The Hystricognathi are an

infraorder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between Family_(biology), family and Class_(biology), class. In biological classification, the order is a taxonomic rank used in the classific ...

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

s, distinguished from other rodents by the

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

structure of their

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

s. The masseter medialis (a jaw muscle) passes partially through a hole below each eye socket (called the

infraorbital foramen In human anatomy, the infraorbital foramen is one of two small holes in the skull's upper jawbone ( maxillary bone), located below the eye socket and to the left and right of the nose. Both holes are used for blood vessels and nerves. In anatomic ...

) and connects to the bone on the opposite side. This, together with their lack of an infraorbital plate and the relative size of the

, distinguishes hystricognaths from other rodent groups. The 18

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

within the Hystricognathi are divided into two

parvorder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...

s, the Phiomorpha and the

Caviomorpha Caviomorpha is the rodent parvorder that unites all New World hystricognaths. It is supported by both fossil and molecular evidence. The Caviomorpha was for a time considered to be a separate order outside the Rodentia, but is now accepted as ...

. The Caviomorpha are mostly native to

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

, with a few species in the

Caribbean The Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean, mostly overlapping with the West Indies. Bordered by North America to the north, Central America ...

and

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

, while the Phiomorpha occur in the

Old World The "Old World" () is a term for Afro-Eurasia coined by Europeans after 1493, when they became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia in the Eastern Hemisphere, previously ...

Behavior

Play behavior has been observed in seven hystricognath families. The caviomorphs chase each other, play-wrestle, and gallop. The longer-legged species chase more often than the shorter-legged species. They also rotate their heads and body muscles as a form of play.Fagen, Robert. ''Animal Play Behavior''. Oxford University Press, 1981.

Phiomorphan hystricognath families

* Bathyergidae (African mole rats) * Heterocephalidae (naked mole rats,

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

taxon) * Hystricidae (Old World porcupines) * Petromuridae (dassie rat,

taxon) * Thryonomyidae (cane rats)

Caviomorphan hystricognath families

* Abrocomidae (chinchilla rats) * Capromyidae (hutias) * Caviidae (guinea pigs, wild cavies, and capybaras) *

Chinchillidae The family Chinchillidae is in the order Rodentia and consists of the chinchillas, the viscachas, and their fossil relatives. This family is restricted to southern and western South America, mostly living in mountainous regions of the Andes, ex ...

(chinchillas and viscachas) *

Ctenomyidae A tuco-tuco is a neotropical rodent in the family Ctenomyidae. Tuco-tucos belong to the only living genus of the family Ctenomyidae, ''Ctenomys'', but they include approximately 60 different species. The common name, "tuco-tuco", comes from the " ...

(tuco-tucos) * Cuniculidae (pacas) *

Dasyproctidae Dasyproctidae is a family of large South American rodents, comprising the agoutis and acouchis. Their fur is a reddish or dark colour above, with a paler underside. They are herbivore, herbivorous, often feeding on ripe fruit that falls from tree ...

(agoutis and acouchis) *

Dinomyidae The Dinomyidae are a family (biology), family of South American hystricognath rodents: the dinomyids were once a very speciose group, but now contains only a single living species, the pacarana. Several of the extinct dinomyids were among the la ...

(pacaranas and their fossil relatives, including some of megafaunal size) *

Echimyidae Echimyidae is the family of neotropical spiny rats and their fossil relatives. This is the most species-rich family of hystricognath rodents. It is probably also the most ecologically diverse, with members ranging from fully arboreal to terr ...

(spiny rats) * Erethizontidae (New World porcupines) *

Myocastoridae Myocastorini is a tribe of echimyid rodents, proposed in 2017, and containing the five extant genera ''Callistomys'', ''Hoplomys'', ''Myocastor'', ''Proechimys'', and ''Thrichomys''. Definition Myocastorini members share long upper incisor ro ...

(coypu) * Octodontidae (13 species including the degus)

References

Citations

Sources

* Alfred L. Gardner Curator of North American mammals and Chief of Mammal Section, National Biological Service, Smithsonian Institution, National Museum of Natural History, Washington, DC, USA * Charles A. Woods Florida Museum of Natural History, University of Florida, Gainesville, FL 32611-2035 * McKenna, Malcolm C. and Susan K. Bell 1997 ''Classification of mammals above the species level'' 631 Columbia University Press New York, New York, USA * Wilson, Don E., and DeeAnn M. Reeder, eds. 1993 ''Mammal Species of the World: A Taxonomic and Geographic Reference'', 2nd ed., 3rd printing xviii + 1207 Smithsonian Institution Press Washington, DC, USA Corrections were made to text at 3rd printing

External links

* https://web.archive.org/web/20061130080256/http://animaldiversity.ummz.umich.edu/site/topics/mammal_anatomy/rodent_jaws.html {{Taxonbar, from=Q1063601 Hystricomorpha Rodent taxonomy Mammal infraorders Extant Eocene first appearances