The ilio-sacral articulation in frogs: form and function

Abstract

The amphibian order Anura (frogs) is a major group whose origin appears related to the transformation of its locomotor system for saltation. However, the ilio-sacral articulation, a uniquely specialized part of the frog locomotor morphology, remains largely unstudied. Preliminary work reveals significant differences in the morphology of the ilio-sacral articulation among extant frogs and suggests that differences in types of articulation are correlated with different directional movements at the joint, with specific locomotor modes, and wim phylogenetic groupings. SUMMARY The morphology of the ilio-sacral articulation in frogs is correlated with different patterns of mobility at the joint and different locomotor behaviors. Overlain on diese basic differences in articulation among frogs is variation in other aspects of pelvic and vertebral morphology as well: muscle origin and insertion, urostyle fused or free, length and angle of the ilia, length of transverse processes of the pre-sacral vertebrae, and die articulation pattern of die presacral vertebrae. Obviously, the role of these additional morphologies must be established and integrated with the data on articular morphology before die form-function complex is completely understood. This paper is the first step towards that end, and work on other aspects of pelvic and vertebral morphology is underway.