Scientists Get Sassy Over The Supposed Extinction Date Of The Tasmanian Tiger

Two of the last thylacines in existence - or are they? EJ Keller/The Smithsonian Institution/Public Domain

Katie Spalding 03 Aug 2018, 16:37

The thylacine – also called the Tasmanian tiger, despite actually being a marsupial that looks uncannily like a dog – is commonly accepted to have made the final leap from endangered to extinct back in 1936, when "Benjamin", the last of the species, died during extreme weather conditions at Tasmania's Hobart Zoo. Despite this, there's a resilient subculture of thylacine-truthers out there who claim the creature is still alive and well – just waiting to be caught on grainy film and prove us wrong.

So they probably weren't very happy last year when a study, led by biologist Colin Carlson and published in the journal Conservation Biology, used mathematical modeling and statistical analysis to calculate the odds that Tasmanian tigers are still running wild and free as being, well, pretty low.

Specifically, they reckoned it was trillions to one.

Now, the, ahem, thylacine awareness community weren't the only people upset by this news. This month, a paper was published – also in Conservation Biology – by a group of biologists who want to dispute this unhappy estimate.

"The last captive thylacine died in the Hobart Zoo in 1936. Beyond this historical fact, the subsequent fate... is shrouded in controversy," the paper begins. "We argue that [the conclusion of Carlson et al.] is unjustifiably confident, given the circumstances of the species’ decline."

It's bad news for marsupial fans though, as the authors make clear that they aren't saying the thylacine is still around.

"Is the thylacine still out there in the wilds of Tasmania? Probably not, but there is enough uncertainty to at least leave this open as a slight possibility," lead author Barry Brook explained to IFLScience.

"[T]he thylacine extinction probably occurred well after [Carlson et al.'s] proposed date of 1940 – perhaps in the 1960s... The exact date is highly uncertain, because of so many confounding ‘known unknowns’."

The main problem, it turns out, is not with the conclusion that the thylacine is probably extinct, but with the probability estimate itself – which they say unfairly disregards important evidence.

"[I]t is irrelevant that all available models suggest that the thylacine is extinct in 2018," Brook said. "It is simply that the statistical sighting models... effectively disregarded ALL non-physical sighting information, irrespective of quality."

So far, so peer-reviewed. But there's a final twist in the thylacine tale.

On the same day, in the same journal that Brook et al.'s paper was published in, Carlson et al. got a rebuttal in – and it's fair to say they aren't convinced.

"Rather than rely on what can barely even be called an ad hoc or back-of-the-envelope calculation, scientifically rigorous work is needed," the authors write about a result used by their challengers. "Brook et al… [seem to ignore] the very reason [these models] were developed," it says elsewhere.

Despite the controversy their claims have caused, Carlson et al. say their main goal is to encourage a refocusing of conservation efforts – arguing that concentrating too much on the elusive thylacine is leading us to forget about other looming extinctions.

"Quantitative tools already exist to help one determine when to stop spending resources on probably extinct species and redirect them toward plausibly salvageable ones… If the thylacine truly exists, it may yet – against all odds – be rediscovered, but other Australian and Tasmanian endemics may still be saved," the paper concludes. "We see no other evidence-based option than to focus on the preventable extinctions that might still be circumvented."

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