Skeletons serve as the body’s fundamental structure and perform multiple vital functions, and thus even subtle modifications can lead to functional changes. However, studies on sexual shape dimorphism in the appendicular skeletons of anurans remain scarce, especially for fossorial species. Herein, we investigated the sexual differences in the external morphology and internal skeletal shape of girdles and limbs of fossorial Kaloula rugifera during the breeding season. The results reveal the following: (1) Males exhibit significantly longer forelimbs and hindlimbs, suggesting advantages in male—male competition and amplexus. (2) Males possess more curved and dilated coracoids and broader pubis-ischium regions, which may enhance forelimb contraction efficiency and hindlimb locomotor performance. (3) Males feature a more developed crista ventralis, likely enhancing forelimb flexion for tightly grasping females during mating. In contrast, females display a torsioned femur and robust hindlimb morphology, suggesting adaptations for digging and load-bearing. These findings provide insights into how anurans optimize reproductive fitness and ecological adaptations through morphological specialization. To our knowledge, this study presents the first examination of sexual shape dimorphism in anuran appendicular skeletons utilizing three-dimensional geometric morphometrics.

Sexual dimorphism is prevalent among animals, influencing both functional morphological traits and behavioral performances. In this study, we investigated the sexual differences in the morphological parameters of Kaloula borealis (Anura, Microhylidae) during the breeding season using 48 specimens. Our results reveal that among the 16 external morphological traits, females had significantly larger snout-vent length and eye diameter than males. The former presumably contributes to enhancing fertility, while the latter is associated with larger body size. Males exhibited significantly greater head width and thigh width than females, which may be related to accessing a wider range of food sources and enhancing their locomotor ability, respectively. Among the 32 appendicular muscles, 10 displayed significant sexual dimorphism in dry mass, suggesting divergent reproductive strategies between the sexes. Among the eight internal organs analyzed, males possessed significantly heavier hearts and lungs than females, which is likely an adaptation to higher metabolic demands and calling behavior. Collectively, our findings demonstrate that sex-specific differences in external morphology, muscle mass, and internal organ mass reflect distinct ecological and reproductive adaptations between males and females and contribute to the phenotypic diversities in Anura.