Hamster in the context of "Rodents"

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 pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive/cute appearances, intelligence, and relatable personalities, but some pets may be taken in on an altruistic basis (such as a stray animal) and accepted by the owner regardless of these characteristics.

Two of the most popular pets are dogs and cats. Other animals commonly kept include rabbits; ferrets; pigs; rodents such as gerbils, hamsters, chinchillas, rats, mice, and guinea pigs; birds such as parrots, passerines, and fowls; reptiles such as turtles, lizards, snakes, and iguanas; aquatic pets such as fish, freshwater snails, and saltwater snails; amphibians such as frogs and salamanders; and arthropod pets such as tarantulas and hermit crabs. Smaller pets include rodents, while the equine and bovine group include the largest companion animals.

Cecotropes (also caecotropes, cecotrophs, caecotrophs, cecal pellets, soft feces, or night feces) are a nutrient-filled package created in the gastrointestinal (GI) tract that is expelled and eaten by many animals (such as rabbits, guinea pigs, mice, hamsters, and chinchillas) to obtain more nutrients out of their food. When food passes through the GI tract the first time, the stomach and the small intestine digest the food material, which then moves into the colon, where the food particles are sorted by size. The smaller particles of fiber are moved into the cecum where they are fermented by microbes. This creates useable nutrients which are stored and expelled in cecotropes. The nutrients from the cecotropes are absorbed in the small intestine. The nutrients gained from cecotrophy include short-chain fatty acids, vitamin B, sodium, potassium, amino acids, and protein.

Lagomorphs (a grouping including rabbits, hares, and pikas) are perhaps the most well-known for producing and eating cecotropes, but other monogastric fermenters, such as rodents, also produce cecotropes. Rodents including beavers, guinea pigs, mice, hamsters, and chinchillas are known cecotrophs. Other animals also eat cecotropes, such as the common ringtail possum and the coppery ringtail possum.

Rodents have been employed in biomedical experimentation from the 1650s. Rodent studies up to the early 19th century were mainly physiological or toxicological. The first rodent behavioral study was carried out in 1822, a purely observational study, while quantitative rodent behavioral testing began in the late 19th century. Currently, rodents are commonly used in animal testing for physiological, pathological and behavioral scientific studies, particularly mice and rats, but also guinea pigs, hamsters, gerbils and others. Mice are the most commonly used vertebrate species, due to their availability, size, low cost, ease of handling, and fast reproduction rate.

The domestication of small mammals to keep as pets is a relatively recent development, arising only after large-scale industrialization. Historically, Western society was more agrarian than today, with rodents as a whole seen as vermin that were carriers for disease and a threat to crops. Animals that hunted such pests, such as terriers, ferrets and cats, were prized.

Many small animals kept as household pets are rodents, including: fancy mice, fancy rats, hamsters (golden hamsters and dwarf hamsters), gerbils (Mongolian jirds and duprasi gerbils), common degus, common chinchillas, and guinea pigs (cavies). Non-rodents, including rabbits, hedgehogs and sugar gliders, are also kept.

The Muroidea are a large superfamily of rodents, including mice, rats, voles, hamsters, lemmings, gerbils, and many other relatives. Although the Muroidea originated in Eurasia, they occupy a vast variety of habitats on every continent except Antarctica. Some authorities have placed all members of this group into a single family, Muridae, due to difficulties in determining how the subfamilies are related to one another. Many of the families within the Muroidea superfamily have more variations between the families than between the different clades. A possible explanation for the variations in rodents is because of the location of these rodents; these changes could have been due to radiation or the overall environment they migrated to or originated in. The following taxonomy is based on recent well-supported molecular phylogenies.

The muroids are classified in six families, 19 subfamilies, around 280 genera, and at least 1,750 species.