A new analysis of fossil bones suggests that Australia's extinct giant kangaroos, once thought too bulky to hop, may have bounced after all. Researchers found adaptations in their leg structures that could withstand the stresses of hopping. These findings challenge long-held assumptions about the locomotion of these massive marsupials.
Australia's Pleistocene-era giant kangaroos, known as sthenurines, weighed more than twice as much as modern red kangaroos, with the largest species, Procoptodon goliah, reaching about 250 kilograms and standing 2 meters tall. These animals went extinct around 40,000 years ago. For years, scientists believed their bulk prevented hopping, forcing them to walk bipedally like humans. However, a study led by Megan Jones at the University of Manchester in the UK has uncovered evidence to the contrary. By examining leg bones from 67 macropod species—encompassing modern kangaroos, wallabies, and extinct giants—Jones and her team measured the femur, tibia, and calcaneus, the bone where the Achilles tendon attaches. They estimated tendon sizes and the forces these structures could handle. In modern kangaroos, the Achilles tendon operates near its breaking point to store elastic energy for efficient hops, a trait that would falter if simply scaled up to giant proportions. Yet, the ancient kangaroos evolved distinct features, such as shorter feet and a wider calcaneus, which helped their bones resist bending during hopping and support larger tendons capable of managing the required loads. 'It’s evidence that they weren’t mechanically barred from hopping,' Jones explains. 'Whether they did hop is a different question.' She suggests hopping might have served for brief speed bursts rather than primary travel. This research aligns with a growing view of kangaroo locomotion as highly adaptable. Benjamin Kear at Uppsala University in Sweden notes that such flexibility in gaits has driven the evolutionary success of macropods over millions of years. Today, red kangaroos can walk using their tail as a fifth limb, while tree kangaroos employ a range of movements, from bounding to quadrupedal walking. The study, published on Research Square, highlights how these extinct giants fit into this versatile family.