550-pound Ice Age kangaroos could still hop

Kangaroos have likely been roaming the planet for much longer than experts previously thought. Additionally, the ancestors of today’s marsupials made their jumps while growing. a lot larger than their descendants.

For thousands of years, the largest hopping animal on the planet remained the Australian red kangaroo (Osphranter rufus). A male “Big Red” easily grows to more than five feet tall, weighs 200 pounds and travels about 37 mph at a speed of up to six feet per jump. But as big as they are today, their evolutionary parents were even bigger. During the Ice Age, around 45,000 years ago, the giant kangaroos of the Sthenurines the subfamily often grew to more than double the size of current marsupials. Paleontologists estimate the largest, Procoptodon goliahwas 6.5 feet tall and weighed more than 550 pounds.

It’s easy to assume P. goliah and other giant kangaroos have lost their ability to jump because of all the crowding. After all, scaling a Big Red’s anatomy suggests that the physical act becomes mechanically impossible above 330 pounds. But according to Megan Jones, an evolutionary scientist at the University of Manchester, that’s the problem.

“Previous estimates were based on simple scaling of modern kangaroos, which could mean we are overlooking crucial anatomical differences,” Jones said in a statement. “Our results show that these animals were not just larger versions of today’s kangaroos, but they were built differently, in ways that helped them manage their enormous size.”

In a study published today in the journal Scientific reportsJones and his colleagues argue for a new look at the Ice Age giants. Their conclusions come from comparing the current skeletal anatomy of kangaroos with the fossils of their marsupial cousins. The team specifically focused on two main limitations of jumping: the strength of the bones in the foot and how an ankle could support tendons strong enough to facilitate locomotion.

Unlike today’s kangaroos, the Sthenurines megafauna had thicker, shorter foot bones and wider heels. This combination likely allowed them to handle the intense downward force of the jump using powerful tendons. At the same time, giant kangaroos certainly weren’t constantly hopping across ancient Australian landscapes.

“Thicker tendons are safer, but they store less elastic energy,” said Katrina Jones, a biologist at the University of Bristol and co-author of the study. “This likely made giant kangaroos slower and less efficient, better suited to short movements rather than long-distance travel.”

Jones added that their intermittent jumps weren’t just impressive displays of skill. Giant kangaroos could use them to more easily cross difficult terrain or to escape imminent danger from predators.

It wasn’t about jumping or walking either. Analysis of others Sthenurines fossils suggest a variety of movement options for different species of giant kangaroos. The study authors hypothesize that some may have jumped short distances and then walked on two or four legs as part of a larger “movement repertoire.”

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