Archive article, written 2009–2016. Not yet reviewed by a veterinarian. About our articles
| Characteristics of rodents |
| Characteristics: Many rodents are small; the tiny African pygmy mouse can be only 6 cm (2.4 in) in length and 7 g (0.25 oz) in weight at maturity, and the Baluchistan Pygmy Jerboa is of roughly similar or slightly smaller dimensions. On the other hand, the capybara can weigh up to 80 kg (180 lb), and the largest known rodent, the extinct Josephoartigasia monesi, is estimated to weigh about 1,000 kg (2,200 lb), and possibly up to 1,534 kg (3,380 lb) or 2,586 kg (5,700 lb). Rodents have two incisors in the upper as well as in the lower jaw which grow continuously and must be kept worn down by gnawing; this is the origin of the name, from the Latin rodere, to gnaw. These teeth are used for cutting wood, biting through the skin of fruit, or for defense. The teeth have enamel on the outside and exposed dentine on the inside, so they self-sharpen during gnawing. Rodents lack canines, and have a space between their incisors and premolars. Nearly all rodents feed on plants, seeds in particular, but there are a few exceptions which eat insects or fish. Some squirrels are known to eat passerine birds like cardinals and blue jays. Typical rodent tooth system Rodents are important in many ecosystems because they reproduce rapidly, and can function as food sources for predators, mechanisms for seed dispersal, and as disease vectors. Humans use rodents as a source of fur, as pets, as model organisms in animal testing, for food, and even for detecting landmines. Members of non-rodent orders such as Chiroptera (bats), Scandentia (treeshrews), Insectivora (moles, shrews and hedgehogs), Lagomorpha (hares, rabbits and pikas) and mustelid carnivores such as weasels and mink are sometimes confused with rodents. While there is a broad range of characteristics among the families, the feature that sets rodents apart from other family members is their teeth. Rodents have one pair of upper incisors (the chisel-shaped teeth at the front of the mouth), and one pair of lower incisors. These teeth grow continually throughout their life. The outer surfaces of the incisors have a thick enamel (hard white substance) layer. Behind the incisors is a large gap in the tooth rows. There are no canines, spade-shaped teeth located next to the incisors. Typically there are only a few molars at the rear of the jaws. The number of teeth rarely is more than twenty-two. |
| The name Rodentia
comes from the Latin verb rodere meaning to gnaw, a name suitable for a
rodent that is constantly gnawing! Rodents' incisor teeth grow
throughout their life and they grind their incisor teeth together to
wear them down. If for some reason the rodent is unable to wear its
incisors down, the tips may grow past each other and continue to grow
outward into spiral. This may result in the upper teeth piercing the
roof of the mouth, and the lower teeth growing upward in front of the
nose, which could kill the animal. In general, rodents have a compact body with short legs. They typically have four to five digits on each of the front feet and three to five digits on the rear feet. Generally, the sole of the foot is bare. Some rodents, such as hamsters and pocket gophers, have cheek pouches, which allow the animals to store and transport food. The tails of some rodent species break off when these animals are caught by the tail, which allows them to escape. The tail will partially grow back. Other physical characteristics of rodents vary widely depending upon the species and where it lives. For example, rodents that live in the desert, such as American kangaroo rats, Australian hopping mice, and north African jerboas, have long, narrow hind legs and feet with a long tail used for hopping over the sandy desert floor. They all have well-developed hearing, small front limbs, and pale coloration. Animals that live in and around the water, such as the capybara and beaver, may have webbed or partially webbed feet and tails modified for swimming. |