Squirrel in the context of Tree squirrel

Rodents (from Latin rodere, 'to gnaw') are mammals of the order Rodentia (/roʊˈdɛnʃə/ roh-DEN-shə), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are native to all major land masses except for Antarctica, and several oceanic islands, though they have subsequently been introduced to most of these land masses by human activity.

Rodents are extremely diverse in their ecology and lifestyles and can be found in almost every terrestrial habitat, including human-made environments. Species can be arboreal, fossorial (burrowing), saltatorial/ricochetal (leaping on their hind legs), or semiaquatic. However, all rodents share several morphological features, including having only a single upper and lower pair of ever-growing incisors. Well-known rodents include mice, rats, squirrels, prairie dogs, porcupines, beavers, guinea pigs, and hamsters. Once included with rodents, rabbits, hares, and pikas, which also have incisors that grow continuously, are now considered to be in a separate order, the Lagomorpha, distinguished by an extra pair of incisors. Both Rodentia and Lagomorpha are sister groups, sharing a single common ancestor and forming the clade of Glires.

A camel-hair brush is a type of paintbrush with soft bristles made from natural hairs, usually squirrel. Actual camel hair is not a suitable material, although historically camel was used for ancient Chinese ink brushes (and for camel hair cloth). It is a widely used brush in art, but is considered inferior to the more expensive sable and ox-hair brushes. In some niche applications, such as pinstriping, camel hair is an ideal brush. Camel-hair brushes have numerous uses outside of art, particularly dusting where a soft brush is needed for delicate objects or skin.

Spirou & Fantasio (French: Spirou et Fantasio), commonly shortened to Spirou, is one of the most popular classic Franco-Belgian comics. The series, which has been running since 1938, shares many characteristics with other European humorous adventure comics like The Adventures of Tintin, Lucky Luke, and Asterix. It has been written and drawn by a succession of artists.

Spirou and Fantasio are the series' main characters, two adventurous journalists who run into fantastic adventures, aided by Spirou's pet squirrel Spip and their inventor friend, the Count of Champignac.

Prairie dogs (genus Cynomys) are herbivorous burrowing ground squirrels native to the grasslands of North America. There are five recognized species of prairie dog: black-tailed, white-tailed, Gunnison's, Utah, and Mexican prairie dogs. In Mexico, prairie dogs are found primarily in the northern states, which lie at the southern end of the Great Plains: northeastern Sonora, north and northeastern Chihuahua, northern Coahuila, northern Nuevo León, and northern Tamaulipas. In the United States, they range primarily to the west of the Mississippi River, though they have also been introduced in a few eastern locales. They are also found in the Canadian Prairies. Despite the name, they are not actually canines; prairie dogs, along with the marmots, chipmunks, and several other basal genera belong to the ground squirrels (tribe Marmotini), part of the larger squirrel family (Sciuridae).

Prairie dogs are considered a keystone species, with their mounds often being used by other species. Their mound-building encourages grass development and renewal of topsoil, with rich mineral and nutrient renewal in the soil, which can be crucial for soil quality and agriculture. They are extremely important in the food chain, being important to diets of many animals such as the black-footed ferret, swift fox, golden eagle, red tailed hawk, American badger, and coyote. Other species, such as the golden-mantled ground squirrel, mountain plover, and the burrowing owl, also rely on prairie dog burrows for nesting areas. Grazing species, such as plains bison, pronghorn, and mule deer, have shown a proclivity for grazing on the same land used by prairie dogs, with their regeneration of topsoil being important for maintaining healthy humus. Prairie dogs have some of the most complex systems of communication and social structures in the animal kingdom.

Flying squirrels (scientifically known as Pteromyini or Petauristini) 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.

Molecular studies have shown that flying squirrels are monophyletic (having a common ancestor with no non-flying descendants) and originated some 18–20 million years ago. The genus Paracitellus is the earliest lineage to the flying squirrel dating back to the late Oligocene era. Most are nocturnal and omnivorous, eating fruit, seeds, buds, flowers, insects, gastropods, spiders, fungi, bird's eggs, tree sap and young birds. The young are born in a nest and are at first naked and helpless. They are cared for by their mother and by five weeks are able to practice gliding skills so that by ten weeks they are ready to leave the nest.

The calybium (pl.: calybia) and the cupule make up the accessory fruit of flowering plants in the family Fagaceae. These two parts derive from different flower components.

The cupule holds and protects the fruit during its growth and maturation. In some genera (e.g. Lithocarpus, Quercus), it only partly encloses the single nut, while in others (e.g. Castanea, Fagus), it fully encloses the two or more nuts, and splits open at maturity into four valves to release the nuts. It is derived from the vegetative part of the flower (its attachment to the rest of the plant). It is covered by numerous scales. In some (e.g. Castanea), the scales are developed into sharp spines, giving the nut protection from squirrels and other seed predators, while in others (e.g. most Quercus), they are not. In Lithocarpus, the cupule is very hard and bone-like in texture.

In Norse mythology, Ratatoskr (Old Norse, generally considered to mean "drill-tooth" or "bore-tooth") is a squirrel who runs up and down the world tree Yggdrasil to carry messages between the eagles perched atop it and the serpent Níðhöggr who dwells beneath one of the three roots of the tree. Ratatoskr is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson.

A mousetrap is a specialized type of animal trap designed primarily to catch and, usually, kill mice. Mousetraps are usually set in an indoor location where there is a suspected infestation of rodents. Larger traps are designed to catch other species of animals, such as rats, squirrels, and other small rodents. Trap types differ significantly in effectiveness, potential harm to wildlife and pets, and the level of suffering caused, with some raising serious welfare and environmental concerns.

Purgatorius is a genus of seven extinct eutherian species typically believed to be the earliest example of a primate or protoprimate, a primatomorph precursor to the Plesiadapiformes, dating to as old as 66 million years ago. The first remains (P. unio and P. ceratops) were reported in 1965, from what is now eastern Montana's Tullock Formation (early Paleocene, Puercan), specifically at Purgatory Hill (hence the animal's name) in deposits believed to be about 63 million years old, and at Harbicht Hill in the lower Paleocene section of the Hell Creek Formation. Both locations are in McCone County, Montana.

They have also been found in the Ravenscrag Formation and widely discovered in the early Paleocene Bug Creek Group, along with leptictids. These deposits were once thought to be late Cretaceous, but it is now clear that they are Paleocene channels with time-averaged fossil assemblages. It is thought to have been rat-sized (6 in (15 cm) long and 1.3 ounces (about 37 grams)) and a diurnal insectivore, which burrowed through small holes in the ground. In life, it would have resembled a squirrel or a tree shrew (most likely the latter, given that tree shrews are one of the closest living relatives of primates, and Purgatorius is considered to be the progenitor to primates). The oldest remains of Purgatorius date back to ~65.921 mya, or between 105 thousand to 139 thousand years after the K-Pg boundary.

Ground squirrels are rodents of the squirrel family (Sciuridae) that generally live on the ground or in burrows, rather than in trees like the tree squirrels. The term is most often used for the medium-sized ground squirrels, as the larger ones are more commonly known as marmots (genus Marmota) or prairie dogs, while the smaller and less bushy-tailed ground squirrels tend to be known as chipmunks (genus Tamias).

Together, they make up the "marmot tribe" of squirrels, Marmotini, a clade within the large and mainly ground squirrel subfamily Xerinae, and containing six living genera. Well-known members of this largely Holarctic group are the marmots (Marmota), including the American groundhog, the chipmunks, the susliks (Spermophilus), and the prairie dogs (Cynomys). They are highly variable in size and habitus, but most are remarkably able to rise up on their hind legs and stand fully erect comfortably for prolonged periods. They also tend to be far more gregarious than other squirrels, and many live in colonies with complex social structures. Most Marmotini are rather short-tailed and large squirrels. At up to 8 kg (18 lb) or more, certain marmots are the heaviest squirrels.

The Mexican prairie dog (Cynomys mexicanus) is a diurnal burrowing rodent native to north-central Mexico. It is classified as a keystone species due to its large impact on other species and the environment. Treatment as an agricultural pest has led to its status as an endangered species. They are closely related to squirrels, chipmunks, and marmots. Cynomys mexicanus originated about 230,000 years ago from a peripherally isolated population of the more widespread Cynomys ludovicianus.

Marmots are large ground squirrels in the genus Marmota, with 15 species living in Asia, Europe, and North America. These herbivores are active during the summer, when they can often be found in groups, but are not seen during the winter, when they hibernate underground. They are the heaviest and largest members of the squirrel family.

Chipmunks are small, striped squirrels of subtribe Tamiina. Chipmunks are found in North America, with the exception of the Siberian chipmunk which is found primarily in Asia.

The American badger (Taxidea taxus) is a North American badger similar in appearance to the European badger, although not closely related. It is found in the western, central, and northeastern United States, northern Mexico, and south-central Canada to certain areas of southwestern British Columbia.

The American badger's habitat is typified by open grasslands with available prey (such as mice, squirrels, and groundhogs). The species prefers areas such as prairie regions with sandy loam soils where it can dig more easily for its prey.