Data for: Hind limb functional morphology and biomechanical constraints on locomotion in the Triassic cynodont Trucidocynodon riograndensis

Abstract Non-mammaliaform cynodonts occupy a key position in the evolutionary transition from sprawling to more adducted limb postures along the synapsid lineage. Understanding their locomotor capabilities is therefore essential for reconstructing the emergence of mammal-like terrestrial locomotion. Trucidocynodon riograndensis, a probainognathian cynodont from the Late Triassic of southern Brazil, is represented by an unusually complete skeleton preserving an almost intact pelvic girdle and hind limbs, providing an exceptional opportunity for functional analysis. Here we investigate the functional morphology and biomechanical implications of the hind limb of Trucidocynodon riograndensis with the aim of constraining plausible limb postures and movements rather than reconstructing a unique gait. We combine qualitative anatomical analysis, three-dimensional exploration of osteological range of motion and muscle attachment reconstruction with a classical biomechanical model estimating femoral stresses under different postural configurations. The model is used in a comparative and exploratory framework, explicitly acknowledging its simplifying assumptions. The pelvic girdle and hind limb morphology indicate an increased capacity for femoral adduction and fore–aft excursion relative to early sprawling synapsids, while retaining substantial joint mobility. Biomechanical estimates show a consistent trend of decreasing femoral stresses with increasingly adducted limb postures, although calculated stress magnitudes remain well below experimentally determined failure thresholds for limb bones. These results suggest that relatively adducted hind limb configurations were mechanically favourable during weight-bearing, but do not preclude the use of more abducted postures or alternative gait patterns. Overall, Trucidocynodon riograndensis exemplifies an intermediate functional stage in synapsid locomotor evolution, characterised by enhanced parasagittal function without full commitment to the highly constrained limb mechanics of crown mammals. This study highlights the value of integrating functional morphology with classical biomechanical modelling to delimit locomotor plausibility in extinct taxa, while emphasising the inherent uncertainty of gait reconstruction from skeletal remains alone.