Dewlap

anole

turkey

A dewlap [doo-lap] is a longitudinal flap of skin that hangs beneath the lower jaw or neck of many vertebrates. While the term is usually used in this specific context, 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 submandibular 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, a drooping protuberance hanging from various parts of the head or neck.

Many reptiles have dewlaps, most notably the anole species of lizard, which have large skin dewlaps which they can extend and retract. These dewlaps are usually of a different color from the rest of their body and when enlarged make the lizard seem much larger. They display them when indicating territorial boundaries and to attract females. Lizards usually accompany their dewlap movement with head bobs and other displays. Though much uncertainty resides around the purpose of these displays, the color of the dewlap and the head bobs are thought to be a means of contrasting background noise.

Many mammals such as dogs, rabbits and moose (elk) possess dewlaps. In zebu cattle, the dewlap is colloquially known as the ‘briefcase folds.’ 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.

Wattles are generally paired structures but may occur as a single structure, in which case it is generally referred to as a dewlap when below the jaw. Both are defined as a ‘caruncle,’ ‘a small, fleshy excrescence that is a normal part of an animal’s anatomy.’ Other caruncles include ‘snoods’ (the protuberances hanging from the forehead of turkeys) and earlobes. In birds, these anatomical features are often an ornament for courting potential mates. Large wattles are correlated with high testosterone levels, good nutrition and the ability to evade predators, which in turn indicates a potentially successful mate. It has also been proposed that ornamental organs such as wattles are associated with genes coding for disease resistance.

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