The ancient kangaroo family sthenurine, which roamed Austraila until about 30,000 years ago, probably wouldn’t have triggered your Kangaroo Jack nostalgia (or if you’re like me, PTSD). It’s true that in some ways they were relatively like modern roos. They did have a long tail and a generally kangaroo-shaped body.
But they also had short, rabbit-like faces. They weighed up to 550 pounds. Some stood more than six-and-a-half feet tall. And they put one leg ahead of the other to walk just like you do, recent research suggests.
Christine Janis, professor of ecology and evolutionary biology at Brown University started investigating how the roos walked when she noticed at a museum that a fossil skeleton of sthenurine, also called a short-faced kangaroo, had a sturdy, stiff spine.
That’d be a big drawback if they were like modern kangaroos, who hop when moving fast and get around on all fours plus some help from their tail when moving slow (pentapedal locomotion). In addition to a flexible spine they’d need a strong tail and hands that could support their weight. Sthenurine struck out on all of those things.
The problem would be even worse as they scaled up. The giant Procoptodon goliah, the nearly seven-foot-tall, up to 550 pound version of the short-faced roo, would have made a very poor hopping machine.
“I don’t think they could have gotten that large unless they were walking,” Janis said.
So Janis and co-authors Karalyn Kuchenbecker, a former Brown undergraduate, and Borja Figuerido, of the University of Malaga, Spain spent years studying and measuring more than 140 modern and ancient kangaroo and wallaby skeletons.
The team found that even if some of the sthenurine hopped for high speeds, at slow speeds walking upright was probably their way of getting around. They found numerous anatomical details to support their findings, such as extra-stable ankles, a broad and flared pelvis that would have supported large gluteal muscles such as those that help humans walk and hands that seem specialized for foraging instead of supporting weight.
“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?” Janis reasoned. “You’ve got to move somehow.”
The question raised is whether the short-faced roo died out because it’s preference for walking over hopping. Janis says that’s not certain, but it is possible being slower made it hard for the big short-faced roos to migrate when they needed to or made it easier for human hunters to chase them down.
[Source: Brown University]
Illustrations of P. Goliath from Brown and Nature