https://www.eurekalert.org/news-releases/992054
A Cambridge University researcher has digitally
reconstructed the missing soft tissue of an early
human ancestor – or hominin – for the first time,
revealing a capability to stand as erect as we do
today.
Dr Ashleigh Wiseman has 3D-modelled the leg and
pelvis muscles of the hominin Australopithecus
afarensis using scans of ‘Lucy’: the famous fossil
specimen discovered in Ethiopia in the mid-1970s.
...
Wiseman was able to use recently published open
source data on the Lucy fossil to create a digital
model of the 3.2 million-year-old hominin’s lower
body muscle structure. The study is published in
the journal Royal Society Open Science.
The research recreated 36 muscles in each leg, most
of which were much larger in Lucy and occupied
greater space in the legs compared to modern humans.
For example, major muscles in Lucy’s calves and
thighs were over twice the size of those in modern
humans, as we have a much higher fat to muscle ratio.
Muscles made up 74% of the total mass in Lucy’s thigh,
compared to just 50% in humans.
Paleoanthropologists agree that Lucy was bipedal, but
disagree on how she walked. Some have argued that she
moved in a crouching waddle, similar to chimpanzees –
our common ancestor – when they walk on two legs.
Others believe that her movement was closer to our own
upright bipedalism.
Research in the last 20 years have seen a consensus
begin to emerge for fully erect walking, and Wiseman’s
work adds further weight to this. Lucy’s knee extensor
muscles, and the leverage they would allow, confirm an
ability to straighten the knee joints as much as a
healthy person can today.
...
The Royal Society Open Science paper links for this
don't work but the pre print is open access
https://www.biorxiv.org/content/10.1101/2022.11.24.517817v1.full.pdf
3D volumetric muscle reconstruction of the
Australopithecus afarensis pelvis and limb,
with estimations of limb leverage
Abstract
To understand how an extinct species may have moved,
we first need to reconstruct the missing soft tissues
of the skeleton which rarely preserve, with an
understanding of segmental volume and the muscular
composition within the body. The Australopithecus
afarensis specimen AL 288-1 is one of the most complete
hominin skeletons. Whilst it is generally accepted that
this species walked with an erect limb, the frequency
and efficiency of such movement is still debated. Here,
36 muscles of the pelvis and lower limb were
reconstructed in the specimen AL 288-1 using 3D
polygonal modelling which was guided by imaging scan
data and muscle scarring. Reconstructed muscle masses
and configurations guided biomechanical modelling of the
lower limb in comparison to a modern human. Muscle moment
arms were calculated and summed per muscle group.
Simulated error margins were computed using Monte Carlo
analyses. Results show that the moment arms of both
species were comparable, hinting towards similar limb
functionality. Moving forward, the polygonal muscle
modelling approach has demonstrated promise for
reconstructing the soft tissues of hominins and providing
information on muscle configuration and space filling.
This approach is recommended for future studies aiming
to model musculature in extinct taxa.
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