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 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 T ...

Classification

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

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

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

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 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 ...

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 Homoplasy, homoplasies, which are explained as a result ...

appears to be a product of long branch attraction. 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 sou ...

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 w ...

ns, xenarthrans, and meridiungulates 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 ...

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 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 ...

, 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 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 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 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 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'', ...

*** † Chapattimyidae *** 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. "La ...

- 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 A ...

***** 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 ***** Hystricidae - Old World porcupines ***** † Kenyamyidae ***** † Myophiomyidae ***** Petromuridae - dassie rat ***** † Phiomyidae ***** Thryonomyidae - cane rats **** Caviomorpha - New World hystricognaths ***** Superfamily Cavioidea ****** Caviidae - cavies, capybaras, and guinea pigs ****** † Cephalomyidae ****** Cuniculidae - pacas ****** Dasyproctidae - agoutis and acouchis ****** Dinomyidae - pacarana ****** † Eocardiidae ****** † Neoepiblemidae ***** 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 ...

- chinchillas and viscachas ***** Superfamily Erethizontoidea ****** Erethizontidae - New World porcupines ***** Superfamily Octodontoidea ****** 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