【進化学】二足歩行を始める前の類人猿

The fossil of a previously unknown species of ape found in Germany is reported in a paper published this week in Nature. This specimen, which lived during the Miocene about 11.6 million years ago, sheds light on what apes may have been like before they were bipedal.

Many ideas have been proposed to explain the origin of hominin bipedalism and great ape suspension, but fossil evidence has been lacking. It has been suggested that hominin bipedalism evolved from a quadruped that puts its entire foot on the ground, similar to living monkeys, or from a more suspensory quadruped, most similar to extant chimpanzees.

Madelaine Bohme and colleagues describe a new fossil ape, named Danuvius guggenmosi, with complete limb bones. The authors suggest that this specimen provides evidence of a newly identified form of positional behaviour that they call ‘extended limb clambering’. This ape would have been able to hang from branches by its arms. However, unlike other apes such as gibbons or orangutans, which do not use their legs as much as their arms for locomotion, this species had hindlimbs that were held straight and could have been used to walk on. This ape also had a grasping big toe, which meant it would have walked on the sole of its feet.

The authors conclude that D. guggenmosi illustrates a way in which apes began to walk on their hind legs before they reached the ground.