New research by paleontologists from the University of Bristol, the University of Manchester and the University of Melbourne finds that giant ancestors of modern-day kangaroos had robust hindlimb bones and tendon support capable of withstanding hopping stresses, indicating that size didn’t strictly limit this iconic gait as once believed.
Simosthenurus occidentalis. Image credit: Nellie Pease / ARC CoE CABAH / CC BY-SA 4.0 Deed.
Today, the red kangaroo is the largest living hopping animal and weighs around 90 kg.
But during the Ice Age, some kangaroos grew more than twice the size of that – some reaching up to 250 kg.
For years, researchers believed these giants must have abandoned hopping, as earlier studies suggested that hopping would become mechanically impossible above about 150 kg.
“Previous estimates were based on simply scaling up modern kangaroos, which may mean we miss crucial anatomical differences,” said Dr. Megan Jones, a postgraduate researcher at the University of Manchester and the University of Melbourne.
“Our findings show that these animals weren’t just larger versions of today’s kangaroos, they were built differently, in ways that helped them manage their enormous size.”
In the new study, Dr. Jones and her colleagues studied the hindlimbs of 94 modern and 40 fossil specimens from 63 kangaroo and wallaby species, including members of the extinct giant kangaroo group Protemnodon, which lived during the Pleistocene epoch, between 2.6 million and 11,700 years ago.
For each species they used published estimates of their weight and the length and diameter of their fourth metatarsals — an elongated foot bone key for hopping in modern kangaroos — to calculate whether they could have withstood the strain of hopping.
The scientists then compared the heel bone structures of giant kangaroos with those of modern kangaroo species.
They estimated the size of the tendon required to withstand the forces required to facilitate hopping in giant kangaroos and calculated whether their heel bones would have been large enough to accommodate tendons of this size.
The authors predict that the metatarsals of all giant kangaroo species would have been robust enough to withstand the physical stress caused by hopping, and that their heel bones would have been big enough to allow for the tendon width required for hopping.
Together, the findings suggest that the hindlimbs of all giant kangaroos were robust enough for them to be able to hop.
However, the researchers propose that it is unlikely giant kangaroos would have relied on hopping for all locomotion owing to their large body sizes making this inefficient over longer distances.
They note that sporadic hopping is already seen in many of today’s smaller species, such as hopping rodents and smaller marsupials.
They speculate that short, quick bursts of hopping may have helped some giant kangaroo species evade predators, such as those belonging to a group of extinct marsupial lions known as Thylacoleo.
“Thicker tendons are safer, but they store less elastic energy,” said Dr. Katrina Jones, a researcher at the University of Bristol.
“This likely made giant kangaroos slower and less efficient hoppers, better suited to short bursts of movement rather than long-distance travel.”
“But hopping does not have to be extremely energy efficient to be useful, these animals probably used their hopping ability to cross rough ground quickly or to escape danger.”
“Our findings contribute to the notion that kangaroos had a broader ecological diversity in prehistoric Australia than we find today, with some large species grazers like modern kangaroos while others were browsers — an ecological niche not seen in today’s large kangaroos,” said Dr. Robert Nudds, a researcher at the University of Manchester.
The results appear in the journal Scientific Reports.
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M.E. Jones et al. 2026. Biomechanical limits of hopping in the hindlimbs of giant extinct kangaroos. Sci Rep 16, 1309; doi: 10.1038/s41598-025-29939-7
