Rodents (meaning “to gnaw”) are mammals of the order Rodentia. They are characterized by upper and lower pairs of continuously growing rootless incisor teeth. Rodents are the largest group of mammals, constituting almost 40% of the class Mammalia. They are found in vast numbers on all continents except Antarctica, New Zealand, and a few Arctic and other oceanic islands, although some species have been introduced even to those places through their association with humans.
Encompassing 27 separate families, Rodents include not only the Family Muridae (“true” rats and mice) but also such diverse groups as porcupines, beavers, squirrels, marmots, pocket gophers, and chinchillas.
All rodents possess constantly growing rootless incisors that have a hard enamel layer on the front of each tooth and softer dentine behind. The differential wear from gnawing creates perpetually sharp chisel edges.
The nature of the jaw articulation ensures that incisors do not meet when food is chewed and that upper and lower cheek teeth (premolars and molars) do not make contact while the animal gnaws.
The range in body size of rodents between the mouse (wt. 18 gms, length 12 cm) and the marmot (wt. 3000 gms, length 50 cm) spans the majority of living rodents, but the extremes are remarkable.
The smallest on record is Delany’s swamp mouse (Delanymys brooksi), associated with bamboo in the marshes and mountain forests in Africa.
- Weight: 5 to 7 grams
- Length: 5 to 6 cm.
The largest is the capybara (Hydrochoerus hydrochaeris) of Central and South America.
- Weight: 35 to 66 kg
- Length: 100 to 135 cm.
Some extinct species were even larger, attaining the size of a black bear or small rhinoceros.
The largest rodent ever recorded, Josephoartigasia monesi, lived some 2 to 4 million years ago, by some estimates it grew to a length of about 3 metres (10 feet) and weighed nearly 1,000 kg.
Rodents species can be arboreal, fossorial (burrowing), or semi-aquatic. These species include mice, rats, squirrels, prairie dogs, chipmunks, chinchillas, porcupines, beavers, guinea pigs, hamsters, gerbils and capybaras.
Rabbits, hares, and pikas were once considered a part of order Rodentia. But are now considered to be in a separate order, the Lagomorpha. Nonetheless, Rodentia and Lagomorpha are sister groups, sharing a single common ancestor and forming the clade of Glires.
Rodents are the most diversified mammalian order and live in a variety of terrestrial habitats, including human-made environments. Also rodents reached both South America and Madagascar from Africa and without human intervention, they’re the only terrestrial placental mammals to have colonized Australia and New Guinea.
Rodents have adapted to almost every terrestrial habitat, from cold tundra (where they can live under snow) to hot deserts. Humans have also allowed the animals to spread to many remote oceanic islands (e.g., the Polynesian rat).
The rodent fossil record dates back to the Paleocene on the supercontinent of Laurasia. Rodents greatly diversified in the Eocene, as they spread across continents, sometimes even crossing oceans.
Rodents' Behavior and life
Rodents tend to be social animals. Most species live in societies with complex ways of communicating with each other. Among them, mating can vary from monogamy, to polygyny, to promiscuity. Many have litters of underdeveloped, altricial young, while others are precocial at birth.
Rodents mostly are herbivores, feeding exclusively on plant material such as seeds or other plant material, but some are omnivorous and a few are predators, having more variations in their diets including insects, fish, or meat. They all use their sharp incisors to gnaw food, excavate burrows, and defend themselves. A functional-morphological study of the rodent tooth system supports the idea that primitive rodents were omnivores rather than herbivores.
Rodents Relation to Humans
Importance to Humans
- Rodents provide a source of food through hunting and husbandry (e.g., cavy, cane rat, bamboo rat, paca, capybara, and woodchuck).
- Apparel is derived from their fur (e.g., nutria and chinchilla).
- They are used in medical sciences for biomedical and genetic research (especially mice and rats).
- Also they can give detailed insight on mammalian biology and evolutionary history.
- They can become pleasure as household pets (e.g., golden hamster, guinea pig, and gerbil).
Threat to Humans
- Rodents certain species are reservoirs for diseases such as plague, murine typhus, scrub typhus, tularemia, rat-bite fever, Rocky Mountain spotted fever, and Lassa fever, among others.
- Worldwide, rats and mice spread over 35 diseases to humans directly and indirectly as well.
- In particular, the brown rat, the black rat, and the house mouse, are serious pests, eating, contaminating, and spoiling food stored by humans and spreading diseases.
- They damage the crops before harvest.
- Due to their burrowing water-impounding structures gets leaked.
- Also their gnawing damages the objects.