One of the most fascinating periods in the evolution of the human lineage is the appearance of the first ancestors capable of bipedalism. Knowing the type of locomotion used by many fossil species - walking upright on the ground or climbing from branch to branch with the strength of their arms - has been one of the most classic questions in the study of the process of hominization. Now, a paper published in the American Journal of Primatology provides new insights into how and when bipedal locomotion appeared during human evolution.
Professor Josep M. Potau, from the Human Anatomy and Embryology Unit of the Faculty of Medicine and Health Sciences and the Institute of Archaeology of the University of Barcelona (IAUB), leads this study. Neus Ciurana, from the Gimbernat University School, is the first author of the article, which includes the participation of teams of the University of Valladolid.
The study helps to infer how some fossil hominin species moved through an innovative technique that analyses and compares muscle insertion sites characteristic of locomotor behaviour in Hominidae primates (chimpanzees, bonobos, gorillas, orangutans and humans).
The conclusions corroborate that specimens of Australopithecus and Paranthropus combined bipedal locomotion with an arboreal locomotion similar to that of current bonobos (Pan paniscus), the species most phylogenetically related to humans that combines ground and arboreal locomotion, as well as occasional bipedalism episodes. The results of the study also state the presence of arboreal locomotion in Australopithecus sediba - a still little-known species - and in Paranthropus boisei, a fossil hominin that has aroused a certain scientific controversy regarding the way it moved around.
3D technology to study key areas in brachiating primates
The team has used a new methodology that involves making 3D scans of the ulna bone of present-day humans, present-day hominoid primates and fossil hominins. This technique makes it possible to identify and compare with greater precision the insertion sites of the brachialis and triceps brachii muscles in the proximal epiphysis of the ulna, an anatomical area that is decisive in arboreal locomotion (brachiation).
Josep M. Potau, member of the UB's AEPPRI research group(Anatomia Evolutiva i Patològica dels Humans i altres Primats), notes that "the elbow is a joint formed by three bones - humerus, ulna and radius - and its flexion-extension and pronation-supination mechanisms play a key role in different types of arboreal locomotion widely used by primates. This is due to the functional importance of the muscles that act on the joint, especially the brachialis, which participates in elbow flexion, and the triceps brachii, which participates in elbow extension".
