Rodent Facts: The Ultimate Guide To The Order Rodentia
As the old saying goes, you’re never more than six feet away from a rat, and there is probably some truth in that statement; rodents–the group of mammals that includes rats and mice–are a hugely successful group of animals. Rodents are found–often in large numbers–in a wide range of habitats and on every continent except Antarctica.
On this page, you’ll find rodent facts and information that will provide you with an excellent introduction to these fascinating animals…
Rodent Facts: The Ultimate Guide To The Order Rodentia: Page Index
- What Is A Rodent
- Characteristics Of Rodents
- Rodent Diversity
- Types Of Rodents
- Rodent Classification
- Rodent Families
- Other Rodent Characteristics
- Size
- Diet
- Activity
- Locomotion
- Social Behavior And Reproduction
- Rodent Evolution
- Rodents And Human
- Rodent Facts Further Reading
What Is A Rodent?
A rodent is a mammal in the order Rodentia. Familiar rodents include mice, rats, squirrels, beavers, porcupines, and hamsters.
Most rodents are small animals. Although the largest rodent, the capybara, is around the size of a medium-sized dog, most are much smaller.
Characteristics of Rodents
Rodents are mammals, and therefore possess characteristics common to all mammals. These include: having hair, being warm-blooded, having four limbs, and (in female mammals) producing milk to feed their young.
- You can find out more about mammals on this page: Mammals: The Ultimate Guide
The name “rodent” comes from the Latin word “order”, which means to gnaw; all rodents are gnawing animals. Many of the characteristics that separate rodents from other mammals are related to gnawing.
Although rodents can vary greatly in appearance, all show remarkable similarities in the structure of their skulls and teeth.
Rodents have a pair of very large incisor teeth in both the upper and lower jaws. These are the teeth used for gnawing. A rodent’s incisors are unusual in that they continue to grow throughout the rodent’s lifetime. This is vitally important for an animal that spends much of its life chewing on seeds, nuts, and other tough plant material.
When a rodent gnaws, it grinds the top and bottom incisors against one another, resulting in the teeth becoming honed as sharp as chisels – ideal tools for biting.
Another unusual characteristic of rodents is that they lack canine teeth and some of the premolars. Instead, they have a gap (known as a “diastema”) between the incisors and the molars.
In some species, this gap allows food to pass from the sides of the mouth and into cheek pouches for storage. In others, the toothless area is covered by a fold of skin from the upper lip. This allows the animal to move undigestible items (such as bits of a nutshell) out of its mouth while continuing to gnaw on the digestible food inside.
Rodents have specialized musculature on their skulls that enables them to operate their unusual teeth in efficient ways.
Anyone who has watched a squirrel eating a nut will be aware of just how skilled (and fast) these animals are at getting to the edible parts inside!
Rodent Diversity
There are around 2,500 rodent species. In terms of the number of species, the order Rodentia is the largest mammalian order.
An incredible 40 to 50% of all mammal species are rodents, and there are almost twice as many rodents as there are bats, which make up the next-largest mammalian order.
- Confused about terms such as “order” and “family”? Check out this guide to Animal Classification
Rodents live on every continent except Antarctica. Their various adaptations have made them successful in most terrestrial habitats, from deserts to arctic tundra.
Types of Rodents
Types of rodents include mice, rats, squirrels, porcupines, beavers, guinea pigs, capybaras, and naked mole rats. The order Rodentia is divided into 5 suborders and around 30 families.
Rodent Suborders
- Myomorpha includes mice, rats, hamsters, lemmings, voles, gerbils, jerboas, muskrats, and water rats.
- Sciuromorpha includes squirrels, dormice, chipmunks, prairie dogs, and marmots.
- Hystricomorpha includes porcupines, agoutis, molerats, cane rats, capybaras, guinea pigs, cavies, chinchillas, and coypus.
- Castorimorpha includes beavers, kangaroo rats, kangaroo mice, and gophers.
- Anomaluromorpha includes scaly-tailed flying squirrels and spring hares, all found only in Africa.
Rodent Families
Among the more familiar rodent families are Sciuridae (squirrels and related animals); Caviidae (guinea pigs, capybaras, wild cavies, and related animals); Castoridae (beavers); and Muridae (mice, rats, and related animals).
Muridae (whose members are known as “murids”) represents more than 1,100 species; almost half of all rodents. This means that around a quarter of all mammal species are either mice, rats, hamsters, voles, muskrats, lemmings, gerbils, or other murids.
Rodent classification is complex and ongoing; the grouping of rodents is liable to change as we learn more about rodents and the animal kingdom in general.
Other Characteristics of Rodents
Size
In general, rodents are not large animals; most weigh less than 6.5 lbs (3 kg).
The largest extant (living) species is the capybara (Hydrochoerus hydrochaeris) of South America. Adults of this species can reach 146 lbs (66 kg), with a body length of up to 53 in (135 cm).
In contrast, the smallest rodent is the pygmy jerboa (Salpingotulus michaelis), a species native to the hot, sandy deserts of Pakistan. It has a mass of about 0.2 oz (5 g) and a body length of 2 in (5 cm), excluding its very long tail.
Diet
Rodents are mostly herbivorous, eating seeds, bark, leaves, and fruit, although many will also feed on insects at times.
Grasshopper mice (found in the USA and Mexico) are carnivorous, feeding on insects, spiders, worms, and even snakes.
The rats and mice that live in association with human settlements are notoriously omnivorous and will eat almost anything they come across.
Activity
Rodents show a variety of activity patterns, with some being diurnal (active during the daytime), while others are nocturnal.
Nocturnal rodents are characterized by having very large eyes, which provide improved night vision.
Many rodents hibernate during the winter. Some species of chipmunks, dormice, squirrels and prairie dogs sleep for between 5 and 8 months of each year; during hibernation their body temperatures and metabolic rates decrease, thereby reducing their need for food.
The Arctic ground squirrel (Urocitellus parry) hibernates through the winter months. While hibernating its body temperature can get as low as 28.6oF (-3oC).
Many desert species, in addition to hibernating during the winter, have a daily pattern of dormancy, sleeping in their burrows during the heat of the day and only emerging at night. This low-energy lifestyle allows them to survive on food with low nutritional value.
Locomotion
As well as the familiar scurrying movement of mice and rats, rodents employ many other forms of locomotion.
The elongated hind limbs of jerboas, gerbils, kangaroo rats, and springhares allow them hop at break-neck speeds over desert flats.
Arboreal (tree-dwelling) rodents such as squirrels determine and tree voles have sharp claws for climbing trees.
Another group of arboreal rodents, the flying squirrels, have a furry membrane of skin between their forelegs and hindlegs. This acts as a parachute, allowing them to glide from tree to tree.
Water rats, coypus, muskrats, and beavers are rodents whose primary form of locomotion is swimming. They have thick, water4proof coats and many species are equipped with webbed feet and thick tails for moving through the water.
Although many rodents are excellent burrowers, the molerats of the African continent must surely take the digging prize. These strange fossorials (burrowing) rodents are, confusingly, neither moles nor rats. Instead, they belong to their own family, Bathyergidae.
Molerats have cylindrical bodies, hardly any neck, tiny (almost blind) eyes, and no external ears; all are adaptations for moving around underground. The molerat excavates its tunnels using its enormous, protruding incisors – literally gnawing its way through the ground.
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