Hystricomorpha (from Greek ὕστριξ, hystrix 'porcupine' and Greek μορφή, morphē 'form')[2] 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 Carleton & Musser 2005, these two families are discussed here as representing a distinct suborder Anomaluromorpha.
The modern definition of Hystricomorpha, also known as EntodacryaorCtenohystrica, is a taxonomic hypothesis uniting the gundis with the hystricognath rodents.[3] 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.[4] Most molecular and genetic research, however, confirms the monophyly of rodents.[5] Support for rodent polyphyly appears to be a product of long branch attraction.[6]
Hystricomorph rodents appeared in South America in the Eocene,[7] a continent which previously had metatherians, xenarthrans, and meridiungulates as the only resident nonflying mammals[citation needed]. They apparently arrived by rafting across the Atlantic from Africa. The same type of migration may have occurred with primates,[8] 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.
^Bond, M.; Tejedor, M. F.; Campbell, K. E.; Chornogubsky, L.; Novo, N.; Goin, F. (2015-02-04). "Eocene primates of South America and the African origins of New World monkeys". Nature. 520 (7548): 538–41. doi:10.1038/nature14120. hdl:11336/79088. PMID25652825. S2CID4456556.
Carleton, M. D.; Musser, G. G. (2005). "Order Rodentia". In Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World A Taxonomic and Geographic Reference. Baltimore: Johns Hopkins University Press. pp. 745–752. ISBN978-0-8018-8221-0.
D'Erchia, A.; Gissi, C.; Pesole, G.; Saccone, C.; Arnason, U. (1996). "The guinea-pig is not a rodent". Nature. 381 (6583): 597–600. doi:10.1038/381597a0. PMID8637593. S2CID4336262.
Marivaux, L.; Welcomme, J.-L.; Vianey-Liaud, M.; Jaeger, J.-J. (2002). "The role of Asia in the origin and diversification of hystricognathous rodents". Zoologica Scripta. 31 (3): 225–239. doi:10.1046/j.1463-6409.2002.00074.x. S2CID86358222.
McKenna, M. C.; Bell, S. K. (1997). Classification of Mammals Above the Species Level. New York: Columbia University Press. ISBN0-231-11013-8.
Reyes, A.; Pesole, G.; Saccone, C. (2000). "Long-branch attraction phenomenon and the impact of among-site rate variation on rodent phylogeny". Gene. 259 (1–2): 177–187. doi:10.1016/S0378-1119(00)00438-8. PMID11163975.
