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Dingoes led to mainland thylacine's demise


Dingoes were much bigger than mainland thylacines (Source: John Carnemo/iStockphoto)

Dingo dinner The dingo did it according to a new theory on why the iconic thylacine became extinct on mainland Australia about 3000 years ago.

University of New South Wales researcher Dr Mike Letnic, and colleagues, makes the claim in a study published today in PLoS One that shows the dingo was considerably larger than Thylacinus cynocephalus.

He also suggests the introduced predator may have also helped wipe Tasmanian devils (Sarcophilus harrisii) from the mainland.

Thylacines disappeared from the mainland about 3000 years ago - just 500 years after the arrival of dingoes to Australia - but were present in Tasmania until their extinction in 1936.

There has long been debate as to what caused the thylacine to disappear from mainland Australia, Letnic says.

Because the Tasmanian thylacine was much larger than dingoes, direct confrontation between the two species was discarded as a hypothesis for the decline of the Australian marsupial predator.

But Letnic and colleagues at the University of Sydney, have found this wasn't the case with the mainland thylacine, after comparing fossils of it and dingoes found on mainland Australia.

The team took measurements from 21 dingo and 24 thylacine specimens from Holocene deposits in temperate southwest Australia and the semi-arid Nullarbor region of Western Australia.

Completely outmuscled

The smallest thylacines were 19.2 per cent and 28.2 per cent smaller than the smallest dingoes in the Nullarbor and southwest, respectively.

Letnic says the female thylacine was at a particular disadvantage as it was roughly the size of a fox. While male thylacines were about the same size, dingoes were much heavier - in one case by more than 54 per cent.

He says the dingo's size advantage over the thylacine was further exacerbated because dingoes often hunt in packs. Thylacines however were "basically solitary animals or hung out in pairs".

"The thylacine would have confronted groups of dingoes and would have been completely outgunned," says Letnic.

He says the killing of female thylacines by dingoes could conceivably have resulted in extinction if it depressed its reproductive output was less then its rate of mortality.

Letnic says there are modern-day examples of larger predators suppressing the abundance of smaller predators with foxes blamed for the recent loss of the eastern quoll from the mainland.

The larger size of the Tasmanian thylacine, says Letnic, could be explained by a tendency towards gigantism among island populations, or Bergmann's rule which says animals become larger the further they are from the equator.

The researchers also measured the brain sizes of the animals and found the thylacine and Tasmanian devil brains were tiny compared with the dingo. He says this could mean the dingo was able to outwit the other predators.

Human impact?

Letnic says their research does not exclude the possibility that humans were also involved in the extinction of the thylacine on the mainland.

Human population and the development of more sophisticated tools occurred at the same time as the arrival of the dingo on the mainland.

"It is conceivable that both interactions with dingoes and intensification of the human economy may have both contributed to the demise of the thylacine," the paper concludes.

Despite its impact on ancient Australia's ecology, Letnic says recent studies suggest dingoes now play an integral role in maintaining healthy balanced ecosystems.

This is because they fulfill the role the thylacine once held, limiting the populations of herbivores and smaller predators.

Tags: ecology, palaeontology