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, Ctenodactylidae, Anomaluridae, and Pedetidae. 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.

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. Considerable morphological and strong

molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...

support exists for this relationship. If true, this hypothesis renders the traditional view of Sciurognathi invalid, as it becomes a

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

group. The hystricomorph rodents, or at least members of Caviomorpha, are sometimes not regarded as rodents. Most molecular and genetic research, however, confirms the monophyly of rodents.; ; ; ; ; Support for rodent

polyphyly 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 converg ...

appears to be a product of long branch attraction. Hystricomorph rodents appeared in South America 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 well ...

ns, xenarthrans, 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 across the Atlantic from Africa. The same type of migration may have occurred with

primates Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...

, which also appeared in South America in the Eocene when it was an isolated continent, long before the

Great American Interchange The Great American Biotic Interchange (commonly abbreviated as GABI), also known as the Great American Interchange and the Great American Faunal Interchange, was an important late Cenozoic paleozoogeographic biotic interchange event in which lan ...

. 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 of and , who subjected a number of early fossil rodents to

parsimony Parsimony refers to the quality of economy or frugality in the use of resources. Parsimony may also refer to * The Law of Parsimony, or Occam's razor, a problem-solving principle ** Maximum parsimony (phylogenetics), an optimality criterion in p ...

analysis and recovered support for the Hystricomorpha or Entodacrya hypothesis. Their results rendered the suborder Sciuravida as defined by to be polyphyletic and invalid. The symbol "†" is used to indicate

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

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 *** Ctenodactylidae - gundis *** Diatomyidae - Laotian rock rat *** † 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 ...

*** Hystricognathi - true hystricognaths **** † Baluchimyinae ****

Phiomorpha The rodent parvorder or infraorder Phiomorpha comprises several living and extinct families found wholly or largely in Africa. Along with Anomaluromorpha and perhaps the extinct Zegdoumyidae, it represents one of the few early colonizations of ...

***** Bathyergidae - blesmols ***** †

Bathyergoididae ''Bathyergoides'' is an extinct genus of rodent from Africa thought to be related to the modern blesmols. It is the only member of the family Bathyergoididae. Fossils of ''Bathyergoides neotertiarius'' were recovered from the Early Miocene Elisab ...

***** †

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 - dassie rat ***** † Phiomyidae ***** Thryonomyidae - cane rats **** Caviomorpha - 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 - cavies, capybaras, and guinea pigs ****** †

Cephalomyidae Cephalomyidae is an extinct family of caviomorph rodents from South America. The specific relationships of the family are uncertain, and affinities to both chinchilloid and cavioid rodents have been supported. Most recently, Kramarz in 2005 per ...

****** Cuniculidae - pacas ****** Dasyproctidae - agoutis and acouchis ****** Dinomyidae - pacarana ****** † Eocardiidae ****** † Neoepiblemidae ***** Superfamily

Chinchilloidea 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 ...

****** 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 The New World porcupines, family Erethizontidae, are large arboreal rodents, distinguished by their spiny coverings from which they take their name. They inhabit forests and wooded regions across North America, and into northern South America. A ...

****** 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 - spiny rats ****** † Heptaxodontidae - giant hutias ****** Myocastoridae - nutria ****** Octodontidae - degus and relatives

Citations

General references

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