Anatomy of the hindlimb musculature in the cursorial caviomorph Dasyprocta azarae Lichtenstein, 1823 (Rodentia, Dasyproctidae) : Functional and evolutionary significance

The musculature of the hindlimb of the cursorial caviomorph Dasyprocta azarae is described and functionally evaluated, together with osteological associated traits. Our results show that several features are indicative of emphasized parasagittal movements and stabilized joints. Mm. glutei are relatively well developed, in agreement with an enhanced extension of the hip joint. The relative elongation of the ischium indicates an improved mechanical advantage of the hamstring muscles, required for powerful extension of the hip. M. iliopsoas would act mainly as a protractor of the femur rather than as a rotator. M. peroneus brevis, an evertor and plantarflexor of the foot, is absent. The inversion of the pes would be reduced, such as expressed by the marked reduction of the m. tibialis caudalis. Osteological characters are arranged to facilitate parasagittal movements and to restrict joint mobility. Some features of Dasyprocta (e. g., presence of a gluteal tongue of m. gluteus medius, reduction in number of m. lumbricales, presence of a gluteal crest of the ilium) are interpreted as potential synapomorphies of cavioids. Other features associated to cursoriality (absence of mm. peroneus brevis, reduction of m. tibialis caudalis) would have been acquired independently in the extreme cursorial cavioids Dasyprocta and Dolichotis.