Tree squirrel Tree squirrel Tree squirrels are the members of the squirrel family (Sciuridae) commonly just referred to as "squirrels". They include over a hundred arboreal species native to all continents except Antarctica and Oceania. They do not form a single natural, or monophyletic group; they are related to others in the squirrel family, including ground squirrels, flying squirrels, marmots, and chipmunks. The defining characteristic used to determine which species of Sciuridae are tree squirrels is dependent on their habitat rather than their physiology. Tree squirrels live mostly among trees, as opposed to those that live in burrows in the ground or
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