the loss of limbs in "eupodophis" may have been the result of changes in hox genes, genes that specify the development specific regions of the body. because hox genes are involved in determining specific features of the axial skeleton, the loss of limbs would also result in the loss of cervical (tail) vertebrae that are near them. this loss is seen in "eupodophis" and modern snakes but not legless lizards, which may be far less common because some other factor besides hox genes were involved in the loss of their limbs. the loss of digits on the hind limbs may be explained by a low number of cells in the limb bud during embryonic development.