We all know that the kangaroos jump: it is their distinctive trait, almost an evolutionary trademark. Jumping, however, is an extremely movement strategy expensive that requires a perfect balance between bones, muscles and tendons. If today the red kangaroo stops comes to weigh on 90 kg, in the distant past Australia was dominated by giant megafauna exceeding 200kg.
Until now, the scientific community was certain of one fact: those ancient giants were too heavy to leave the ground. It was thought that they just walked, a bit like us. Yet, new research published on Scientific Reports reviewed the evidence. By analyzing the fossil remains, scientists discovered that we were there spectacularly wrong: even the most massive prehistoric kangaroos were capable of making spectacular leaps, thanks to an anatomical structure that we had never considered before.
Jump into the past. Today the red kangaroo is the undisputed heavyweight champion among marsupials, capable of leaping in spite of its 90kg. However, for years paleontologists were convinced that there was a “critical threshold”: beyond 150 kg, the laws of physics would have made the jump impossible. If this theory is correct, gigantic prehistoric ancestors such as the Procoptodon — a colossus that grazed the 250 kg — would have been condemned to a slow walk, lacking the agility of their modern descendants.
Steel ankles. A new study byUniversity of Manchester suggests we have underestimated Australia’s megafauna. Instead of simply theoretically “enlarging” a current kangaroo, the researchers analyzed theunique anatomy of extinct species.
The secret of their leap lay in short, stocky foot bones, designed to withstand the violence of impact, and in massive ankles capable of hosting incredibly resistant tendons. These giants not only jumped, but they did so in defiance of all previous calculations, revealing a previously unimaginable structural resistance.
The disadvantages of being big. These anatomical features also had disadvantages: thicker tendons are stronger, but they also retain less elastic energy – in simpler words, the giant extinct kangaroos were jumpers, yes, but not as efficient as today’s ones, and probably only jumped for short (and energetically expensive) periods. It is also possible, according to the fossils, that extinct kangaroos used jumping as part of a broader repertoire of mobility, which also included walking on two or four legs.
