Though hopping is the kangaroo’s trademark feature, a prehistoric family of kangaroos may have once walked on two feet, according to a new study by Professor of Biology Christine Janis.
Janis has been looking at bones all her life. Growing up, she was always picking them up and playing with them — an early hobby that developed into a profound love.
“You get an eye for seeing bones,” Janis said.
When she came across the bones of an extinct family of large kangaroos, she was puzzled, she said.
After gathering more data and examining the bone structure further, Janis and her colleagues came to the surprising conclusion: This extinct family of big kangaroos, named sthenurine, walked on two feet. Whereas today’s kangaroos use a pentapedal gait, with the tail acting as a fifth limb, these large creatures moved in a bipedal fashion, Janis said.
“We realized that there is no living analog for this creature, and it falls into its own group,” she said, adding that most other kangaroos hopped even in prehistoric times and no descendants of this type of kangaroo exist.
Sthenurines, sometimes called “giant kangaroos,” were roughly twice the size of a normal kangaroo and are thought to have existed in the Pleistocene epoch, according to the study.
The scientists inspected bones and fossils and analyzed the biomechanical makeup of the family in order to determine its style of gait, according to the article, which was published Oct. 15 in the journal PLOS ONE.
The researchers collected fossils from a variety of museums and institutes, including several locations in Australia, said Karalyn Buttrill ’06, a coauthor on the paper. Buttrill worked on the project as an undergraduate student and traveled to Australia for a semester to collect data for her thesis, she said.
The researchers used the bone measurements to make a map of the animal’s whole body, which allowed them to postulate about the bones’ functions, Buttrill said.
“In order to go from structure to function, you need to have a good sense of anatomy,” Butrill said.
Two features of the sthenurine makeup clued the biologists into the odd nature of its movement, Janis said. First, analysis of bones revealed that the animals had stiff torsos, which would make it difficult to hop. Second, the animal could bear its weight on one leg at a time, an unusual feature for kangaroos, she added.
Snethurines’ walking may have resulted as an adaptation to their eating behavior, Janis said. Since the big kangaroo often gathered food with its arms, it would have been less efficient to use all four limbs to move around. But though bipedal movement may have provided some benefits, it also forced the animal to move at a much lower speed than the kangaroos that hopped, she added.
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