Dewlap

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A Mastiff with a dewlap.

A zebu with a fairly massive dewlap, in addition to a protruding hump on its facedown side.

An anole lizard sporting its dewlap.

A dewlap is a flap of skin that hangs beneath the lower jaw of tetrapods, that is, amphibians, reptiles, birds, mammals and their relatives. While the term is usually used in this specific acception, it can also be used to include other structures occurring in the same body area with a similar aspect, such as those caused by a double chin or the sub-mandibular vocal sac of a frog. In a more general manner, the term refers to any pendulous mass of skin, such as a fold of loose skin on an elderly person's neck, or the wattle of a bird. There are also dewlaps on dogs such as the English Springer Spaniel, the Basset Hound or the Mastiff. The dewlap is also found on female rabbits, such as the New Zealand white rabbit. While pregnant, the female rabbit will pluck fur from the dewlap to line a nest for her babies. Although these masses can be referred to as dewlaps, they are formed by stored fat. The Dewlap is also seen in both genders of moose, which may or may not be an indicator of status.

Reptiles, most notably the anole species of lizard, have large skin dewlaps under their neck which they can extend and retract. The dewlaps are usually of a different color from the rest of their body and can be enlarged to make the lizard seem much bigger than it really is, especially when warding off predators. Males use the dewlap to intimidate rivals and to attract females during mating season. Despite the male lizard dewlap being much larger in size, female anoles do indeed possess a dewlap as well. These uses for the dewlap work much in the same way as the neck frill on a frill-necked lizard, with the lizard extending its neck frill for much of the same reasons. However, it is not known if the dewlap is used in thermoregulation like the neck frill is.

Lizards who have dewlaps usually accompany their dewlap enlargement with head bobs and movement. Scientists are unsure about what this is meant to communicate, but it is prevalent when the lizards are courting.