3D model of the reconstructed muscle structures of the locomotor system of the Australopithecus afarensis woman “Lucy”. © Dr Ashleigh Wiseman
On the trail of musculature that is 3.2 million years old: The functional reconstruction of the soft tissue of the famous pre-human woman “Lucy” confirms that the musculoskeletal system of Australopithecus afarensis probably already worked in a similar way to ours: the pre-humans stood on straight legs and also strained when walking the knee all the way through. The results now show further potential for research into movement systems in the representatives of the human family tree.
She’s a “world star” of anthropology: since its discovery in 1974, the fossil of the pre-human female, nicknamed “Lucy,” has garnered a lot of attention. Because this creature, which roamed East Africa 3.2 million years ago, possessed an intriguing mix of simian and human features. Since then, more fossils of the hominin species, dubbed Australopithecus afarensis, have been discovered. However, at 40 percent of the skeleton, Lucy still represents the fossil with the most extensive bone inventory of her species.
It turns out that Australopithecus afarensis still had a rather ape-like face and a relatively small brain. While there are still signs of anatomical adaptations to climbing trees, studies of the musculoskeletal system make it quite clear that these pre-humans walked on two legs. Findings of petrified footprints from the find region also support this. To what extent their mode of locomotion actually resembled ours is unclear. Some anthropologists suspect an already quite advanced gait. Others think that Australopithecus afarensis still moved in a crouched, waddling gait with slightly bent knees – similar to chimpanzees, which briefly walk on two legs.
Still clumsy or already advanced?
To get more clues, Ashleigh Wiseman from the University of Cambridge has now digitally reconstructed the musculature of Lucy’s musculoskeletal system. “Muscle reconstructions have already been used to determine the running speed of a T. rex, for example,” says the biomechanics expert. “Also, Lucy’s ability to walk upright may be reflected in the reconstruction of her muscles,” Wiseman says. In order to digitally reproduce the soft tissue that was not preserved, the scientist began examining modern humans. Using data from MRI and CT scans of the muscle and bone structures, she recorded the relevant structures. She mapped the muscle tracts and developed a digital model that could serve as the basis for studying the musculoskeletal system of Australopithecus afarensis.
Wiseman then used existing virtual models of Lucy’s skeleton to reconstruct her muscles. The data also includes information about certain traces on the bones that indicate former soft tissue structures. The researcher finally developed a model of the approximately 3.2 million year old musculoskeletal system, which includes a total of 36 individual muscles of the hip and leg area. The results also allowed conclusions to be drawn about leverage effects and joint functions: axes could be defined around which the limbs could move and rotate, the scientist explains.
A stretched knee is evident
As she reports, her results support the assumptions of an already quite advanced locomotion system in Australopithecus afarensis: “Lucy’s muscles indicate that she was already as good at bipedalism as we are, although she was possibly still at home in the trees. However, it probably walked in a way that we can no longer see in any other species alive today,” says Wiseman. At least pre-humans could apparently already stretch their knee joints as far as modern humans, according to the characteristics of the reconstructed “knee extensors” and the derived leverage effects. “Australopithecus afarensis roamed both open wooded grasslands and denser forests in East Africa three to four million years ago. The reconstructions of Lucy’s muscles suggest that she would have been able to use both habitats effectively.”
As Wiseman concludes, their results now also illustrate the fundamental potential for using digital muscle reconstruction for anthropology: “By applying this technique to different members of our family tree, we could uncover the range of physical movement that drove our evolution – including the skills we’ve lost,” said the scientist.
Source: University of CambridgeArticle: Royal Society Open Science, doi:10.1098/rsos.230356