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
Divergent evolution in animals insects are believed to be a result of needing the ultrasonic hearing that tympanal ears provide in order to hear predators in the dark. Non-nocturnal insects - that do not need to fear nocturnal predators - are often found to lack these tympanal ears. Animals undergo divergent evolution for a number of reasons. Predators or their absence, changes in the environment, and the time at which certain animals are most active are chief among them. A lack of predators – predatory birds and mammals - for cliff-side nest residing kittiwake caused that particular group of kittiwake to lose their ancestral