Thylacine was not a wolf, but a tiger

Thursday, 5 May 2011

by Taylor Burns

Cosmos Online

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A pair of thylacines photographed at the Smithsonian’s National Zoo circa 1906.

Credit: Wikimedia

CAMBRIDGE: New evidence that the recently extinct thylacine - Tasmania's 'king of beasts' - may have been less wolf-like than previously thought, according to a new study.
In popular science vernacular, the thylacine has been commonly referred to as either the 'marsupial wolf', due to its superficially dog-like features, or 'Tasmanian tiger', due to its striped fur coat. A quantitative, skeletal analysis by Christine Janis and Borja Figueiredo from Brown University in Rhode Island provides support for the suggestion that thylacines were not pursuit predators, with particular emphasis on the animal's ability to rotate its elbow.
The study, published in Biology Letters, questions the degree to which the thylacine was a 'marsupial wolf', and perhaps suggests 'Tasmanian tiger' to be a more appropriate vernacular label.
""It's become the icon of marsupial and placental convergence, so it's a good thing to point out that it's not the exact analogue of the wolf," said Janis. "Nobody has really done a more modern quantification of any part of the skeleton, that we did here."
Discovering the 'Tasmanian tiger'
The thylacine was the largest marsupial carnivore on Australia's mainland, the last of them thought to have lived up to 3,000 years ago. Shortly after the appearance of dingoes 4,000 years ago, the dwindling population of thylacines lived exclusively in Tasmania.
When discovered, scientists saw the now-extinct animal as a textbook example of convergence between marsupials (such as kangaroos) and placentals (such as wolves). The skull of the thylacine received much attention, with several studies confirming the animal's carnivorous diet and wolf-like skull - its species name, cynocephalus, translates to 'dog head'.
But recently, researchers have been increasingly sceptical of the evolutionary link between thylacines and wolves, suggesting that thylacines specialised on smaller prey instead of large-prey pack hunting, and that their skeleton is not well-adapted to the running abilities of dogs.
Head of a wolf, elbow of a tiger
The new study now adds postcranial evidence that the thylacine was poorly adapted to wolf-like behaviour, confirming rare eyewitness reports of more predatory hunting rather than pack pursuit. Though several morphological characteristics were examined, the most telling was the thylacine's elbow.
To exhaust their prey, pack-hunting wolves have their forepaws 'locked in' for marathon running, whereas other predatory animals have more flexible, manipulative forearms. By comparing the thylacine elbow to more than 30 other animals, Janis and Figueirido discovered that, similar to the latter group, the thylacine's elbow allowed for both pronation and supination of the forearm - a highly flexible, non-wolf-like characteristic.
But this is not to say that the thylacine is cat-like. Its claws are not retractile or effective in grabbing prey. Rather, it simply lacks some of the essential features of dogs that are associated with fast running. The head is wolf-like, but the postcranial skeleton is not.
Dingoes and the 'niche overlap hypothesis'
This finding raises questions about why the thylacine initially disappeared. It has been widely speculated that the thylacine was pushed out of Australia because the dingo had similar predatory techniques and thus competed for the same food - the so-called 'niche overlap hypothesis'.
The duo's research makes clear that there is less convergence between thylacines and large canids - like wolves or dingoes—than was previously assumed, meaning the niche overlap hypothesis might be overstated. However, this still does not explain the coincident timing of the thylacine's disappearance.
"There is a low probability that the arrival of the Dingo and coincident disappearance of the thylacine from mainland [Australia] is a coincidence," said Michael Archer, a palaeontologist at the University of New South Wales who initiated attempts to clone the thylacine. "[This is] aaugmented by the fact that dingoes never got to Tasmania, which is where thylacines survived until we blew them out of existence after 1788."
Are there still some out there?
The problem, said Janis, is that is very difficult to know what prey was hunted by dingoes and thylacines. There is simply a lack of information.
"I'm not saying dingoes had nothing to do with it, they may well do," said Janis. "But I'm saying that they are not the exact same kind of ecological counter animal, so I think we need to look at that a little more carefully."
Until then, Janis - a frequent visitor to Australia with a 'house full of thylacine memorabilia'- will continue to be inspired by the mystery surrounding one of Australia's most mythical creatures.
"I'm still holding out a very vague hope that there are some out there somewhere," said Janis. "I don't think it's likely, but I think it's not impossible. The mystery makes it so appealing."