Canis lupus hominis

Female mainland thylacines that were living during the Holocene (skull at far left) were much smaller than dingoes from the same time period (skull at far right). This size difference means that dingoes could be effective predators of female thylacines on the mainland and could have been a cause of their extinction.

Thylacines went extinct on the mainland of Australia before European colonization.

They were around on Tasmania up until the twentieth century.

After the Thylacoleo (“marsupial lion”) species became extinct some 40,000 to 50,000 years ago, the thylacines were the largest marsupial carnivores.

And the largest terrestrial predators in Australia. The saltwater crocodiles clearly had them licked, but outside of riparian and coastal areas and in the southern part of the continent, the thylacine was the top “dog.”

However, the reason why the thylacine disappeared from the mainland has been up to conjecture.

Several hypotheses have been propsed.  Almost all involve some discussion of the dingo’s arrival on the continent– a date that is not exactly clear in either the genetic or paleontology literature.

The initial hypothesis was that dingoes simply outcompeted thylacines. Dingoes hunted in packs, and what’s more, as variants of domestic dogs, they would have had a very close relationship with humans.

Pretty much every study about thylacines has made comparisons with those that were in Tasmania during historical times.

These thylacines weighed as much as 70 pounds, and because we have historical accounts a thylacin splitting the skulls of a bull terrier with its jaaws,  it assumes they would have been a match for even a pack of dingoes that included individuals that weighed 30 to 45 pounds. (There is, however, some recent recent research that suggest thylacines had structurally quite weak jaws, so they may not have been all that effective in a combat situation with a mid-sized dog).

However, this is a bit of an unfair comparison.

If one assumes that thylacines that on the mainland when dingoes arrived were exactly like the ones in Tasamania, then it becomes more difficult to see how dingoes could have dominated them. Only by allowing for the dingo’s advantages– such as its association with people, who were on the increase throughout the continent, and the dingo’s pack hunting behavior which allowed it access to wider variety of prey– can we see how a dingo would have dominated the thylacine on the mainland.

However,  a recent study was just published in PLoS One.  In this study, researchers examined the body and skull size thylacine and dingo remains from Nullarbor Plain and the southwestern part of Western Australia that were dated to the early Holocene.

The results revealed something amazing.

Dingoes of that time were quite a bit larger and heavier than mainland thylacine.  The researchers found:

The smallest thylacines were 19.2% and 28.2% smaller than the smallest dingoes in the Nullarbor and southwest, respectively. The largest dingoes were estimated to be 36.8% and 54.1% heavier than the smallest thylacines in the Nullarbor and southwest, respectively.

If thylacines on the mainland were typically that much smaller than dingoes, then they certainly would have been killed by dingoes.

Dingoes are derived from domestic dogs, which are derived from wolves, and we know that wolves kill jackals and coyotes where their ranges overlap.

In fact, canids  in general will kill predators that are smaller than themselves.  Red foxes kill arctic foxes. Coyotes kill red foxes.

Even today, dingoes are effective at controlling fox numbers in Australia.

So it is very possible that larger dingoes were killing thylacines.

The authors of the recent study suggest that the smaller thylacines were female, and unlike Tasmanian thylacines, these mainland individuals had significant sexual dimorphism.

If the dingoes could easily kill these smaller ones, then they were likely killing many female thylacines, and without females, the population could not be sustained.

Of course, the authors point out that all of these relationships were likely much more complex than can be concluded through simple morphological studies.

Dingoes, as feral and semi-domesticated dogs, were attached to people, and the time in which thylacines became extinct is associated with a population increase among indigenous Australians. Indigenous Australians were using fire to manage lands in order to create landscapes that were filled with prey species. They may have even been using the dingoes as hunting dogs, which would make it much easier for them to catch prey.

And if people were doing well, the dingoes likely were, too.  And if the dingoes were doing well, they could have been competing with thylacines for prey.

If their jaw structure meant that thylacines were reduced to preying on smaller animals, dingoes would have had an advantage.  They could hunt larger macropods that were out of the thylacine’s grasp, and they could very easily attack the same prey that thylacines were relying upon.

And if they were also killing thylacines, this would have been very bad for them.

After the extinction of the marsupial lions, the thylacine was the only predatory mammal of any size in Australia.

It evolved without competition.

Dingoes, as derivatives of domestic dogs that evolved from wolves, had derived from lineages that spent millions of years with lots of competition from other predators and very wily, recalcitrant prey.

The wolf had evolved pack-hunting behavior to deal with these challenges.

The thylacine, by all accounts, had not.

One way of interpreting the wolf’s success is that certain wolves evolved to have a relationship with humans. We call the descendants of these wolves domestic dogs. Dingoes are derivatives of domestic dogs, and virtually all accounts suggest that they had some sort of relationship with the indigenous people of Australia.

Thylacines had no relationships with anyone.

The cards were clearly stacked against the mainland thylacine when it went extinct.

Humans were changing the landscape through fire– which allowed human populations to increase.  But that same fire got rid of the forested habitat that thylacines preferred to use to ambush their prey.

And the success of humans also meant that the dingo’s numbers would increase.

And dingoes were much more efficient and generalized predators than thylacines were.

And the dingoes may have considered these mainland thylacines prey.

It was not a good situation for a predator that had spent so many thousands of years evolving without competitors.

And in this case, dingoes were an invasive species.

Over time, they became native, but not after being possibly implicated in the extinction of the mainland thylacine and Tasmanian devil.

It’s not a smoking gun, but dingoes certainly had the opportunity.