| Rodentia Temporal range: Paleocene – Today | |
|---|---|
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| Art of group of Josephoartigasia monesi by Márcio Castro | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| clade: | Mammalia |
| Order: | Rodentia |
Rodentia is an order of mammals, referred to as rodents, that originated in the Paleocene and live to this day. They are native to all continents except Antarctica, and refer to all mammals with a single pair of continuously growing incisor teeth. Famous extant members of Rodentia include mice, rats, porcupines, beavers, and guinea pigs. Popular extinct rodents include Castoroides and Josephoartigasia.
Rodents are one of the most numerous mammal species today, making up approximately 40% of all mammal species. As such, they are also one of the most diverse orders with several unique niches, morphologies, and diets.
Description[]
Rodents are unique from other orders of mammals in multiple ways, but the main characteristic is their dentition, most notably sharp incisors that don't stop growing. The continuous growth of these teeth requires the animal to eat foods that will wear them down, while the shearing of chewing between the incisors will keep them sharp. Most lack canine teeth as well and only possess their incisors and molars. In some species, these molars continuously grow as well. This gap in the teeth is filled with fleshy cheeks to protect the inner mouth. Because of their need to constantly gnaw, their muscles to chew are proportionally some of the strongest in Mammalia, but due to the shape of their skull, they can only either bite or chew at one time.
Rodents have among the smallest mammals known, with only Eulipotyphlans (shrews, moles, hedgehogs, etc.) and Chiropterans (bats) having members that are lighter. Most rodents are small, with a stout build and short limbs, but some did reach large sizes. The current largest living species is the Greater Capybara (Hydrochoerus hydrochaeris), but they did reach larger sizes in prehistory, such as the genus Josephoartigasia with an estimated mass of 500 kg (1,100 lbs) and a length of at least 7 feet.
Rodents are also well known for their heightened senses such as smell, hearing, and vision, along with possessing whiskers for further intake of environmental information, much like cats. Nocturnal species often have much larger eyes and ears, and can see well in areas with very little light.
Classification[]
Rodents are mammals under the clade Glires, forming a sister taxon with the clade Lagomorpha (rabbits, hares, and pikas). Because lagomorphs also have continuous growth of their incisors, they were originally lumped into the order Rodentia until they were separated on the grounds of difference in dentition, as lagomorphs have 2 pairs of incisors unlike rodents. As such, rabbits make the closest living relatives to modern rodents. Further classification of rodents can be difficult, with many filling the same niches and sharing parallel body plans.
There are currently 5 suborders under the order Rodentia, all of which are still extant and diverse.
- Sciuromorpha: the most basal of rodent suborders, and includes dormice, all types of squirrels, and the single species of mountain beaver. Houses 3 extant and 3 extinct families. Not many extinct sciuromorphs are famous, but notable examples include the horned gopher and the giant dormouse Leithia.
- Hystricomorpha: a suborder with several definitions, but includes mole rats, porcupines, chinchillas, capybaras, and nutrias. The inclusion of Caviomorpha, capybaras and chinchillas, is up for debate whether they are true rodents, but are generally considered Hystricomorphs.
- Castorimorpha: most well known for its beavers and kangaroo rats, but also house pocket gophers. Extinct beavers like Castoroides and Castor californicus are its most well known extinct taxa.
- Anomaluromorpha: sometimes regarded as a suborder or infraorder, is the smallest of the 5 clades. Includes springhares and scaly-tailed flying squirrels. One extinct family exists, being Parapetidae. One basal extinct genera is placed in this order as well, named Diatomys.
- Myomorpha: the largest order of rodents, which includes mice, rats, voles, hamsters, and lemmings.