Anuran Locomotion: Ontogeny and Morphological Variation of a Distinctive Set of Muscles

Adult morphological variation of muscles originating on the iliac shaft (M. iliacus externus, M. internus, and tensor fasciae latae) and vertebrae (M. longissimus dorsi, M. coccygeosacralis, and M. coccygeoiliacus) that are involved in postmetamorphic anuran locomotion was recorded in 41 neobatrachians and coded in 13 more based on the literature, for a total of 54 anuran species. In addition, we explored the spatial and temporal sequences in the ontogeny of these set of muscles from larval series of 19 neobatrachians whose adults differ in locomotion and lifestyle. Our findings suggest that: (1) jumping, swimming, and/or walking are capabilities that could have been achieved from novelties of limbs and protractor muscles of the femur rather than from changes in the axial musculoskeletal system; (2) the initial ontogenetic phase of the locomotion comprises the capability to escape, when the tail is still present; (3) the secondary phase of locomotion comprises changes in the axial skeleton and muscles integrated to the pelvis and might develop simultaneously with the new feeding mechanism of the recently metamorphosed frog.