The term Hystricomorpha (from Greek ὕστριξ, ''hystrix'' 'porcupine' and Greek μορφή, ''morphē'' 'form') has had many definitions throughout its history. In the broadest sense, it refers to any rodent (except dipodoids) with a hystricomorphous zygomasseteric system. This includes the

Hystricognathi The Hystricognathi are an infraorder of rodents, distinguished from other rodents by the bone 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, fa ...

, Ctenodactylidae, Anomaluridae, and

Pedetidae The Pedetidae are a family of mammals from the rodent order. The two living species, the springhares, are distributed throughout much of southern Africa and also around Kenya, Tanzania, and Uganda. Fossils have been found as far north as Turkey.M ...

. Molecular and morphological results suggest the inclusion of the Anomaluridae and Pedetidae in Hystricomorpha may be suspect. Based on , these two families are discussed here as representing a distinct suborder

Anomaluromorpha Anomaluromorpha is a clade that unites the anomalures, springhares, and zenkerella. It has alternately been designated as either a suborder or infraorder. Most recently, recognized it as one of five suborders of rodents. Characteristics ...

Classification

The modern definition of Hystricomorpha, also known as Entodacrya or Ctenohystrica, is a taxonomic hypothesis uniting the

gundi Gundis or comb rats (family Ctenodactylidae) are a group of small, stocky rodents found in Africa. They live in rocky deserts across the northern parts of the continent. The family comprises four living genera and five species ( Speke's gundi, ...

s with the

hystricognath rodents The Hystricognathi are an infraorder of rodents, distinguished from other rodents by the bone structure of their skulls. The masseter medialis (a jaw muscle) passes partially through a hole below each eye socket (called the infraorbital foramen ...

. Considerable morphological and strong molecular support exists for this relationship. If true, this hypothesis renders the traditional view of

Sciurognathi Sciurognathi is a suborder of rodents that includes squirrels, chipmunks, beavers, and many types of mice. The group is characterized by a specific shape to the lower jaw. In sciurognaths, the angular process of the jaw is in the same plane as ...

invalid, as it becomes a paraphyletic group. The hystricomorph rodents, or at least members of

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 ...

, are sometimes not regarded as rodents. Most molecular and genetic research, however, confirms the

monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

of rodents.; ; ; ; ; Support for rodent polyphyly appears to be a product of

long branch attraction In phylogenetics, long branch attraction (LBA) is a form of systematic error whereby distantly related lineages are incorrectly inferred to be closely related. LBA arises when the amount of molecular or morphological change accumulated within a lin ...

. Hystricomorph rodents appeared in

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 ...

in the Eocene, a continent which previously had

metatheria Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as wel ...

ns,

xenarthra Xenarthra (; from Ancient Greek ξένος, xénos, "foreign, alien" + ἄρθρον, árthron, "joint") is a major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. ...

ns, and

meridiungulates South American native ungulates, commonly abbreviated as SANUs, are extinct ungulate-like mammals of controversial affinities that were indigenous to South America prior to the Great American Biotic Interchange. They comprise five major groups c ...

as the only resident nonflying mammals. They apparently arrived by

rafting Rafting and whitewater rafting are recreational outdoor activities which use an inflatable raft to navigate a river or other body of water. This is often done on whitewater or different degrees of rough water. Dealing with risk is often a ...

across the

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...

from

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

. The same type of migration may have occurred with primates, which also appeared in South America in the Eocene when it was an isolated continent, long before the Great American Interchange. All of this is still controversial, and new scientific discoveries on this subject are published regularly.

Families

The following list of families is based on the

taxonomy Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

of and , who subjected a number of early fossil rodents to parsimony analysis and recovered support for the Hystricomorpha or Entodacrya hypothesis. Their results rendered the suborder Sciuravida as defined by to be

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

and invalid. The symbol "†" is used to indicate extinct groups. * Suborder Hystricomorpha ** Superfamily

Ctenodactyloidea Ctenodactylomorphi is an infraorder of the rodent suborder Hystricomorpha that includes two living families, the Ctenodactylidae (gundis) and the Diatomyidae (Laotian rock rat The Laotian rock rat or ''kha-nyou'' (''Laonastes aenigmamus'', L ...

*** †

Chapattimyidae Chapattimyidae is an extinct family of rodent from Asia. According to Fossilworks, it contains two subfamilies and six unplaced genera. * Subfamily Baluchimyinae Flynn et al. 1986 ** ''Asterattus'' Flynn and Cheema 1994 ** ''Baluchimys'' Flynn ...

*** Ctenodactylidae - gundis ***

Diatomyidae Diatomyidae is a family of hystricomorph rodents. It is represented by a single living species, ''Laonastes aenigmamus,'' native to Laos in Southeast Asia. Fossil species are known from the Oligocene and Miocene of Asia and eastern Europe. "Laz ...

Laotian rock rat The Laotian rock rat or ''kha-nyou'' (''Laonastes aenigmamus'', Lao: ຂະຍຸ), sometimes called the "rat-squirrel", is a species of rodent found in the Khammouan region of Laos. The species was first described in a 2005 article by Paulina ...

*** † Tamquammyidae *** † Yuomyidae ** Hystricognathiformes *** †

Tsaganomyidae The Tsaganomyidae are an extinct family of rodents from Asia. It contains three genera. Tsaganomyids are generally considered to be related to the Hystricognathi (porcupines and relatives). Members of Tsaganomyidae were fossorial (digging) roden ...

***

- true hystricognaths **** † Baluchimyinae **** Phiomorpha ***** Bathyergidae - blesmols ***** † Bathyergoididae ***** †

Diamantomyidae Diamantomyidae is a family of extinct hystricognath rodents from Africa and Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, ...

***** Hystricidae - Old World porcupines ***** †

Kenyamyidae Kenyamyidae is an extinct family of rodents from Africa that lived in the Lower Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages. The ...

***** †

Myophiomyidae Myophiomyidae is an extinct family of Old World hystricognath The Hystricognathi are an infraorder of rodents, distinguished from other rodents by the bone structure of their skulls. The masseter medialis (a jaw muscle) passes partially th ...

*****

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 ***** †

Phiomyidae The Phiomyidae are a family of prehistoric rodents from Africa and Eurasia. A 2011 study placed ''Gaudeamus'' in a new family, Gaudeamuridae. Genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of livin ...

*****

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 ****

- New World hystricognaths ***** Superfamily

Cavioidea Caviomorpha is the rodent infraorder or parvorder that unites all New World hystricognaths. It is supported by both fossil and molecular phylogeny, molecular evidence. The Caviomorpha was for a time considered to be a separate order outside the R ...

******

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 ...

- cavies, capybaras, and guinea pigs ****** † Cephalomyidae ****** 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 ...

- pacarana ****** †

Eocardiidae The Eocardiidae are an extinct family of caviomorph rodents from South America. The family is probably ancestral to the living family Caviidae, which includes cavies, maras, and capybaras and their relatives. McKenna and Bell (1997) divided eoca ...

****** †

Neoepiblemidae The Neoepiblemidae are an extinct family of hystricognath rodents from South America. The genera '' Dabbenea'' and '' Perumys'' are now included in ''Phoberomys''. The delineation between Neoepiblemidae and Dinomyidae has historically been unclea ...

***** Superfamily Chinchilloidea ****** Abrocomidae - chinchilla rats ******

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 ***** Superfamily Erethizontoidea ****** Erethizontidae - New World porcupines ***** Superfamily

Octodontoidea 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 ...

****** Capromyidae - hutias ******

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 ******

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 ****** †

Heptaxodontidae Heptaxodontidae, rarely called giant hutia, is an extinct family (taxonomy), family of large rodents known from fossil and subfossil material found in the West Indies. One species, ''Blunt-toothed giant hutia, Amblyrhiza inundata'', is estimated ...

- giant hutias ******

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 ...

- nutria ******

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 ...

- degus and relatives

Citations

General references

* * * * * * * * * * * * * * * * {{Taxonbar, from=Q532250 Extant Eocene first appearances Mammal suborders Rodent taxonomy th:เม่น