Aussie carnivores were weird and wonderful

By Marina Kamenev 3 December 2010
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Traditionally thought of as “second-rate mammals”, marsupial carnivores were remarkably diverse, says a new study.

FROM PREDATORS THAT RESEMBLED wolves and lions, to terrifyingly fierce sabre-tooths and oddball Tasmanian devils, marsupial carnivores have been just as diverse as other carnivores over time.

“Their ranks have included creatures as bizarre as the Argentinean pouched sabre-tooth, which sported monstrous, self-sharpening canine teeth that extended almost back into its braincase, and Australia’s own marsupial lion, which had teeth like bolt-cutters and the muscle power to match,” says Dr Stephen Wroe a palaeontologist at the University of New South Wales (UNSW).

“Traditionally, marsupials have been thought of as a poor man’s mammal. They were considered second-rate to their placental cousins,” says Stephen, a co-author of the new study. But his team’s research has found that these animals have been similarly diverse in terms of skull shape, habits, ecology and hunting practices.

Pouched killers

Marsupial and placental mammals split from a shared ancestor 130 million years ago. The main difference is their method of birth; placentals (such as humans, dogs, cats and cows) have lengthy pregnancies and give birth to relatively developed young, whereas marsupials (such as Tasmanian devils, koalas and kangaroos) are pregnant briefly and have young which develop in the mother’s pouch.

Today, the largest living marsupial predator is the 7-kg Tasmanian devil. “There are only a handful of marsupial carnivores weighing more than a few kilograms left in the world today, and it’s because of this they have been thought to be less competitive than placental mammals,” Stephen told Australian Geographic.

Along with a team of scientists, he used physical features to compare 62 species of both living and extinct marsupial and placental carnivores. “We looked mostly at the shape of the skull, as that’s the best window into the behaviour and habits of the species,” says Stephen. The results revealed that marsupial predators were highly varied.

Most of these large species died out millions of years ago; however Thylacoleo, the ‘marsupial lion’, may have survived until 35,000 years ago, making it a contemporary of Australian aborigines. Wolf-like Tasmanian tigers (thylacines) survived until at least the 1930s.

Diversity issues

The extinction of most marsupial carnivores has been attributed to their lack of flexibility and diversity. “[But] this paper suggests that this is not a satisfactory explanation,” comments Dr Colin McHenry a biologist from the University of Newcastle, NSW.

The study highlights the role of luck in the extinction of these species, he says. “A lot of them lived in South America, Australia and Antarctica; these were much smaller continents than the northern continents. Larger land masses are capable of supporting more species, and may offer greater resilience to extinction.”

Professor Mike Archer a palaeontologist also at UNSW not involved in this study calls the lack of respect for marsupial predators “placental chauvinism,” on the part of Northern Hemisphere academics. “It’s a long standing problem,” he says. “I think they have pouch envy.”  

It was believed that marsupials flourished in Australia because there weren’t many placental mammals to compete with them, but the discovery in 1987 of a 55-million-year-old fossil of a placental mammal was the “nail in the coffin of that theory”, Mike says.
Large placental mammals were originally here too, he says “but they were unable to survive the challenging Australian environment.”

The findings are published this week in the Proceedings of the Royal Society B journal.