The Functional and Phylogenetic Implications of the Myology of the Lumbar Region, Tail, and Hind Limbs of the Lesser Grison (Galictis cuja)

Mustelids are a morphofunctionally diversified group. However, there are no descriptions of the postcranial musculature of South American mustelid species except for some comments from the 19th century. Here, we present the first description of the myology of the hind limbs, and lumbar, sacral, and caudal regions of the lesser grison ( Galictis cuja ), a short-legged South American mustelid, including muscle maps and weight data. We interpret the function and the evolution of several muscular features within a comparative framework and through the optimization of these traits onto a phylogeny. The configuration of the axial musculature (e.g., m. quadratus lumborum with short bundles, heavy iliocostalis, and forward originated sacrocaudalis dorsalis) and the presence of strong ankle musculature are features shared with mustelines and, to a lesser degree, with other musteloids. These could be related to a high mobility of the axial skeleton and strong control of the movement of the ankle joint, in relation to the acquisition of epigean bounding gaits, a crouched locomotion, and enhanced maneuverability inside burrows. We recorded many phylogenetically significant traits, shared with other arctoids (e.g., subdivision of m. gluteus profundus and semimembranosus, presence of a single belly for m. sartorius, and absence of articularis coxae) or exclusively musteloids (e.g., frequent fusion between m. piriformis and gluteus medius). Some features (e.g., restricted origin of the caudal belly of the m. semitendinosus, absence of gluteofemoralis, and unusually complex fibularis brevis) seem to be derived conditions acquired in some mustelid clades. Our results sustain the value of myological data for functional and phylogenetic studies.