Hystricognaths Fossil range: Late Eocene - Recent
Capromys pilorides
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Suborder:	Hystricomorpha
Infraorder:	Hystricognathi Tullberg, 1899
Families
Hystricidae †Bathyergoididae Bathyergidae †Myophiomyidae †Diamantomyidae †Phiomyidae †Kenyamyidae Petromuridae Thryonomyidae Erethizontidae Chinchillidae †Neoepiblemidae Dinomyidae †Cephalomyidae †Eocardiidae Caviidae Dasyproctidae Cuniculidae Ctenomyidae Octodontidae Abrocomidae Echimyidae Myocastoridae Capromyidae †Heptaxodontidae

Hystricognathi is an infraorder of rodents. Hystricognaths are distinguished from other rodents by the bone structure of their skulls. The masseter medialis (a jaw muscle) passes partially through the infraorbital foramen and connects to the bone on the opposite side. This, together with their lack of an infraorbital plate and the relative size of the infraorbital foramen, distinguishes hystricognaths from other rodent groups.

There are 18 families within the Hystricognathi, divided into two infraorders, the Phiomorpha and the Caviomorpha. The Caviomorpha are mostly native to South America, with a few species in North America, while the Phiomorpha occur in the Old World.

Skull of a Nutria demonstrating the hystricognathous lower jaw and hystricomorphous zygomasseteric system

[edit] Behavior

Play behavior has been observed in seven hystricognath families. The caviomorphs chase each other, play-wrestle, and gallop. The longer-legged species chase more often than the shorter-legged species. They also rotate their heads and body muscles as a form of play (Fagen 1981).

[edit] Phiomorphan hystricognath familiæ

• Bathyergidae
• Hystricidae
• Petromuridae
• Thryonomyidae

[edit] Caviomorphan hystricognath familiæ

• Abrocomidae (chinchilla rats)
• Capromyidae (hutias)
• Caviidae (guinea pigs, wild cavies, and capybaras)
• Chinchillidae (chinchillas, viscachas, and their fossil relatives)
• Ctenomyidae (tuco-tucos)
• Dasyproctidae (agoutis and acouchis)
• Dinomyidae (pacaranas and their fossil relatives)
• Echimyidae (spiny rats)
• Erethizontidae (new world porcupines)
• Myocastoridae (coypus)
• Octodontidae (13 species including the degu)

[edit] References

• Fagen, Robert. Animal Play Behavior. Oxford University Press, 1981.
• Alfred L. Gardner Curator of North American mammals and Chief of Mammal Section, National Biological Service,Smithsonian Institution, National Museum of Natural History, Washington, DC, USA Hystricognathi
• Charles A. Woods Florida Museum of Natural History, University of Florida, Gainesville, FL 32611-2035 Hystricognathi
• McKenna, Malcolm C., and Susan K. Bell 1997 Classification of mammals above the species level 631 Columbia University Press New York, New York, USA ISBN/ISSN 0-231-11012-X Hystricognathi
• Wilson, Don E., and DeeAnn M. Reeder, eds. 1993 Mammal Species of the World: A Taxonomic and Geographic Reference, 2nd ed., 3rd printing xviii + 1207 Smithsonian Institution Press Washington, DC, USA ISBN/ISSN 1-56098-217-9 Corrections were made to text at 3rd printing Hystricognathi

[edit] External links

• http://animaldiversity.ummz.umich.edu/site/topics/mammal_anatomy/rodent_jaws.html

[edit] See also

• Sciurognathi
• Hystricomorpha