Giant Kangaroo Ancestors Hopped Despite 250kg Bulk, Study Shows

Scientists have found that giant ancestors of modern kangaroos could hop, even at weights up to 250 kilograms. This comes from a study of fossil hindlimb bones published this week, which shows these animals had strong legs built for leaping. The research focused on extinct species from Australia that lived tens of thousands of years ago.

Background

Kangaroos today hop across the Australian outback, using their powerful back legs to cover ground quickly. Their ancestors were much bigger, some as heavy as a small car. These giants roamed Australia during the Pleistocene epoch, a time when the continent had megafauna like huge wombats and flightless birds. Many of these large animals vanished around 50,000 years ago, near the time humans arrived in Australia.

Researchers long thought these giant kangaroos might not have hopped. Their size seemed too great for the bouncing gait that works so well for smaller kangaroos. Instead, some experts suggested they walked or moved in other ways, like quadrupedal steps. Past studies scaled up modern kangaroo bodies to guess at limits, but that approach missed key differences in bone structure.

Fossils of these giants come from sites across Australia, including caves in Queensland. Places like Mt Etna hold remains of species such as Protemnodon, which lived in rainforests 280,000 to 500,000 years ago. Other finds show kangaroos over two meters tall, with legs adapted to forests or open plains. Climate shifts turned lush areas dry and seasonal, which hit these animals hard.

Key Details

The new study looked at hindlimb bones from several extinct kangaroo species. These bones included femurs, tibias, and ankle parts, all key for hopping. Researchers used biomechanical models to test how much force the legs could take. They compared these to modern kangaroos and found the ancient ones had thicker bone walls and stronger joints.

Bone Strength and Movement

Hopping puts huge stress on legs, especially at landing. A 250kg kangaroo hitting the ground generates forces several times its body weight. The fossils showed leg bones strong enough to handle this. Ankle joints had shapes that locked in place during jumps, much like today's species. This setup let them store and release energy efficiently for long hops.

One species, similar to modern red kangaroos but far larger, had hindlimbs that withstood impacts from speeds up to 20 kilometers per hour. Smaller giants, around 100kg, showed even clearer hopping traits. The team ran computer simulations based on fossil measurements, confirming the legs did not break under leaping loads.

Separate work on fossils from Queensland caves adds more. There, giant kangaroos like Protemnodon stayed in small home areas, much like modern ones. They did not roam far, sticking to rainforest patches. Isotope analysis of teeth acted like an ancient GPS, showing they ate local plants and rarely left their spots.

"Using data from modern kangaroos, we predicted these giant extinct roos would have much larger home ranges. We were astounded to find that they didn’t move far at all, with ranges mirroring smaller modern kangaroo species," said Chris Laurikainen Gaete, a PhD candidate at the University of Wollongong.

These homebodies faced trouble as rainforests shrank. Dry seasons grew longer, and food grew scarce in their fixed territories.

What This Means

This hopping ability changes how we see these extinct giants. They were not slow walkers plodding along but active leapers that could flee predators or cross rough ground. In Australia's varied landscapes, hopping helped them reach water or fresh grass during tough times.

The find ties into bigger questions about megafauna loss. Staying local made these kangaroos vulnerable when habitats changed. Humans hunting them in small ranges could have sped their end. Climate alone might not explain it all; their movement style played a role.

For surviving kangaroos, the lesson holds. Modern species hop the same way, thriving across deserts and forests. Understanding ancient limits helps model how today's animals might handle warming climates or habitat loss.

Researchers plan more work on other fossils. They aim to check diets and paths of tree kangaroos and wallabies from the same caves. These smaller kin still live in northern rainforests, offering clues on who adapted and who did not. The tools—bone scans, isotope tests, and movement math—open doors to past lives.

Giant kangaroos hopped into history much like their descendants do now. Their strong legs carried massive bodies over ancient Australia, until conditions shifted too fast even for them.