Why does a frog need a sacral spine?

The frog has only one sacral vertebra. The pelvic bones are attached to it, and to them, respectively, the hind limbs. Since the frog, like most other amphibians, moves by jumping, it needs strong support of the hind limbs and their connection to the spine. This connection is carried out through the pelvic girdle and the sacral vertebra. This connection of the hind limbs with the spine is characteristic not only of amphibians, but, in principle, for all terrestrial vertebrates.