Squirrels are members of the family Sciuridae, a family that includes small or medium-size 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.
Phalangeriformes is a paraphyletic suborder of about 70 species of small to medium-sized arboreal marsupials native to Australia, New Guinea, and Sulawesi. The species are commonly known as possums, gliders, and cuscus. The common name "possum" for various Phalangeriformes species derives from the creatures' resemblance to the opossums of the Americas. However, although opossums are also marsupials, Australasian possums are more closely related to other Australasian marsupials such as kangaroos.
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 California ground squirrel, also known as the Beechey ground squirrel, is a common and easily observed ground squirrel of the western United States and the Baja California Peninsula; it is common in Oregon and California and its range has relatively recently extended into Washington and northwestern Nevada. Formerly placed in Spermophilus, as Spermophilus beecheyi, it was reclassified in Otospermophilus in 2009, as it became clear that Spermophilus as previously defined was not a natural (monophyletic) group. A full species account was published for this species in 2016.
Franklin's ground squirrel is a species of squirrel native to North America, and the only member of the genus Poliocitellus. Due to the destruction of prairie, the populations of Franklin's ground squirrel have dwindled, approaching levels of concern. Its decline in the eastern portion of its range is mostly attributed to habitat fragmentation.
Spermophilus is a genus of ground squirrels in the squirrel family. As traditionally defined the genus was very species-rich, ranging through Europe, Asia and North America, but this arrangement was found to be paraphyletic to the certainly distinct prairie dogs, marmots, and antelope squirrels. As a consequence, all the former Spermophilus species of North America have been moved to other genera, leaving the European and Asian species as true Spermophilus.
The white-tailed antelope squirrel is a diurnal species of ground squirrel, scientifically classified in the order Rodentia and family Sciuridae, found in arid regions of the southwestern United States and the Baja California Peninsula of northwestern Mexico.
The Arctic ground squirrel is a species of ground squirrel native to the Arctic and Subarctic of North America and Asia. People in Alaska, particularly around the Aleutians, refer to them as "parka" squirrels, most likely because their pelt is good for the ruff on parkas and for clothing.
The Columbian ground squirrel is a species of rodent common in certain regions of Canada and the northwestern United States. It is the second largest member of the genus Urocitellus, which is part of the tribe Marmotini, along with marmots, chipmunks, prairie dogs, and other holarctic ground squirrels. They are stout, with short dense fur, which is characteristically tawny across the bridge of the nose. Social encounters sometimes are initiated with kissing behavior and the most common activity above ground is standing at attention. Residing in mountainous terrain and high plains in northern latitudes, they hibernate for 8 to 9 months of the year in burrows, which may be used for many years. They are emaciated when emerging in the spring. The Columbian ground squirrel came to the attention of the scientific community through writings produced by Lewis and Clark, while 21st century molecular genetics has more finely illuminated its ties with other close relatives.
The Perote ground squirrel is a species of rodent in the family Sciuridae. It is endemic to Mexico and is currently at risk of extinction. Perote ground squirrels live within the same area as rock squirrels but they use different microhabitats. In one case it also shares its habitat with the Mexican ground squirrel. Perote ground squirrels have traits similar to those of spotted ground squirrels found in the northern Mexican Plateau; however they are larger, have shorter tails and yellow backs. Its skull is relatively narrow with a large braincase and they have heavy, thick teeth. Perote ground squirrels have two annual cycles, an active phase (March–November) and a hibernation phase (December–February). Some overlap may occur in March and November however.
The spotted ground squirrel is a species of ground squirrel in the rodent family Sciuridae. It is found throughout Mexico and the central and western United States. Characterized by a white spotted back, the spotted ground squirrel is one of the smallest squirrels found in North America. They are mainly herbivorous, but also eat insects. A burrowing mammal, the spotted ground squirrel will make tunnels to store its food, as well as shelter and hibernation quarters.
The speckled ground squirrel or spotted souslik is a species of rodent in the family Sciuridae from Eastern Europe. Spermophilus suslicus consists of three subspecies: S. s. boristhenicus, S. s. guttatus, and S. s. suslicus. It is threatened by habitat loss.
Skrjabinema is a genus of nematodes within the Oxyuridae family. Species of this genus typically parasitise ruminants. For example, the nematode Skrjabinema ovis invades the intestinal tract of the guanaco, Lama guanicoe, subsequent to the ingestion of eggs of this worm.
Skrjabinema ovis is a nematode species of the genus Skrjabinema within the Oxyuridae family. This species typically parasitise ruminants. Skrjabinema ovis is known to invade the intestinal tract of the Guanaco, Lama guanacoe, after ingestion of eggs of this worm.
Notocitellus is a genus of ground squirrels, containing two species from Mexico. These species are the tropical ground squirrel, and the ring-tailed ground squirrel (N. annulatus). Notocitellus was formerly placed in the large ground squirrel genus Spermophilus, as a subgenus or species group. Since DNA sequencing of the cytochrome b gene has shown Spermophilus to be paraphyletic to the marmots, antelope squirrels, and prairie dogs, it is now separated, along with six other genera. The exact relations of this genus are unclear, though a relation to the antelope squirrels is possible.
Pygmy ground squirrels are small ground squirrels in the genus Xerospermophilus, family Sciuridae, containing four species from Mexico and the United States. The members of this genus were formerly placed in the large ground squirrel genus Spermophilus. Since DNA sequencing of the cytochrome b gene showed that Spermophilus was paraphyletic to the prairie dogs and marmots, this group is now separated, along with six other genera. Within the genus, the Mohave ground squirrel and the round-tailed ground squirrel were thought to be close relatives, sometimes a subgenus Xerospermophilus, while the spotted ground squirrel and the Perote ground squirrel were formerly placed in the subgenus Ictidomys.
Ictidomys is a North American genus of rodent in the squirrel family, which contains the thirteen-lined ground squirrel, the Mexican ground squirrel, and the Rio Grande ground squirrel. These species were included in the species-rich ground squirrel genus Spermophilus until molecular data showed that this genus was not a natural, monophyletic grouping.
