Limbless vertebrate

[2] Reptiles have on a number of occasions evolved into limbless forms – snakes, amphisbaenians, and legless lizards (limb loss in lizards has evolved independently several times, examples include the families Pygopodidae and Dibamidae and species of Anguis, Isopachys, and Ophisaurus).

[3] Contrarily, the worm lizard Bipes as its scientific name suggests has two stubby forelimbs which actually assist in digging similar to a mole.

Adult amphibians have also evolved limblessness multiple times – caecilians, Sirenidae (a clade of salamanders that are limbless except for atrophied front limbs), Amphiumidae (a clade of salamander with extremely atrophied limbs that appear non-functional) and at least three extinct groups (Aïstopoda, Lysorophia, and Adelospondyli).

[8] In the case of limb loss during evolution, vestigial structures testify to this change (remains of the pelvis, rudimentary femur or spurs in boas, pythons and Typhlops).

The evolutionary process of transforming quadrupedal lizards into legless forms results in three main characteristics: the regression of the limbs is carried out gradually, via the reduction in their size and the reduction in the number of phalanges or fingers; the multiplication of the vertebrae (up to 600 in some snakes) induces a lengthening and a gain in flexibility of the trunk; and the vertebral axis is homogenized from the neck to the cloaca, evoking an interminable ribcage.