These incisors have thick layers of enamel on the front and little enamel on the back. The distinguishing feature of the rodents is their pairs of continuously growing, razor-sharp, open-rooted incisors. The act of chewing wears down the dentine, leaving a sharp, chisel-like edge. Accidentally introduced species of rodents are often considered to be invasive and have caused the extinction of numerous species, such as island birds, the dodo being an example, previously isolated from land-based predators.Ĭharacteristics Drawing of typical rodent tooth system: The front surface of the incisors is hard enamel, whereas the rear is softer dentine. Some species, in particular, the brown rat, the black rat, and the house mouse, are serious pests, eating and spoiling food stored by humans and spreading diseases. Rodents have been used as food, for clothing, as pets, and as laboratory animals in research. Rodents reached both South America and Madagascar from Africa and, until the arrival of Homo sapiens, were the only terrestrial placental mammals to reach and colonize Australia. Rodents greatly diversified in the Eocene, as they spread across continents, sometimes even crossing oceans. The rodent fossil record dates back to the Paleocene on the supercontinent of Laurasia. Many have litters of underdeveloped, altricial young, while others are precocial (relatively well developed) at birth. Mating among rodents can vary from monogamy, to polygyny, to promiscuity. They tend to be social animals and many species live in societies with complex ways of communicating with each other. Most eat seeds or other plant material, but some have more varied diets. They use their sharp incisors to gnaw food, excavate burrows, and defend themselves. Most rodents are small animals with robust bodies, short limbs, and long tails. Nonetheless, Rodentia and Lagomorpha are sister groups, sharing a single common ancestor and forming the clade of Glires. Rabbits, hares, and pikas, who also have incisors that grow continuously (but have two pairs of upper incisors instead of one), were once included with them, but are now considered to be in a separate order, the Lagomorpha. Well-known rodents include mice, rats, squirrels, prairie dogs, porcupines, beavers, guinea pigs, and hamsters. However, all rodents share several morphological features, including having only a single upper and lower pair of ever-growing incisors. Species can be arboreal, fossorial (burrowing), saltatorial/richochetal (leaping on their hind legs), or semiaquatic. Rodents are extremely diverse in their ecology and lifestyles and can be found in almost every terrestrial habitat, including human-made environments. They are native to all major land masses except for New Zealand, Antarctica, and several oceanic islands, though they have subsequently been introduced to most of these land masses by human activity. About 40% of all mammal species are rodents. Rodents (from Latin rodere, 'to gnaw') are mammals of the order Rodentia ( / r oʊ ˈ d ɛ n ʃ ə/), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. Combined range of all rodent species (not including introduced populations)
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