Difference between revisions of "Rodent" - New World Encyclopedia

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{{Taxobox
 
{{Taxobox
 
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| phylum = [[Chordata]]
 
| phylum = [[Chordata]]
 
| classis = [[Mammal]]ia
 
| classis = [[Mammal]]ia
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| subclassis = [[Eutheria]]
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| subclassis = Eutheria
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| unranked_ordo = [[Euarchontoglires]]
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| unranked_ordo = Euarchontoglires
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| superordo = [[Glires]]
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| superordo = Glires
 
| ordo = '''Rodentia'''
 
| ordo = '''Rodentia'''
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| ordo_authority = [[Thomas Edward Bowdich|Bowdich]], 1821
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| ordo_authority = Bowdich, 1821
 
| subdivision_ranks = Suborders
 
| subdivision_ranks = Suborders
 
| subdivision =
 
| subdivision =
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[[Sciuromorpha]]<br>
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Sciuromorpha<br/>
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[[Castorimorpha]]<br>
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Castorimorpha<br/>
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[[Myomorpha]]<br>
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Myomorpha<br/>
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[[Anomaluromorpha]]<br>
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Anomaluromorpha<br/>
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[[Hystricomorpha]]
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Hystricomorpha
 
}}
 
}}
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'''Rodents''' are members of the order '''Rodentia''', which is the largest order of [[mammal]]s. Rodents are most distinguished by their [[tooth|teeth]] — the word "rodent" comes from the Latin word ''"rodere"'', meaning "to gnaw."
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'''Rodents''' are members of the order '''Rodentia,''' which is the largest order of [[mammal]]s. Rodents are mostly distinguished by their [[tooth|teeth]]—the word "rodent" comes from the Latin word ''rodere,'' meaning "to gnaw."
  
 +
There are about 1,500 [[species]] of rodents including [[mouse|mice]], [[rat]]s, [[squirrel]]s, and [[beaver]]s (Nowak, 1983; UCMP, 2007). They are found on all continents except [[Antarctica]] and in almost all land habitats, from tropical forests to deserts to mountains to tundras. Rodents and [[bat]]s are the only orders of [[placental mammal]]s with species native to [[Australia]].
  
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There are about 1500 [[species]] of rodents (Nowak 1983, UCMP 2007), including [[mouse|mice]], [[rat]]s, [[squirrel]]s, and [[beaver]]s. They are found on all continents except [[Antartica]] and in almost all land habitats from tropical forests to deserts to mountains and tundras.  
+
While some rodents have a reputation as [[agriculture|agricultural]] pests or vectors of [[disease]], rodents in general provide significant [[ecology|ecological]], [[nutrition|dietary]], aesthetic, and scientific values. In many habitats, they are very abundant, and thus are important in [[food chain|food webs]] and in dispersal of plant [[seed]]s. Some species have provided food and fur to human beings, and the trapping of beavers for fur was historically important in North America. Laboratory rats, mice, and guinea pigs have contributed greatly as model organisms in scientific research.
  
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==Rodent characteristics==
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[[Rabbit]]s, [[hare]]s, and [[pika]]s are not rodents, but members of another order, [[Lagomorpha]].
  
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The incisor teeth of rodents are their most distinctive feature. An rodent's incisors grow continuously thoughout its life and must be kept worn down by gnawing. The incisors have [[tooth enamel|enamel]] on the outside and exposed [[dentine]] on the inside, so they self-sharpen during gnawing.  Rodents lack [[Canine tooth|canines]] and first premolars, which creates a space between their incisors and their grinding teeth.
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==Rodent Characteristics==
  
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Most rodents are small; the tiny African pygmy mouse is one of the smallest rodents and is only 6 cm (2.5 inches) long and weighs 7 grams (.25 oz). The largest living rodent, the [[capybara]] can weigh up to 45 kg (100 pounds) and the extinct ''Phoberomys pattersoni'' is believed to have weighed up to 700 kg (1500 lbs).
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[[Image:Gnagarnas tandsystem, Nordisk familjebok.png|thumb|left|Typical rodent tooth system]]
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The incisor teeth of rodents are their most distinctive feature. A rodent's incisors grow continuously throughout its life and must be kept worn down by gnawing. The incisors of a pocket gopher can grow 20 inches in one year. The incisors have [[tooth enamel|enamel]] on the outside and exposed [[dentine]] on the inside, so they self-sharpen during gnawing. Rodents lack [[Canine tooth|canines]] and first premolars, which creates a space between their incisors and their grinding teeth.
  
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Most rodents mature quickly and soon have offspring.  A female meadow mouse (''Microyus pennsyvanicus'') can have up to 17 litters of 4 to 13 young in a year.  Many rodents have an average life span of only a year or less, although some larger rodents such as beavers and porcupines can live over 20 years. The oldest recorded rodent was a Sumatran crested porcupine (''Hystrix brachyura'') which lived 27 years and 3 months (Voelker 1986).
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Most rodents are small; the tiny African pygmy mouse ''(Mus minutoides)'' is one of the smallest rodents at only 2.5 inches (6 cm) long and weighing only .25 oz (7 grams). The largest living rodent, the [[capybara]] ''(Hydrochoerus hydrochaeris),'' can weigh up to one hundred pounds (45 kg) and the [[extinction|extinct]] ''Phoberomys pattersoni'' is believed to have weighed up to 1,500 pounds (700 kg).
  
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==Rodents in nature==
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Most rodents mature quickly and soon produce offspring. A female meadow mouse ''(Microyus pennsyvanicus)'' can have up to 17 litters of 4 to 13 young in a year.
  
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==Size and range of order==
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Many rodents have an average life span of only a year or less, although some larger rodents such as [[beaver]]s and [[porcupine]]s can live over 20 years. The oldest recorded rodent was a Sumatran Crested Porcupine ''(Hystrix brachyura)'' that lived 27 years and three months (Voelker, 1986).
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In terms of number of [[species]] — although not necessarily in terms of number of organisms (population) or [[Biomass (ecology)|biomass]] — rodents make up the largest order of mammals, with over 40 percent of mammalian species belonging to the order.<ref> {{cite web|last= Myers |first= Phil | date=2000 |url= http://animaldiversity.ummz.umich.edu/site/accounts/information/Rodentia.html |title=Rodentia |work=Animal Diversity Web |publisher=University of Michigan Museum of Zoology |accessdate= 2006-05-25}}</ref>  Their success is probably due to their small size, short breeding cycle, and ability to gnaw and eat a wide variety of foods.(Lambert, 2000)
 
  
 +
==Rodents in Nature==
  
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[[Image:bristol.zoo.capybara.arp.jpg|thumb|left|Capybara, the largest living rodent]]
 +
Most rodents eat [[plant]]s, including [[seed]]s, [[fruit]], [[Grass|grasses]], and [[leaf|leaves]], as well as the bark of [[tree]]s. Some rodents prey on [[insect]]s and other small animals. The fish-eating rats ''(Ichthyomys species)'' of South America (and some others) swim in streams to catch small fish.
 +
 +
The naked mole rat ''(Heterocephalus glaber)'' spends its entire life underground. Flying squirrels live their lives in trees and glide, not truly fly, between trees to avoid spending time on the ground. Many rodents living in colder climates [[hibernation|hibernate]] to conserve energy during the winter.
 +
 +
Some squirrels help maintain and spread forests by burying the seeds of trees. The seeds of the Brazil nut tree will not germinate unless they are first gnawed open and buried by an agouti ''(Dasyprocta species)'' (Attenborough, 2002). Gophers, ground hogs, prairie dogs, and other burrowing rodents enrich the soil by mixing it and by burying vegetation. Beavers ''(Castor species)'' help control flooding and create pond and meadow habitats with their dam building, which benefits many other species,.
  
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==Characteristics==
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Rodents are often the most abundant small [[vertebrate]]s in their habitats and are an important source of food for many other animals, including [[bird]]s, [[reptile]]s, and other [[mammal]]s. If their numbers were not kept in check by predators, rodents would soon over run their environments. Norwegian lemmings ''(Lemmus lemmus),'' and some other rodents, undergo "population explosions" every few years. This is thought to help them expand their range into new areas.
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[[Image:bristol.zoo.capybara.arp.jpg|thumb|left|Capybara, the largest living rodent]]
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 +
==Rodents and Humans==
  
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From earliest times, rodents have been eaten by [[human]]s. Although the flesh of all species is edible, rodents are not an important food source in the world today. Among the exceptions are the [[capybara]] and the [[guinea pig]] ''(Cavia porcellus)'' of [[South America]] and the bandicoot rat ''(Bandicota bengalensis)'' of Southeast [[Asia]]. The [[dormouse]] ''(Glis glis)'' was considered a delicacy in ancient Rome and is still eaten in parts of [[Europe]] today. In [[North America]], [[squirrel]]s, [[groundhog]]s, [[muskrat]]s, and [[porcupine]]s are sometimes eaten.
  
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Nearly all rodents feed on plants, seeds in particular, but there are a few exceptions which eat insects or even fish.
+
The [[fur]] of some rodents is an important product. The trapping of [[beaver]]s for their fur played an important part in the history of North America. Some other rodents are also trapped for fur in the wild, while the chinchilla ''(Chinchilla laniger)'' of South America is raised for its fur.  
  
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Rodents are important in many ecosystems because they reproduce rapidly, and can function as food sources for predators, mechanisms for [[seed dispersal]], and as [[vector (biology)|disease vectors]]. Humans use rodents as a source of [[fur]], as [[model organism]]s in animal testing, for food, and even in detecting [[land mine|landmines]]<ref>{{cite news|first=Michael |last=Wines |url= http://www.theage.com.au/articles/2004/05/18/1084783512636.html |title= Gambian rodents risk death for bananas |work=The Age |publisher= The Age Company Ltd. |date=[[2004-05-19]] |accessdate= 2006-05-25}} "A rat with a nose for landmines is doing its bit for humanity" Cited as coming from the New York Times in the article.</ref>.
+
The greatest impact of rodents on humans began when [[agriculture]] started and people chose to live in settled homes. At that time, some rodent species moved into human dwellings, especially to eat stored grain and food scraps and to benefit from warm living spaces and protection from predators. The house mouse ''(Mus musculus),'' which seems to be native from the Mediterranean area to [[China]], and several species of rats ''(Rattus species),'' native to Southeast Asia, were the most successful and now live with humans all over the world. Although the great majority of rodent species do no harm to humans, these ''[[symbiosis|commensal]]'' (which means "sharing the same table") species, especially rats, do a tremendous amount of damage to crops and stored food. They also spread [[disease]]s, including the [[bubonic plague]], that have killed tens of millions of people through history and are still a danger today.  
  
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Members of non-rodent orders such as ''[[Chiroptera]]'' (bats), ''[[Scandentia]]'' ([[treeshrew]]s), ''[[Insectivora]]'' ([[mole (animal)|mole]]s, [[shrew]]s and [[hedgehog]]s), ''[[Lagomorpha]]'' ([[hare]]s, [[rabbit]]s and [[pika]]s) and [[mustelid]] [[carnivore]]s such as [[weasel]]s and [[mink]] are sometimes confused for rodents.  Rodents have a carrier-immunity to [[rabies]] virus, making them immune to the potentially infectious and lethal disease.  They are carriers for most other animal-to-human illnesses, however, and still should not be agitated.
+
[[Image:MorrisWaterMaze.jpg|thumb|Laboratory rat in a water maze experiment]]
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Rats also do a lot of damage to the environments that they have been introduced to by humans. The black rat ''(Rattus rattus),'' also known as the ship rat, was carried around the world on sailing ships and has contributed to the [[extinction]] of many species of birds and other animals, especially on remote islands (ISSG, 2007). Many wild rodent species and subspecies are now endangered because of habitat loss and introduction of [[invasive species]], including rats (IUCN, 2007).  
  
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== Natural history ==
+
Some species of rodents are kept as [[pet]]s. One of the most popular rodent pets is the golden hamster ''(Mesocricetus auratus).'' All of the world's pet golden hamsters are considered to be descendants of one family captured in [[Syria]] in 1930 (Voelker, 1986). Other rodent pets include mice, rats, and guinea pigs.  
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[[Image:Apodemus sylvaticus.JPG|thumb|left|[[Wood Mouse]]]]
 
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The [[fossil]] record of rodents begins long before the extinction of the [[dinosaur]]s 65 million years ago, as early as the [[Jurassic Period]]. By the end of the [[Eocene epoch]], [[beaver]]s and [[squirrel]]s appeared in the fossil record. They originated in [[Laurasia]], the joined continents of [[North America]], [[Europe]], and [[Asia]]. Some species colonized [[Africa]], giving rise to the earliest [[hystricognath]]s. From there they rafted to [[South America]], an isolated [[continent]] during the [[Oligocene]] and [[Miocene]] epochs. By the [[Miocene]], [[Africa]] collided with [[Asia]], allowing rodents such as [[porcupine]]s to spread into [[Eurasia]]. During the [[Pliocene]], rodent fossils appeared in [[Australia]]. Even though [[marsupial]]s are the prominent mammals in Australia, rodents make up almost 25% of the mammals on the continent. Meanwhile, the Americas became joined and some rodents expanded into new territory; [[Sigmodontinae|mice]] headed south and porcupines headed north.  
 
  
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;Some Prehistoric Rodents
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Rodents also play an important role as subjects of scientific research. One reason for this is that with their short lives many generations can be studied in a few years. Research on mice, rats, and guinea pigs has contributed greatly to our understanding of biological processes and has helped to save millions of human lives.
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:''[[Castoroides]]'', a giant [[beaver]]
 
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:''[[Ceratogaulus]]'', a horned burrowing rodent
 
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:[[Flores Giant Rat]], a rat that grew to a large size on the island of [[Flores]]
 
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:[[Giant hutia]]s, a group of rodents once found in the [[West Indies]]
 
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:''[[Ischyromys]]'', a primitive [[squirrel]]-like rodent
 
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:''[[Leithia]]'', a giant [[dormouse]]
 
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:''[[Neochoerus pinckneyi]]'', a giant North American [[capybara]] that weighed 50 kg
 
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:''[[Phoberomys pattersoni]]'', the largest known rodent
 
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:''[[Telicomys]]'', a giant South American rodent
 
  
 
==Classification==
 
==Classification==
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The rodents are part of the [[clade]]s: [[Glires]] (along with [[Lagomorpha|lagomorphs]]), [[Euarchontoglires]] (along with [[Lagomorpha|lagomorphs]], [[primate]]s, [[treeshrew]]s, and [[colugo]]s), and [[Boreoeutheria]] (along with most other [[Eutheria|placental]] [[mammal]]s).  The order Rodentia may be divided into [[suborder]]s, [[infraorder]]s, [[superfamily|superfamilies]] and [[family (biology)|families]].
 
  
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Classification scheme:
+
Rodents are part of the clades Glires (along with [[lagomorph]]s), Euarchontoglires (along with lagomorphs, [[primate]]s, treeshrews, and colugos), and Boreoeutheria (along with most other placental [[mammal]]s). The order Rodentia is classified below to the level of families.
 +
 
 +
[[Image:Apodemus sylvaticus.JPG|thumb|Wood Mouse]]
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[[Image:Porcupine-BioDome.jpg|thumb|North American porcupine]]
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[[Image:Groundhog-Standing2.jpg|thumb|Groundhog ''(Marmota monax),'' on watch for predators]]
 +
[[Image:Streifenhoernchen.jpg|thumb|Siberian Chipmunk ''(Tamias sibiricus)'']]
 +
'''Classification scheme:'''
  
 
'''ORDER RODENTIA''' (from Latin, ''rodere,'' to gnaw)
 
'''ORDER RODENTIA''' (from Latin, ''rodere,'' to gnaw)
 
*Suborder Sciuromorpha
 
*Suborder Sciuromorpha
 
**Family Aplodontiidae: mountain beaver
 
**Family Aplodontiidae: mountain beaver
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**Family Sciuridae: [[squirrel]]s, including chipmunks, woodchucks, and prairie dogs
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**Family Sciuridae: [[squirrel]]s; including chipmunks, woodchucks, and prairie dogs
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**Family [[Gliridae]] (also Myoxidae, Muscardinidae): [[dormouse|dormice]]
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**Family Gliridae (also Myoxidae, Muscardinidae): dormice
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*Suborder [[Castorimorpha]]
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*Suborder Castorimorpha
 
**Superfamily Castoroidea
 
**Superfamily Castoroidea
−
*** Family [[Castoridae]]: [[beaver]]s
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*** Family Castoridae: [[beaver]]s
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**Superfamily [[Geomyoidea]]
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**Superfamily Geomyoidea
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***Family [[Heteromyidae]]: [[kangaroo rat]]s and [[kangaroo mouse|kangaroo mice]]
+
***Family Heteromyidae: kangaroo rats and kangaroo mice
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***Family [[Geomyidae]]: pocket gophers (true gophers)
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***Family Geomyidae: pocket gophers
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*Suborder [[Myomorpha]]
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*Suborder Myomorpha
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**Superfamily [[Dipodoidea]]
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**Superfamily Dipodoidea
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***Family [[Dipodidae]]: jerboas and jumping mice
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***Family Dipodidae: jerboas and jumping mice
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**Superfamily [[Muroidea]]
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**Superfamily Muroidea
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***Family [[Platacanthomyidae]]: spiny dormice
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***Family Platacanthomyidae: spiny dormice
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***Family [[Spalacidae]]: mole rats, bamboo rats, and [[zokor]]s
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***Family Spalacidae: mole rats, bamboo rats, and zokors
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***Family [[Calomyscidae]]: mouse-like hamsters
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***Family Calomyscidae: mouse-like hamsters
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***Family [[Nesomyidae]]: climbing mice, rock mice, white-tailed rat, Malagasy rats and mice
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***Family Nesomyidae: climbing mice, rock mice, white-tailed rat, Malagasy rats and mice
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***Family [[Cricetidae]]: [[hamster]]s, [[New World rats and mice]], [[vole]]s
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***Family Cricetidae: hamsters, New World rats and mice, voles
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***Family [[Muridae]]: true [[mouse|mice]] and [[rat]]s, [[gerbil]]s, spiny mice, [[crested rat]]
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***Family Muridae: true [[mouse|mice]] and [[rat]]s, gerbils, spiny mice, and the crested rat
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*Suborder [[Anomaluromorpha]]
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*Suborder Anomaluromorpha
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**Family [[Anomaluridae]]: scaly-tailed squirrels
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**Family Anomaluridae: scaly-tailed squirrels
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**Family [[Pedetidae]]: springhares
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**Family Pedetidae: springhares
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*Suborder [[Hystricomorpha]]
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*Suborder Hystricomorpha]
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**Family ''incertae sedis'' [[Diatomyidae]]: Laotian rock rat
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**Family ''incertae sedis'' Diatomyidae: Laotian rock rat
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**Infraorder [[Ctenodactylomorphi]]
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**Infraorder Ctenodactylomorphi
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***Family [[Ctenodactylidae]]: gundis
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***Family Ctenodactylidae: gundis
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**Infraorder [[Hystricognathi]]
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**Infraorder Hystricognathi
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***Family [[Hystricidae]]: Old World porcupines
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***Family Hystricidae: Old World [[porcupine]]s
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***Family [[Erethizontidae]]: New World porcupines
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***Family Erethizontidae: New World porcupines
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***Family [[Thryonomyidae]]: cane rats
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***Family Thryonomyidae: cane rats
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***Family [[Petromuridae]]: dassie rat
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***Family Petromuridae: dassie rat
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***Family [[Bathyergidae]]: African mole rats
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***Family Bathyergidae: African mole rats
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***Parvorder [[Caviomorpha]]
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***Parvorder Caviomorpha
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****Family [[Octodontidae]]: octodonts
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****Family Octodontidae: octodonts
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****Family [[Echimyidae]]: spiny rats
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****Family Echimyidae: spiny rats
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****Family [[Capromyidae]]: hutias
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****Family Capromyidae: hutias
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****Family †[[Heptaxodontidae]]: giant hutias
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****Family †Heptaxodontidae: giant hutias
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****Family [[Myocastoridae]]: nutria
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****Family Myocastoridae: nutria
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****Family [[Dasyproctidae]]: agoutis
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****Family Dasyproctidae: agoutis
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****Family [[Dinomyidae]]: pacaranas
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****Family Dinomyidae: pacaranas
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****Family [[Caviidae]]: cavies, including [[guinea pig]]s
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****Family Caviidae: cavies; including [[guinea pig]]s
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****Family [[Hydrochoeridae]]: Capybara
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****Family Hydrochoeridae: [[capybara]]
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****Family [[Chinchillidae]]: [[chinchilla]]s and viscachas
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****Family Chinchillidae: chinchillas and viscachas
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****Family [[Abrocomidae]]: chinchilla rats
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****Family Abrocomidae: chinchilla rats
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****Family [[Ctenomyidae]]: [[tuco-tuco]]s
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****Family Ctenomyidae: tuco-tucos
  
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===Alternate classifications===
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==References==
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The above [[taxonomy]] uses the shape of the [[mandible|lower jaw]] ([[Sciurognathi|sciurognath]] or [[Hystricognathi|hystricognath]]) as the primary character.  This is the most commonly used approach for dividing the [[Order (biology)|order]] into [[suborders]].  Many older references emphasize the [[zygomasseteric system]] (suborders [[Protrogomorpha]], [[Sciuromorpha]], [[Hystricomorpha]], and [[Myomorpha]]).
 
−
 
 
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Several [[molecular phylogeny|molecular phylogenetic]] studies have used [[gene]] sequences to determine the relationships among rodents, but these studies are yet to produce a single consistent and [[statistical support|well-supported]] [[taxonomy]].  Some [[clade]]s have been consistently produced such as:
 
−
 
 
−
*[[Ctenohystrica]] contains:
 
−
**[[Ctenodactylidae]] (gundis)
 
−
**[[Hystricognathi]] containing:
 
−
***[[Hystricidae]]
 
−
***An unnamed [[clade]] containing:
 
−
****[[Phiomorpha]]
 
−
****[[Caviomorpha]]
 
  
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*An unnnamed [[clade]] contains:
+
* Attenborough, D. ''The Life of Mammals.'' Princeton, New Jersey: Princeton University Press. 2002. ISBN 0691113246
−
**[[Gliridae]]
+
* Invasive Species Specialist Group (ISSG). [http://www.issg.org/database/species/ecology.asp?si=19&fr=1&sts= ''Rattus rattus'' (mammal).] Retrieved September 28, 2007.
−
**[[Sciuroidea]] containing:
+
* IUCN Species Survival Commission (IUCN). [http://www.iucnredlist.org 2007 ICUN Red List of Threatened Species.] Retrieved September 28, 2007.
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***[[Aplodontiidae]]
+
* Nowak, R.M., and Paradiso, J.L. ''Walker's Mammals of the World.'' Baltimore, Maryland: The Johns Hopkins University Press. 1983. ISBN 0801825253
−
***[[Sciuridae]]
+
* University of California Museum of Paleontology (UCMP). [http://www.ucmp.berkeley.edu/mammal/rodentia/rodentia.html Introduction to the Rodentia.] Retrieved September 28, 2007.
−
 
+
* Voelker, W. ''The Natural History of Living Mammals.'' Medford, New Jersey: Plexus Publishing, Inc. 1986. ISBN 0937548081
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*[[Myodonta]] includes:
 
−
**[[Dipodoidea]]
 
−
**[[Muroidea]]
 
−
 
 
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The positions of the [[Castoridae]], [[Geomyoidea]], [[Anomaluridae]], and [[Pedetidae]] are still being debated.
 
−
 
 
−
==References==
 
−
*MacClintock, D. 1970. ''Squirrels of North America''. New York : Van Nostrand Reinhold Company.  
 
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*Nowak, R. M., and J. L. Paradiso. 1983. ''Walker's Mammals of the World''. Baltimore, Maryland: The Johns Hopkins University Press. ISBN 0801825253
 
−
*University of California Museum of Paleontology (UCMP). 2007 "Rodentia". [http://www.ucmp.berkeley.edu/mammal/rodentia/rodentia.html]
 
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*Voelker, W. 1986. ''The Natural History of Living Mammals''. Medford, New Jersey: Plexus Publishing, Inc. ISBN 0937548081
 
  
 
{{Mammals}}
 
{{Mammals}}
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{{Rodents}}
 
  
 
[[Category:Life sciences]]
 
[[Category:Life sciences]]
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[[Category:Animals]]
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[[Category:Mammals]]
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[[Category:Rodents]]
 
{{credit|103654097}}
 
{{credit|103654097}}

Latest revision as of 00:37, 4 April 2008

Rodents
Fossil range: Late Paleocene - Recent
White-tailed Antelope Squirrel, Ammospermophilus leucurus
White-tailed Antelope Squirrel, Ammospermophilus leucurus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Eutheria
(unranked) Euarchontoglires
Superorder: Glires
Order: Rodentia
Bowdich, 1821
Suborders

Sciuromorpha
Castorimorpha
Myomorpha
Anomaluromorpha
Hystricomorpha

Rodents are members of the order Rodentia, which is the largest order of mammals. Rodents are mostly distinguished by their teeth—the word "rodent" comes from the Latin word rodere, meaning "to gnaw."

There are about 1,500 species of rodents including mice, rats, squirrels, and beavers (Nowak, 1983; UCMP, 2007). They are found on all continents except Antarctica and in almost all land habitats, from tropical forests to deserts to mountains to tundras. Rodents and bats are the only orders of placental mammals with species native to Australia.

While some rodents have a reputation as agricultural pests or vectors of disease, rodents in general provide significant ecological, dietary, aesthetic, and scientific values. In many habitats, they are very abundant, and thus are important in food webs and in dispersal of plant seeds. Some species have provided food and fur to human beings, and the trapping of beavers for fur was historically important in North America. Laboratory rats, mice, and guinea pigs have contributed greatly as model organisms in scientific research.

Rabbits, hares, and pikas are not rodents, but members of another order, Lagomorpha.

Rodent Characteristics

Typical rodent tooth system

The incisor teeth of rodents are their most distinctive feature. A rodent's incisors grow continuously throughout its life and must be kept worn down by gnawing. The incisors of a pocket gopher can grow 20 inches in one year. The incisors have enamel on the outside and exposed dentine on the inside, so they self-sharpen during gnawing. Rodents lack canines and first premolars, which creates a space between their incisors and their grinding teeth.

Most rodents are small; the tiny African pygmy mouse (Mus minutoides) is one of the smallest rodents at only 2.5 inches (6 cm) long and weighing only .25 oz (7 grams). The largest living rodent, the capybara (Hydrochoerus hydrochaeris), can weigh up to one hundred pounds (45 kg) and the extinct Phoberomys pattersoni is believed to have weighed up to 1,500 pounds (700 kg).

Most rodents mature quickly and soon produce offspring. A female meadow mouse (Microyus pennsyvanicus) can have up to 17 litters of 4 to 13 young in a year.

Many rodents have an average life span of only a year or less, although some larger rodents such as beavers and porcupines can live over 20 years. The oldest recorded rodent was a Sumatran Crested Porcupine (Hystrix brachyura) that lived 27 years and three months (Voelker, 1986).

Rodents in Nature

Capybara, the largest living rodent

Most rodents eat plants, including seeds, fruit, grasses, and leaves, as well as the bark of trees. Some rodents prey on insects and other small animals. The fish-eating rats (Ichthyomys species) of South America (and some others) swim in streams to catch small fish.

The naked mole rat (Heterocephalus glaber) spends its entire life underground. Flying squirrels live their lives in trees and glide, not truly fly, between trees to avoid spending time on the ground. Many rodents living in colder climates hibernate to conserve energy during the winter.

Some squirrels help maintain and spread forests by burying the seeds of trees. The seeds of the Brazil nut tree will not germinate unless they are first gnawed open and buried by an agouti (Dasyprocta species) (Attenborough, 2002). Gophers, ground hogs, prairie dogs, and other burrowing rodents enrich the soil by mixing it and by burying vegetation. Beavers (Castor species) help control flooding and create pond and meadow habitats with their dam building, which benefits many other species,.

Rodents are often the most abundant small vertebrates in their habitats and are an important source of food for many other animals, including birds, reptiles, and other mammals. If their numbers were not kept in check by predators, rodents would soon over run their environments. Norwegian lemmings (Lemmus lemmus), and some other rodents, undergo "population explosions" every few years. This is thought to help them expand their range into new areas.

Rodents and Humans

From earliest times, rodents have been eaten by humans. Although the flesh of all species is edible, rodents are not an important food source in the world today. Among the exceptions are the capybara and the guinea pig (Cavia porcellus) of South America and the bandicoot rat (Bandicota bengalensis) of Southeast Asia. The dormouse (Glis glis) was considered a delicacy in ancient Rome and is still eaten in parts of Europe today. In North America, squirrels, groundhogs, muskrats, and porcupines are sometimes eaten.

The fur of some rodents is an important product. The trapping of beavers for their fur played an important part in the history of North America. Some other rodents are also trapped for fur in the wild, while the chinchilla (Chinchilla laniger) of South America is raised for its fur.

The greatest impact of rodents on humans began when agriculture started and people chose to live in settled homes. At that time, some rodent species moved into human dwellings, especially to eat stored grain and food scraps and to benefit from warm living spaces and protection from predators. The house mouse (Mus musculus), which seems to be native from the Mediterranean area to China, and several species of rats (Rattus species), native to Southeast Asia, were the most successful and now live with humans all over the world. Although the great majority of rodent species do no harm to humans, these commensal (which means "sharing the same table") species, especially rats, do a tremendous amount of damage to crops and stored food. They also spread diseases, including the bubonic plague, that have killed tens of millions of people through history and are still a danger today.

Laboratory rat in a water maze experiment

Rats also do a lot of damage to the environments that they have been introduced to by humans. The black rat (Rattus rattus), also known as the ship rat, was carried around the world on sailing ships and has contributed to the extinction of many species of birds and other animals, especially on remote islands (ISSG, 2007). Many wild rodent species and subspecies are now endangered because of habitat loss and introduction of invasive species, including rats (IUCN, 2007).

Some species of rodents are kept as pets. One of the most popular rodent pets is the golden hamster (Mesocricetus auratus). All of the world's pet golden hamsters are considered to be descendants of one family captured in Syria in 1930 (Voelker, 1986). Other rodent pets include mice, rats, and guinea pigs.

Rodents also play an important role as subjects of scientific research. One reason for this is that with their short lives many generations can be studied in a few years. Research on mice, rats, and guinea pigs has contributed greatly to our understanding of biological processes and has helped to save millions of human lives.

Classification

Rodents are part of the clades Glires (along with lagomorphs), Euarchontoglires (along with lagomorphs, primates, treeshrews, and colugos), and Boreoeutheria (along with most other placental mammals). The order Rodentia is classified below to the level of families.

Wood Mouse
North American porcupine
Groundhog (Marmota monax), on watch for predators
Siberian Chipmunk (Tamias sibiricus)

Classification scheme:

ORDER RODENTIA (from Latin, rodere, to gnaw)

  • Suborder Sciuromorpha
    • Family Aplodontiidae: mountain beaver
    • Family Sciuridae: squirrels; including chipmunks, woodchucks, and prairie dogs
    • Family Gliridae (also Myoxidae, Muscardinidae): dormice
  • Suborder Castorimorpha
    • Superfamily Castoroidea
    • Superfamily Geomyoidea
      • Family Heteromyidae: kangaroo rats and kangaroo mice
      • Family Geomyidae: pocket gophers
  • Suborder Myomorpha
    • Superfamily Dipodoidea
      • Family Dipodidae: jerboas and jumping mice
    • Superfamily Muroidea
      • Family Platacanthomyidae: spiny dormice
      • Family Spalacidae: mole rats, bamboo rats, and zokors
      • Family Calomyscidae: mouse-like hamsters
      • Family Nesomyidae: climbing mice, rock mice, white-tailed rat, Malagasy rats and mice
      • Family Cricetidae: hamsters, New World rats and mice, voles
      • Family Muridae: true mice and rats, gerbils, spiny mice, and the crested rat
  • Suborder Anomaluromorpha
    • Family Anomaluridae: scaly-tailed squirrels
    • Family Pedetidae: springhares
  • Suborder Hystricomorpha]
    • Family incertae sedis Diatomyidae: Laotian rock rat
    • Infraorder Ctenodactylomorphi
      • Family Ctenodactylidae: gundis
    • Infraorder Hystricognathi
      • Family Hystricidae: Old World porcupines
      • Family Erethizontidae: New World porcupines
      • Family Thryonomyidae: cane rats
      • Family Petromuridae: dassie rat
      • Family Bathyergidae: African mole rats
      • Parvorder Caviomorpha
        • Family Octodontidae: octodonts
        • Family Echimyidae: spiny rats
        • Family Capromyidae: hutias
        • Family †Heptaxodontidae: giant hutias
        • Family Myocastoridae: nutria
        • Family Dasyproctidae: agoutis
        • Family Dinomyidae: pacaranas
        • Family Caviidae: cavies; including guinea pigs
        • Family Hydrochoeridae: capybara
        • Family Chinchillidae: chinchillas and viscachas
        • Family Abrocomidae: chinchilla rats
        • Family Ctenomyidae: tuco-tucos

References
ISBN links support NWE through referral fees

  • Attenborough, D. The Life of Mammals. Princeton, New Jersey: Princeton University Press. 2002. ISBN 0691113246
  • Invasive Species Specialist Group (ISSG). Rattus rattus (mammal). Retrieved September 28, 2007.
  • IUCN Species Survival Commission (IUCN). 2007 ICUN Red List of Threatened Species. Retrieved September 28, 2007.
  • Nowak, R.M., and Paradiso, J.L. Walker's Mammals of the World. Baltimore, Maryland: The Johns Hopkins University Press. 1983. ISBN 0801825253
  • University of California Museum of Paleontology (UCMP). Introduction to the Rodentia. Retrieved September 28, 2007.
  • Voelker, W. The Natural History of Living Mammals. Medford, New Jersey: Plexus Publishing, Inc. 1986. ISBN 0937548081
Mammals
Monotremata (platypus, echidnas)

Marsupialia: | Paucituberculata (shrew opossums) | Didelphimorphia (opossums) | Microbiotheria | Notoryctemorphia (marsupial moles) | Dasyuromorphia (quolls and dunnarts) | Peramelemorphia (bilbies, bandicoots) | Diprotodontia (kangaroos and relatives)

Placentalia: Cingulata (armadillos) | Pilosa (anteaters, sloths) | Afrosoricida (tenrecs, golden moles) | Macroscelidea (elephant shrews) | Tubulidentata (aardvark) | Hyracoidea (hyraxes) | Proboscidea (elephants) | Sirenia (dugongs, manatees) | Soricomorpha (shrews, moles) | Erinaceomorpha (hedgehogs and relatives) Chiroptera (bats) | Pholidota (pangolins)| Carnivora | Perissodactyla (odd-toed ungulates) | Artiodactyla (even-toed ungulates) | Cetacea (whales, dolphins) | Rodentia (rodents) | Lagomorpha (rabbits and relatives) | Scandentia (treeshrews) | Dermoptera (colugos) | Primates |

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