Tasmanian devil and a spotted-tailed quoll.
Using the same software that engineers rely on to identify weak points in materials in structures such as aircraft wings, they tested the mechanical strength of the three skulls under different predatory behaviours.
Ms Attard said the thylacine's skull was highly stressed, compared to those of its two close living relatives, during simulations of biting down and tackling struggling prey. Although a thylacine was a large predator, weighing about 30 kilograms, it probably targeted animals weighing as little as five kilograms, pouncing from the bushes to snap them up in its long snout.
"Its rather feeble jaw restricted it to catching smaller, more agile prey," she said.
Ms Attard said historical accounts of thylacine behaviour varied dramatically, with some farmers claiming one animal could kill 100 sheep a year, while others said they hunted in packs.
They may have occasionally attacked very small or weak sheep, but sheep loss was probably due to extreme weather, wild dogs, and theft, she said.
Stephen Wroe, director of the university's Computational Biomechanics Research Group, said the thylacine's reliance on eating small animals could have hastened its demise, because of competition with smaller carnivorous marsupials.
"Just a small disturbance to the ecosystem, such as those resulting from the way European settlers altered the land, may have been enough to tip this delicately poised species over the edge."
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