Arboreal locomotion small branches, as they may wrap too far around and prick the animal's own paw. Adhesion is an alternative to claws, which works best on smooth surfaces. Wet adhesion is common in tree frogs and arboreal salamanders, and functions either by suction or by capillary adhesion. Dry adhesion is best typified by the specialized toes of geckos, which use van der Waals forces to adhere to many substrates, even glass. Frictional gripping is used by primates, relying upon hairless fingertips. Squeezing the branch between the fingertips generates a frictional force that holds the animal's hand to the branch. However, this
Lost Animals of the 20th Century such is unavailable, the live materials feature existing species that share the closest characteristics with the extinct animal. Although the show specifically deals with animals that have become extinct, there was one episode that featured the theme of animals which were thought to be extinct, but have been rediscovered. Such has also been the case of some previously featured animals in the show, as scientists have eventually rediscovered extant populations or are attempting to revive species through selective breeding/cloning. Among the animals featured are: Lost Animals of the 20th Century Lost Animals of the 20th Century is a 16-episode documentary