During the evolutionary history of the frog

Tree frogs are found high in the canopy where they scramble around on the branches, twigs and leaves, sometimes never coming down to earth. The "true" tree frogs belong to the family Hylidae but members of other frog families have independently adopted an arboreal habit, a case of convergent evolution. These include the glass frogs (Centrolenidae), the bush frogs (Hyperoliidae), some of the narrow-mouthed frogs (Microhylidae) and the shrub frogs (Rhacophoridae).[84] Most tree frogs are under 10 cm (4 in) in length, with long legs and long toes with adhesive pads on the tips. The surface of the toe pads is formed from a closely packed layer of flat-topped, hexagonal epidermal cells separated by grooves into which glands secrete mucus. These toe pads, moistened by the mucus, provide the grip on any wet or dry surface, including glass. The forces involved include boundary friction of the toe pad epidermis on the surface and also surface tension and viscosity.[97] Tree frogs are very acrobatic and can catch insects while hanging by one toe from a twig or clutching onto the blade of a windswept reed.[98] Some members of the subfamily Phyllomedusinae have opposable toes on their feet. The reticulate leaf frog (Phyllomedusa ayeaye) has a single opposed digit on each fore foot and two opposed digits on its hind feet. This allows it to grasp the stems of bushes as it clambers around in its riverside habitat.[99]

Gliding

During the evolutionary history of the frog, several different groups have independently taken to the air.[100] Some frogs in the tropical rainforest are specially adapted for gliding from tree to tree or parachuting to the forest floor. Typical of them is Wallace's flying frog (Rhacophorus nigropalmatus) from Malaysia and Borneo. It has large feet with the fingertips expanded into flat adhesive discs and the digits fully webbed. There are flaps of skin on the lateral margins of the limbs and across the tail region. With the digits splayed, the limbs outstretched and these flaps spread, it can glide considerable distances but is unable to undertake powered flight.[101] It can alter its direction of travel and navigate distances of up to 15 metres (49 ft) between trees