Squirrels are members of the family Sciuridae, a family that includes small or medium-sized rodents. The squirrel family includes tree squirrels, ground squirrels, and flying squirrels. Squirrels are indigenous to the Americas, Eurasia, and Africa, and were introduced by humans to Australia. The earliest known fossilized squirrels date from the Eocene epoch, and among other living rodent families, the squirrels are most closely related to the mountain beaver and to the dormice.
Flying squirrels are a tribe of 50 species of squirrels in the family Sciuridae. Despite their name, they are not in fact capable of full flight in the same way as birds or bats, but they are able to glide from one tree to another with the aid of a patagium, a furred skin membrane that stretches from wrist to ankle. Their long tails also provide stability as they glide. Anatomically they are very similar to other squirrels with a number of adaptations to suit their lifestyle; their limb bones are longer and their hand bones, foot bones, and distal vertebrae are shorter. Flying squirrels are able to steer and exert control over their glide path with their limbs and tail.
The southern flying squirrel or the assapan is one of three species of flying squirrel found in North America. It is found in deciduous and mixed woods in the eastern half of North America, from southeastern Canada to Florida. Disjunct populations of this species have been recorded in the highlands of Mexico, Guatemala, and Honduras.
The northern flying squirrel is one of three species of the genus Glaucomys, the only flying squirrels found in North America. They are found in coniferous and mixed coniferous forests across much of Canada, from Alaska to Nova Scotia, and south to the mountains of North Carolina and west to Utah in the United States. They are light brown with pale underparts and grow to a length of 25 to 37 cm. They are proficient gliders but uncoordinated walkers on the ground. They feed on a variety of plant material as well as tree sap, fungi, insects, carrion, bird eggs and nestlings. They mostly breed once a year in a cavity lined with lichen or other soft material. Except when they have young, they change nests frequently, and in winter a number of individuals may huddle together in a shared nest. Unlike most members of their family, flying squirrels are strictly nocturnal.
Sciurinae is a subfamily of squirrels, uniting the flying squirrels with certain related tree squirrels. Older sources place the flying squirrels in a separate subfamily (Pteromyinae) and unite all remaining sciurids into the subfamily Sciurinae, but this has been strongly refuted by genetic studies.
The mountain beaver is a North American rodent. It is the only living member of its genus, Aplodontia, and family, Aplodontiidae. It should not be confused with true North American and Eurasian beavers, to which it is not closely related; the mountain beaver is instead more closely related to squirrels, although its less-efficient renal system was thought to indicate greater relative antiquity for the species. There are seven subspecies of mountain beavers, six of which are found in California and three of which are endemic to the state.
The three species of New World flying squirrels, genus Glaucomys, are the only species of flying squirrel found in North America. They are distributed from Alaska to Honduras. They are similar in many ways to the Eurasian flying squirrels in the genus Pteromys. Two species of New World flying squirrels can be easily distinguished on the basis of size and ventral pelage. Northern flying squirrels, Glaucomys sabrinus are larger and have belly hair that is dark at the base and white at the tip. Southern flying squirrels, Glaucomys volans, are smaller and have belly hairs that are completely white. Humboldt's flying squirrel is more difficult to distinguish from the northern flying squirrel where their ranges overlap. In fact, they were once considered conspecific. Humboldt's flying squirrel is considered a cryptic species. They are generally smaller and darker than northern flying squirrels.
Garrido's hutia is a small, critically endangered, rat-like mammal found in coastal mangrove forests on Cuba and nearby islands. It is rarely seen and may be extinct. It is a member of the hutia subfamily (Capromyinae), a group of rodents native to the Caribbean that are mostly endangered or extinct. The only other species in its genus, the Desmarest's hutia, is also found only on Cuba.
A number of animals are capable of aerial locomotion, either by powered flight or by gliding. This trait has appeared by evolution many times, without any single common ancestor. Flight has evolved at least four times in separate animals: insects, pterosaurs, birds, and bats. Gliding has evolved on many more occasions. Usually the development is to aid canopy animals in getting from tree to tree, although there are other possibilities. Gliding, in particular, has evolved among rainforest animals, especially in the rainforests in Asia where the trees are tall and widely spaced. Several species of aquatic animals, and a few amphibians and reptiles have also evolved this gliding flight ability, typically as a means of evading predators.
The Hawaiian hoary bat, also known as ʻōpeʻapeʻa, is a species of bat endemic to the islands of Hawaiʻi. The Hawaiian hoary bat occupies the major Hawaiian islands, making it the only extant and native terrestrial mammal in the islands. Some studies report that the mainland hoary bat lives in sympatry on the Hawaiian Islands alongside the Hawaiian hoary bat, although this is disputed. The Hawaiian hoary bat was officially named the state land mammal of Hawaiʻi in 2015. It is a federally listed endangered taxon of the United States.
The Isla De La Juventud tree hutia or southern hutia is a subspecies of rodent in the subfamily Capromyinae. It is endemic to lowland moist forests on Isla de la Juventud in Cuba. It is threatened by habitat loss and is considered Critically Endangered by the IUCN Red List.
The Indian giant flying squirrel, also called the large brown flying squirrel or the common giant flying squirrel, is a species of rodent in the family Sciuridae. It is capable of gliding flight using a skin membrane, the patagium, stretched between front and hind legs. It is found in mainland Southeast and South Asia, and southern and central China.
The Japanese dwarf flying squirrel is one of two species of Old World flying squirrels in the genus Pteromys. During the day this squirrel hides in a hole, usually in a coniferous tree, emerging at night to feed.
The Prince of Wales flying squirrel is a subspecies of the northern flying squirrel endemic to Prince of Wales Island and a few neighboring islands in the Alexander Archipelago of Alaska.
The Vangunu giant rat, locally known as the vika, is a giant arboreal species of rodent in the family Muridae. The rat was discovered in the island of Vangunu in the Solomon Islands in 2015, after years of searching based on local stories, and described in 2017. It was identified as a new species on the basis of its skull, skeleton and a detailed DNA analysis. The single individual initially collected from a felled tree measured 46 cm (18 in) long, weighed between 0.5 and 1.0 kg and had orange-brown fur. Its diet is believed to include thick-shelled nuts like ngali nuts and coconuts, and probably fruits. The species is likely to be designated critically endangered, due to the small amount of forest habitat remaining on the island and ongoing logging. In 2021, the species was observed in the wild for the first time, with at least four individuals being observed via camera trap in Vangunu's last remaining lowland primary forest. They are highly threatened by proposed logging plans for their remaining habitat.
The Humboldt marten is an endangered, genetically distinct subspecies of the Pacific marten known from the old-growth coastal redwood forests, forests with dense shrub cover, areas with serpentine soils, and forested areas with dense understory cover of the U.S. states in coastal California and Oregon.
The Pacific marten is a species of North American mammal, a member of the family Mustelidae. It is found throughout western North America.
The southwestern red squirrel or Fremont's squirrel is a species of tree squirrel endemic to high-altitude regions of the southwestern United States.
