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The genus Draco is a remarkable radiation of about 45 arboreal lizard species, wide spread throughout Southeast Asia. They are known as the flying dragons or flying lizards (although they do not fly, they glide), and are amongst the best of the gliding vertebrates, with several adaptations for generating lift and airfoil in order to move among tall trees in their native forests. Especially important adaptations are elongation of their thoracic ribs to support a gliding membrane, called a patagium, which allows them to glide for long distances, throat lappets to enhance lift and assist in balance, and long streamlined hind limbs with aerodynamic scaling, which also contribute to lift.
Patagium structures are also found in at least two other extant lizard lineages, both geckos, but patagium in Draco species are far larger and supported by active and highly modified musculature. Lizards in this genus show a large size range, spanning a 10-fold difference in body mass between largest and smallest species (between 3-35 grams). However patagium shape is highly conserved among them and scaled allometrically. Recent research finds that larger species of flying dragons are poorer gliders than smaller species, indicating that they do not have behavioral or biomechanical adaptations to compensate for the decreased ratio of lift generation to body size. The four instances of evolution of larger size in Draco lizards occur where multiple species live in overlapping ranges, an observation leading McGuire and Dudley (2005) to hypothesis that the disadvantage of increased size upon gliding ability is only overcome when needed to partition microhabitats among more than one sympatric species.
Draco lizards are highly territorial. Males actively patrol their territories, which include up to several trees, by gliding and never come down to the ground. Females glide through male territories and also do not descend from trees except to lay eggs on the ground. In addition to its use for gliding, the dorsal surface of the patagium is opened and used as a flag in territorial disputes and in courtship, along with a brightly colored dewlap and throat lappets. In general males are more brightly colored than females, although some species have similar coloring of their patagium, and in some species females have stronger coloration. The ventral patagium surface is also sexually dimorphic in coloration; some researchers have proposed that this is so individuals can distinguish flying males and females from below.
A phylogenetic framework of relationships among species was generated in 2001. Ongoing research includes biogeographical studies of the radiation, as well as flight mechanics and evolution, and prediction of gliding performance and capabilities of now extinct Permian and Triassic reptiles that share similar morphological adaptations for flight with the Draco lizards (McGuire and Dudley 2011; McGuire and Heang 2001; McGuire and Dudley 2005).