Hystricomorpha (from Ancient Greek , (hústrix), meaning "porcupine", and (morphḗ), meaning "form") is a term referring to families and orders of rodents which 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 gundis with the hystricognath rodents. Considerable morphological and strong molecular support exists for this relationship. If true, this hypothesis renders the traditional view of Sciurognathi invalid, as it becomes a paraphyletic 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 appears to be a product of long branch attraction.
Hystricomorph rodents appeared in South America in the Eocene, a continent which previously had metatherians, xenarthrans, and meridiungulates 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, 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 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 and invalid. The symbol "†" is used to indicate extinct groups.
Suborder Hystricomorpha †Pseudoneoreomys? Superfamily Ctenodactyloidea †Chapattimyidae Ctenodactylidae – gundis Diatomyidae – Laotian rock rat †Tamquammyidae †Yuomyidae Hystricognathiformes †Tsaganomyidae Hystricognathi – true hystricognaths †Baluchimyinae Hystricidae – Old World porcupines Phiomorpha Bathyergidae – blesmols †Bathyergoididae †Diamantomyidae Heterocephalidae – naked mole-rats †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 †Eocardiidae †Neoepiblemidae Superfamily Chinchilloidea Chinchillidae – chinchillas and viscachas Dinomyidae – pacarana Superfamily Erethizontoidea Erethizontidae – New World porcupines Superfamily Octodontoidea Abrocomidae – chinchilla rats Ctenomyidae – tuco-tucos Echimyidae – spiny rats, nutria and hutias †Heptaxodontidae – giant hutias Octodontidae – degus and relatives
Citations
General references