When studying how fossil hominids moved, researchers usually analyse the morphology of bones - which is crucial for understanding the evolution of bipedalism - focusing mainly on muscle insertion sites. However, the potential information of studying other types of soft tissue, such as joint ligaments, is often overlooked. Now, an article published in the journal Scientific Reports emphasizes the importance of studying the anatomy of the insertion points of the wrist ligaments to reconstruct the locomotor behaviour and manipulative dexterity of fossil hominids throughout human evolution.
The study is led by professors Josep M. Potau and Aroa Casado, from the Human Anatomy and Embryology Unit of the Faculty of Medicine and Health Sciences and the Institute of Archaeology (IAUB) at the University of Barcelona.
With an innovative perspective, the study applies the technique of three-dimensional geometric morphometric analysis (3D GM) to examine the insertion sites of the ligaments at the end of the radius that contacts the wrist (distal epiphysis).
The results confirm the existence of diverse locomotor behaviours in hominids and show significant differences in the size, orientation, and shape of wrist ligament insertions in fossil hominids - Australopithecus afarensis, Australopithecus anamensis, Australopithecus sediba, Paranthropus robustus, Homo neanderthalensis and archaic Homo sapiens - and modern hominids: Homo sapiens, Pan troglodytes (chimpanzees), Gorilla gorilla (gorillas) and Pongo pygmaeus (orangutans).
The study expands the set of methodological tools for understanding the evolution of hominids in palaeoanthropology and proposes an innovative methodology that complements more traditional research based on bone morphology.
A new approach to reconstructing locomotion in hominids
Ligaments are a type of soft tissue that is rarely used in studies of hominid locomotion. They act as stabilizers for the joints and also enable the brain to determine the functional status of each joint. The different forms of locomotion in hominids involve anatomical differences in the ligaments of the wrist and, therefore, modifications in the areas where the ligaments insert into the distal epiphysis of the radius.
"Humans, who are bipedal and use their hands primarily to manipulate objects, have anatomical characteristics in these insertion areas that are markedly different from those observed in other non-human hominoid primates (chimpanzees, gorillas and orangutans)", says Professor Josep Maria Potau, from the Department of Surgery and Surgical Specializations at the UB, "which use their hands differently, mainly due to their arboreal and terrestrial locomotion."
The team developed research lines specializing in the anatomical study of the ligaments of the upper limbs in primates, aiming to create anatomical models that can be compared with modern humans and estimating the types of locomotion of fossil primates by studying the areas of ligament insertion.
