Prehistoric 'Tasmanian Tiger' was a Tiny Killer

Apr 9, 2014 // by Charles Choi, LiveScience

Nimbacinus dicksoni, a thalycine-like marsupial from the mid-Miocene.

Anne Musser

 

An extinct marsupial hunter only the size of a fox may have hunted prey larger than itself, researchers say.

Kasey-Dee Gardner gets a behind-the-scenes look at how information is extracted from ancient fossils.  Junchang Lü 

 

This predatory ability makes the ancient creature different from its most recent living relative, the also-extinct thylacine, or "Tasmanian tiger." The last known wild thylacine was shot in 1930, and the last captive member of the species died in a zoo in 1936.

Hunting apparently helped drive the species to extinction. People targeted the dog-like Tasmanian tigers because they believed that the animals killed sheep; in fact, a 2011 study published in the Journal of Zoology found that the creatures' jaws were too weak to take down large prey, and that they would have only killed animals smaller than themselves.

The new study analyzed an exceptionally well-preserved whole skeleton of an extinct relative of these last thylacines, known as Nimbacinus dicksoni; the specimen dates to about 11.6 million to 16 million years old. "The discovery of an entire skeleton of Nimbacinus was a truly amazing finding, particularly as it is was in such good condition," said study author Stephen Wroe, a zoologist and paleontologist at the University of New England in Australia.

Tiny lions and carnivorous kangaroos

The marsupial carnivore was about the size of a very large housecat or a small fox, weighing about 11 pounds (5 kilograms). "Its face looked like a cross between a cat and an opossum," said study lead author Marie Attard, a zoologist at the University of New England in Australia.

The modern thylacine (Thylacinus cynocephalus)was larger, comparable in size to a medium-sized or large dog. Modern thylacines weighed in at between 40 and 70 lbs. (20 to 30 kg). Paleontologists discovered the fossil in the mid-1990s in the Riversleigh World Heritage Area in Australia. In ancient times, warm, humid, lowland rainforests covered this region — then, about 10 million to 15 million years ago, it became progressively cooler and drier, transforming into dry open woodlands and grasslands.

Nimbacinus belonged to an extinct family of marsupial carnivores known as the thylacinids, consisting of at least 12 known species. Nimbacinus may have lived in ancient Riversleigh with several other thylacinid species, along with marsupial lions smaller than a housecat and small carnivorous kangaroos, potentially competing with them all for prey. "As a medium-sized carnivore, Nimbacinus was likely hunted by larger meat-eaters, including snakes, ground-dwelling crocodiles and larger species of marsupial lions," Wroe told Live Science.

Aside from studies of the recently extinct thylacine, most knowledge about thylacinids comes from skull fragments, limiting what scientists could deduce about the animals. The newly unearthed Nimbacinus skull, however, helped Attard and her colleagues reconstruct how this creature may have lived.

The skull of an ancient thylacinid from the Riversleigh World Heritage Area in Australia.

Anna Gillespie, University of New South Wales

Modeling a marsupial

The researchers created a 3D computer model of the Nimbacinus skull to realistically simulate how the skull may have behaved. Digitally reconstructing the whole skull posed a challenge, as the top of its cranium had been slightly crushed and only half of its lower jaw, or mandible, was intact. "It was like opening a jigsaw puzzle box, only to find crucial missing pieces," Attard told Live Science.
The scientists then compared the mechanical performance of the Nimbacinus skull with that of the extinct thylacine. They also compared its performance to that of living marsupial carnivores such as the Tasmanian devil, spotted-tailed quoll and northern quoll. These belong to a different and diverse family of marsupial carnivores, the dasyurids.

In a surprise, the researchers discovered the mechanical performance of the Nimbacinus skull was far more similar to the spotted-tailed quoll, a member of a different family of marsupial carnivores, than to the Nimbacinus' closer relative, the thylacine.

These findings suggest Nimbacinus had a powerful bite for its size, was mostly carnivorous and was probably capable of hunting prey larger than itself. "Our biomechanical analysis of the skull of Nimbacinusrevealed that it was likely an opportunistic hunter of the rainforest and had a broadly similar way of life to that of larger living dasyurids such as the spotted-tailed quoll," Attard said. "It likely preyed upon small- to medium-sized birds, frogs, lizards and snakes, as well as a wide range of marsupials, including possums, bandicoots, dasyurids, ancient ancestors of koalas, small wallabies, thingodontans [extinct marsupials with boomerang-shaped molars], marsupial moles and wombats. This suggests possible convergent evolution between Nimbacinus and the spotted-tailed quoll, meaning that these two species independently evolved similar adaptations to similar environments."

In contrast, the recently extinct Tasmanian tiger was considerably more specialized in what it could eat than Nimbacinus and large living dasyurids. This likely made the Tasmanian tiger more restricted in the range of prey it could hunt, "and more vulnerable to extinction," Attard said.

Reconstructing past communities and the ecologies of the species that contribute to them "is pivotal if we are to map out and understand change over time," Wroe told Live Science in an email. "Trying to understand how these animals lived and what they ate is also fun!"

Future analysis of the Nimbacinus skeleton could reveal if it was partially tree dwelling like the spotted-tailed quoll, which could help explain the similarities the researchers have noted so far between the two marsupial species.

The scientists detailed their findings online April 9 in the journal PLOS ONE.

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