The Hystricognathi are an

infraorder Order ( la, ordo) 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 ...

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

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 is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

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 anatomica ...

) 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 la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...

within the Hystricognathi are divided into two

parvorder Order ( la, ordo) 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 ...

s, the Phiomorpha and the

Caviomorpha Caviomorpha is the rodent infraorder or 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 ...

. 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 relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

, with a few species in the Caribbean and North America, while the Phiomorpha occur in the Old World.

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 "unispe ...

taxon) * Hystricidae (Old World porcupines) *

Petromuridae Petromuridae is a family of hystricognath rodents that contains the dassie rat ''(Petromus typicus)'' of southwestern Africa, the only extant member of this group. The genus ''Petromus ''Petromus'' is a genus of hystricognath rodents that co ...

(dassie rat,

taxon) *

Thryonomyidae Thryonomyidae is a family of hystricognath rodents that contains the cane rats ''(Thryomys)'' found throughout sub-Saharan Africa, and a number of fossil genera. Taxonomy Thryonomyidae was formerly more diverse and widespread, with fossil relati ...

(cane rats)

Caviomorphan hystricognath families

* Abrocomidae (chinchilla rats) * Capromyidae (hutias) *

Caviidae Caviidae, the cavy family, is composed of rodents native to South America and includes the domestic guinea pig, wild cavies, and the largest living rodent, the capybara. They are found across South America in open areas from moist savanna to tho ...

(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 but ...

(chinchillas and viscachas) *

Ctenomyidae A tuco-tuco is a neotropical rodent in the family Ctenomyidae.Parada, A., G. D’Elia, C.J. Bidau, and E.P. Lessa. 2011. Species Groups and the Evolutionary Diversification of Tuco-Tucos, genus ''Ctenomys'' (Rodentia: Ctenomyidae). ''Journal of M ...

(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 herbivorous, often feeding on ripe fruit that falls from trees. They liv ...

(agoutis and acouchis) *

Dinomyidae The Dinomyidae are a 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 largest rodents know ...

(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 ''Proechimys'' is a genus of South American spiny rats of the family Echimyida ...

(coypu) *

Octodontidae Octodontidae is a family of rodents, restricted to southwestern South America. Fourteen species of octodontid are recognised, arranged in seven genera. The best known species is the common degu, ''Octodon degus''. Octodontids are medium-sized ...

(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 Rodent taxonomy Mammal infraorders Extant Eocene first appearances