The order Rodentia, containing > 2,000 living species placed in 28 families (approximately half of all mammalian species), is the largest order of mammals. Rodents are found worldwide, except in Antarctica and on some oceanic islands.
Ecologically, rodents are remarkably diverse. Some species spend their entire lives above the ground in the canopy of rainforests; others rarely emerge from beneath the ground. Some species are aquatic; others are equally specialized for life in deserts.
Many rodents are omnivorous to some degree. Others are highly specialized—for example, eating only a few species of invertebrates or fungi.
Despite their morphological and ecological diversity, all rodents share one characteristic: a highly specialized dentition for gnawing. Rodents have one pair each of upper incisors and lower incisors. Between each incisor and the first cheek tooth is a toothless interval called the diastema.
A rodent's incisors are rootless and grow continuously. Enamel is deposited on the anterior and lateral incisor surfaces; the posterior incisor surface is dentin. During gnawing, as the incisors chisel against each other, they wear away the softer dentin, leaving a sharp enamel edge. This self-sharpening system is very effective and is one of the keys to the enormous ecological success of rodents.
Using the incisors together to chisel away at a surface requires muscular action that forcefully brings the lower jaw forward. The masseter muscle does this in rodents. Historically, rodents have been divided into three groups according to how the masseter attachments evolved: sciuromorphs (eg, squirrels, beavers), hystricomorphs (eg, New and Old World porcupines, guinea pigs, jerboas), and myomorphs (eg, New and Old World rats and mice, hamsters, gerbils, voles).
Most modern rodents have adapted to eat seeds—a behavior that links them to the evolution of modern grasses. All rodents evolved from shrewlike carnivorous or insectivorous ancestors and have since diverged into various families and subfamilies.
Despite the large number of rodents, only a few species are owned as pets. The common pet rodents are chinchillas, degus, gerbils, guinea pigs (see separate Guinea Pigs chapter), hamsters, mice, and rats. Less common pet rodents are African giant pouched rats, prairie dogs, spiny mice, and voles.
For the key biological characteristics of rodents that are the most common pets, see the table .
Biological Data of Pet Rodentsa
Chinchilla | Degu | Gerbil | Guinea Pig | Hamster | Mouse | Rat | |
|---|---|---|---|---|---|---|---|
Lifespanb (years) | 4–15 | 5–8 | 2.5–4 | 4–8 | 1–2 | 1–2 | 2–3 |
Adult male body weight (g) | 400–500 | 170–300 | 45–130 | 800–1,600 | 85–140 | 20–30 | 300–500 |
Adult female body weight (g) | 400–600 | 170–350 | 55–135 | 700–1,300 | 95–120 | 18–35 | 200–325 |
Age at sexual maturity (weeks) | 32–36 | 16–24 | 9–12 | 10–12 | 4–7 | 6–8 | 6–8 |
Length of gestation (days) | 111 | 87–92 | 24–26 | 63–69 | 16 | 19–21 | 21–23 |
Litter size (average) | 2 | 4–10 | 1–12 | 3–4 | 6–10 | 5–12 | 6–13 |
Age at weaning (days) | 42–56c | 21–28 | 21 | 30c | 21–30 | 21–23 | 21 |
a All data from Quesenberry KE, Orcutt CJ, Mans C, Carpenter JW, eds. Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery. 4th ed. Elsevier; 2021. b Lifespan data are for typical lifespan ranges in pet rodents. Lifespans exceeding these times have been recorded for rodents in research studies. c Chinchillas and guinea pigs have precocious young that can eat some solid food at 7–14 days. Early weaning results in lower body weight and social maladaptation in later life. | |||||||
As prey animals, rodents do not show obvious signs of pain or disease until near death. Consequently, sick rodents are often presented late in disease progression, when the prognosis is more guarded.
Common diseases of pet rodents include dental disease (1), respiratory disease (2), and dermatological disease. Traumatic injuries are also common in rodents and occur at all ages.
Although some diseases in rodents are caused by shortcomings in husbandry, often rodents subjected to “benign neglect” live long, healthy lives. Overfeeding pet rodents can contribute to the early development of many spontaneous tumors and degenerative diseases.
For More Information
Rodent Jaws. Animal Diversity Web.
See pet owner content regarding chinchillas, gerbils, guinea pigs, hamsters, mice, and rats.
References
Minarikova A, Hauptman K, Jeklova E, Knotek Z, Jeki V. Diseases in pet guinea pigs: a retrospective study in 1000 animals. Vet Rec. 2015;177(8):200. doi:10.1136/vr.103053
Rey F, Bulliot C, Bertin N, Mentré V., REMORA Team. Morbidity and disease management in pet rats: a study of 375 cases. Vet Rec. 2015;176(15):385. doi:10.1136/vr.102728
