Arxiu d'etiquetes: geckonids

Herpetological parachuting: gliding amphibians and reptiles

Currently, the only flying reptiles are birds, direct descendants of theropod dinosaurs. Although the age of the great flying reptiles has passed, nowadays, various species of reptiles and amphibians have acquired the ability of gliding to escape their predators. Gliding is defined as falling at an angle less than 45o from the horizontal with the help of membranes that create resistance to the air. In this entry I’ll show you some gliding herp species which currently exist.

Gliding frogs

Gliding frogs (also called “flying frogs”) include species from the Polypedates, Rhacophorus (Rhacophoridae family) and Ecnomiohyla (Hylidae family) genera. These have gained similar characteristics through a process of convergent evolution.

Ecnomiohyla_rabborumPhoto of Ecnomiohyla rabborum by Brian Gratwicke.

Both hylids and rhacophorids are popularly known as tree frogs. Their limbs are specialized for an arboreal lifestyle, with long legs and fingers with sucker-like structures for a better grip.

 Male and female false Malabar's gliding frogs (Rhacophorus pseudomalabaricus) mating. Video by Sandesh Kadur.

The gliding genera have also acquired big membranes on its limbs and between their toes to help them glide and therefore, being able to escape predators more efficiently.

frog_m_1804347aWallace's flying frog (Rhacophorus nigropalmatus) gliding.

Gliding geckoes

Between the members of the Gekkonidae family there are two Southeast Asian genera which have acquired adaptations for gliding: the Ptychozoon genus and the Luperosaurus genus.

P1100785Photo of a Kuhl's flying gecko (Ptychozoon kuhli) by Bernard Dupont.

Geckoes are a group of lizards which have evolved for an arboreal lifestyle which allows them to adhere practically on any surface. Their feet present tiny filaments which allow them to move even upside down.

Ptychozoon_kuhli_mâleDetail of the underside of a Kuhl's flying gecko (Ptychozoon kuhli) in which the skin flaps can be appreciated. Photo by Fenchurch.

The Ptychozoon and Luperosaurus genera also present membranes on their neck, body, limbs and tail that help them to blend in the surface of trees and also to glide at some extent from tree to tree to escape possible predators.

Flying snakes

Speaking of predators, the snakes from the Chrysopelea genus also have developed an efficient method to move through the rainforest’s canopy. The snakes from this genus are diurnal, feed on lizards, frogs, birds and bats, and are found throughout Southeast Asia.

Chrysopelea_paradisi_(6032067972)Couple of Paradise flying snakes (Chrysopelea paradisi) in the Singapore Zoo, by Alan Couch.

Unlike the former gliding herps, flying snakes have no membranes to slow down their descent, instead they have a more complex method. When arriving at the tip of a tree branch, these snakes drop themselves. After a brief fall, they retract their inner organs, compressing them against their thoracic cavity and flaring out their ribs laterally, taking a semi-concave shape, similar to that of a plane’s wing.

biomechanics_1Explicative image of the gliding mechanism of the flying snakes. Image from Biomechanics.

With this method and with the help of serpentine movements, the snakes of the Chrysopelea genus can control with great precision the direction of their descent. These snakes have a more controlled glide than many gliding mammals such as the gliding squirrel and are able to glide through a horizontal length of up to 100 metres.

 Group of scientists testing a Paradise flying snake’s (Chrysopelea paradisi) ability to glide. Video by All of These Videos.

Flying dragons

And we finally get to the most spectacular of all flying herps, the reptiles known as flying dragons. These agamids (Agamidae family) of the Draco genus are found in the tropical forests of Asia, where they survive hunting insects on the forest canopy.

Sans nom-399Photo of a five-lined flying dragon (Draco quinquefasciatus) from Sarawak, Malaysia. Image by Bernard Dupont.

The main characteristic of flying dragons is their ribs, some of which are extremely elongated and present dermal membranes between them acquiring the function of wings. These “wings” are usually retracted against the body and can be erected for both gliding and sending visual signals to other members of their species (wings are usually brightly coloured).

Flying_Dragon_MivartDrawing from the book On The Genesis of Species of the skeleton of a Draco volans.

Flying dragons use their wings to move from tree to tree, to hunt, to escape predators, to chase their own kind during both territorial disputes and courtship. Aside from their brightly coloured wings, many species also present colourful dewlaps (especially males) to indicate their reproductive state to other members of their species.

Draco_spilonotusPhoto of a Sulawesi's lined flying dragon (Draco spilonotus) by A. S. Kono.

The flight record of these agamids is of 60 metres of distance with a vertical descent of only 10 metres. Flying dragons are small, fast and active animals, so few predators are able to hunt them. In addition, they are totally arboreal with only females descending to the ground to lay their eggs underground.

 Flying snake chasing a flying dragon. Video found in Venomous Animals.

As we have seen, most species of gliding amphibians and reptiles live in tropical climates. This is due to the fact that these are habitats with a dense vegetation cover and trees grow very close to one another, allowing these animals to glide from one tree to the other easily. The main threats to these creatures are deforestation and habitat loss since, without an optimal vegetation cover, these animals may be preyed easily by terrestrial predators.

