Limbless vertebrate


Many vertebrates have evolved limbless or limb-reduced forms. Reptiles have on a number of occasions evolved into limbless forms - snakes, amphisbaenia, and legless lizards ''. The same is true of amphibians - caecilians, Sirenidae, Amphiumidae and at least two extinct groups. Legless forms of reptiles and amphibians probably evolved so as to be able to move underground or in water more easily.
There are also a number of fish with elongated bodies that have no or reduced appendage-like fins, for example eels and swamp eels. While hagfish and lamprey also do not have appendage-like fins, they may not have lost them, but simply retained the form that vertebrates had before they evolved limbs.
There are no known limbless species of mammal or bird, although partial limb-loss and reduction has occurred in several groups, including whales and dolphins, sirenians, kiwis, and the extinct moa and elephant birds. The moa in particular are notable for having completely lost their wings, without even vestigial wings remaining outside their bodies. Names can be deceiving, as the finless porpoise has two fins, and several species of legless lizards have tiny useless legs.