Limbless vertebrate

Examples

The jawless fish (hagfish and lamprey) do not have appendage-like fins. They may not have lost them, but rather, simply retained the form that vertebrates had before the evolution of limbs. There are also a number of fish with elongated bodies that have no fins or reduced appendage-like fins, for example eels and swamp eels.

Reptiles have on a number of occasions evolved into limbless forms – snakes, amphisbaenians, and legless lizards (limb loss in lizards has evolved independently over 26 times, examples include the families Pygopodidae and Dibamidae, the subfamily Anguinae and the genus Isopachys). Several species of legless lizards have tiny useless legs, such as pygopodids which retain rudimentary flaps. Contrarily, the worm lizard Bipes as its scientific name suggests has two stubby forelimbs which actually assist in digging similar to a mole. All other amphisbaenians have reduced or absent forelimb girdles.

Larval amphibians, tadpoles, are often limbless. 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).

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, kiwi, 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. Despite its name, the finless porpoise has two fins (the name refers to the lack of a dorsal fin ridge).