Anatomical insights into fish terrestrial locomotion: a study of barred mudskipper (Periophthalmus argentilineatus) fins based on μCT 3D reconstructions

Mudskippers are a group of extant ray-finned fishes with an amphibious
lifestyle and serve as exemplars for understanding the evolution of
amphibious capabilities in teleosts. A comprehensive anatomical profile of
both the soft and hard tissues within their propulsive fins is essential
for advancing our understanding of terrestrial locomotor adaptations in
fish. Despite the ecological significance of mudskippers, detailed data on
their musculoskeletal anatomy remains limited. In the present research, we
utilized contrast-enhanced high-resolution micro-computed tomography (μCT)
imaging to investigate the barred mudskipper, Periophthalmus
argentilineatus. This technique enabled detailed reconstruction and
quantification of the morphological details of the pectoral, pelvic, and
caudal fins of this terrestrial mudskipper, facilitating comparison with
its aquatic relatives. Our findings reveal that P.
argentilineatus has undergone complex musculoskeletal adaptations for
terrestrial movement, including an increase in muscle complexity and
muscle volume, as well as the development of specialized structures like
aponeuroses for pectoral fin extension. Skeletal modifications are also
evident, with features such as a reinforced shoulder-pelvic joint and
thickened fin rays. These evolutionary modifications suggest
biomechanically advanced fins capable of overcoming the gravitational
challenges of terrestrial habitats, indicating a strong selective
advantage for these features in land-based environments. The
unique musculoskeletal modifications in the fins of mudskippers like P.
argentilineatus, compared to their aquatic counterparts, mark a critical
evolutionary shift toward terrestrial adaptations. This study not only
sheds light on the specific anatomical changes facilitating this
transition but also offers broader insights into the early evolutionary
mechanisms of terrestrial locomotion, potentially mirroring the
transformative journey from aquatic to terrestrial life in the lineage
leading to tetrapods.