The calcaneus: Insights and speculations from hominin fossils

From
https://www.palaeosa.org/uploads/4/5/2/1/45213539/pssa_abstract_book_final.pdf
Abstract Book
The 22nd Biennial Meeting of the Palaeontological Society
of southern Africa
8 - 13 September 2024, Graaff-Reinet, Eastern Cape
Unraveling the enigmatic calcaneus: Insights
and speculations from hominin fossils
The calcaneus, though often overlooked in
the hominin fossil record due to its
scarcity and fragmentary nature, holds
crucial insights into the locomotor
behaviour and evolutionary history of our
extinct hominin relatives. Despite
incomplete specimens, the diverse
morphological variations observed in
preserved calcanei underscore its
significance as the largest tarsal bone.
This review investigates the calcaneus's
pivotal role in locomotion, highlighting
its articulations with adjacent bones and
its function as a site for muscle
attachment, including the Achilles tendon
and intrinsic foot muscles. Additionally,
unique features such as the medial head of
M. quadratus plantae and the plantar
ligaments distinguish the human foot anatomy.
Comparative analyses with modern apes shed
light on the ancestral calcaneal morphology,
suggesting commonalities in narrow posterior
tuberosity, dorsally positioned lateral
plantar process, and a large peroneal
trochlea. These findings, coupled with
observations from Ardipithecus and
Australopithecus fossils, hint at a more
mobile calcaneocuboid and subtalar joint in
the last common ancestor (LCA) of humans and
apes. The hominin calcaneus presents with
some interesting variations, both
intraspecific and interspecific, in some
instances, without apparent functional
correlates. This adds to the complexity of
understanding the evolution of the human
calcaneus.
Despite these insights, questions remain
regarding the precise morphology of the LCA
calcaneus and its resemblance to modern ape
species. The absence of complete fossils
complicates predictions, leaving room for
further exploration into the evolutionary
trajectories of locomotor adaptations in
hominins.
In conclusion, while the calcaneus may be poorly
represented in the fossil record, its study
offers valuable clues to understanding the
locomotor behaviour and evolutionary history of
our ancestors, illuminating the complex interplay
between morphology, function, and adaptation in
the human lineage.