Specimen Showcase | Dragons in the Forest🐉

Have you ever dreamed of gliding from one tree to another🌴? If you did, then you may be inspired by the lizard genus 𝘋𝘳𝘢𝘤𝘰 Linnaeus, 1758, also known as the flying lizards which consists of 45 species. Those turned your imagination into reality as they are renowned for their glidings between trees in the rainforests of southeast Asia and southeast India. In contrast to flyers who have to flap their wings to push themselves in the air🦅, gliders only fall from height and move horizontally without any extensive input🪂.

All species of genus 𝘋𝘳𝘢𝘤𝘰 (which can be translated from Latin as Dragon🐉 or large snake) are living at different height within trees where they can use jump from the perches and glide remarkable distances to escape predators, find meals (mainly ants) or to move freely within their territories (i.e., one to several trees). To master this spectacular skill, they have evolved their own “wings” which are composed of elongated movable ribs and specialized muscle groups that support a thin winglike and colourful membrane of skin, known as patagium. When it is not in use, the patagium is folded towards the body like a folded fan. When 𝘋𝘳𝘢𝘤𝘰 sp. jump off a starting point they were perching at a sharp angle, their patagium is then extended by muscle contractions, pulling the ribs forward, followed by a near-horizontal gliding🪂. During landing, their forelimbs are extended forward to enable the hands to grasp the surface, and their heads are moved up and back to prevent them from hitting the landing site. The gliding in this sense covered a horizontal distance of up to 50 meters for some species that are only around 7cm in length😮.

Compared to some fixed-wing aircraft✈️, except for the patagium of 𝘋𝘳𝘢𝘤𝘰 sp. that serve as the primary airfoils, they are also characterized by additional features associated with their gliding. For instance, they have an extensible lappet on the side of their throat and elongated scales on their hindlimb and tails to provide additional lift for flight💨.

But the patagium organ of 𝘋𝘳𝘢𝘤𝘰 sp. is not only used for gliding, but also for reproduction as it is used by males as a display structure. During courtship or territorial conflict between rival males, their patagium is opened, with the extension of their dewlap and throat lappets. Most species exhibit sexual dichromatism in the colouration of the patagium, whereas most of them exhibit “male-biased” dichromatism, meaning males have more brightly coloured patagium♂️.

Surprisingly, it is found that different species of 𝘋𝘳𝘢𝘤𝘰 sp. can occur sympatrically while exhibiting around 10-fold variation in adult body mass ranging between 3 and 35 g😮. Larger species, however, are relatively poor gliders as they have less wing area relative to increased body mass, which without any compensatory mechanisms, reduces their gliding performance. To compensate for this, larger species tend to utilize higher forest strata allowing for higher height lost during gliding🌴. Thus, research indicates that larger species only have a selective advantage when smaller species are also found in the same place.

To observe this wonderful glider, as well as other gliding species such as the flying squirrel among others, and examine their intricate gliding apparatus in person, you may visit the HKBM.

Text: Jacky Sung

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