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When did kangaroos start to hop?

Scientists have long wondered when the kangaroo’s distinctive leap first appeared. But ancient kangaroo skeletons are so rare that the hop’s origin has remained a mystery. Now, newly discovered 20-million-year-old fossils reveal kangaroo ancestors got their hop on some 10 million years earlier than previously thought.

Before ancient kangaroos started to hop, they got by clinging to tree branches and plucking fruit from the canopies of a lusher, wetter Australia. Hopping is thought to have emerged as this possumlike ancestor transitioned to life on the ground some 10 million years ago, after a dramatic climatic shift dried out the land down under. Researchers reasoned that the simultaneous expansion of grasslands and deserts drove the evolution of the hop—an efficient way to quickly cover the long distances from food source to food source.

But when one of the study authors was sifting through a pile of fossil fragments recovered from northwest Queensland in Australia, he discovered one of the world’s oldest kangaroo fossils. To find out how this ancient kangaroo moved, he and colleagues analyzed the shape and size of fossilized toe and ankle bones. They then used that information to estimate the creature’s range of motion. When the scientists compared it to those of living kangaroos, some of which also climb, they found similarities to modern species adapted for both hopping and climbing.

This extinct animal, not yet named, could move in a variety of ways, including hopping, climbing, and walking, researchers report today in Royal Society Open Science. These results push back the origin of hopping to at least 20 million years ago—and suggest the climatic changes that reshaped the Australian landscape 10 million years later may have simply provided ideal conditions for hoppers to prosper.