Kangaroos Didn’t Always Hop, Evolutionary Biologists Suggest

Quick! Name three things kangaroos always do. Well, that’s easy. They put their young inside pouches, they really like the Australian outback, and they hop around town like nobody’s business.

Shockingly enough, the last one wasn’t always their thing. According to recent research conducted by Brown University scientists, kangaroos didn’t always hop around to get around. In fact, this unique mode of transportation is fairly new — evolutionarily speaking — having appeared in later generations of the marsupial population less than 100,000 years ago.

Christine Janis, an evolutionary biologist and ecologist who led a study reported by phys.org, recently suggested that the present-day kangaroo’s ancestors, the sthenurine kangaroos, didn’t hop away into the Australian sun. Janis and her team suggested that partly due to the sthenurinae’s massive size and bone structure, the Pleistocene animals may have walked bipedally, or by using their feet one step at a time — just like the humans of today.

The study was commenced in 2005, and was inspired by Janis’ visit to a museum, where she was able to view a sthenurine skeleton on display. Janis noticed a striking difference between the ancient kangaroos’ spine and the present-day hopper’s backbones, with the former appearing to be sturdier than the latter.

Sthenurine kangaroo
Sthenurine kangaroo

The biologist then grouped a team of scientists to analyze available data regarding the evolutionary timeline of kangaroos, which involved studying the development of their anatomy. Reviewing the progression of sthenurine evolution, the scientists discovered that the ancient kangaroos stood apart compared to their present-day descendants. Additionally, the sthenurine kangaroos had a teeth structure that suggested they browsed for food, instead of grazing like modern kangaroos do.

Janis also discovered that the large weight the sthenurine kangaroos had to carry would render them unfit for daily hopping. Most of these primitive kangaroos were bigger than the modern ones, with one specimen estimated to have weighed up to 550 pounds.

Janis says, “I don’t think they could have gotten that large unless they were walking.”

Sthenurine kangaroos appear to be more “big-boned” than the modern kangaroos, suggesting that hopping may have been out of the question in terms of transportation. Adding support to her hypothesis, Janis said that older research discovered the sthenurine’s hands weren’t suited to support walking on all fours, leaving bipedal transformation as the most probable mode for the primitive marsupials.

“If it is not possible in terms of biomechanics to hop at very slow speeds, particularly if you are a big animal, and you cannot easily do pentapedal locomotion, then what do you have left?”

The study has been published on the open-access scientific journal PLos ONE.

[Image from Leo/Flickr]

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