Hystricognathi

Hystricognathi Temporal range: Late Eocene–Recent PreЄ Є O S D C P T J K Pg N
Capromys pilorides
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
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

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 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.

The 18 families within the Hystricognathi are 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

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.

Phiomorphan hystricognath families

• Bathyergidae (African mole rats)
• Hystricidae (Old World porcupines)
• Petromuridae (dassie rat)
• Thryonomyidae (cane rats)

Caviomorphan hystricognath families

• 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 (coypu)
• Octodontidae (13 species including the degu)

References

• 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
• Charles A. Woods Florida Museum of Natural History, University of Florida, Gainesville, FL 32611-2035
• 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 0-231-11012-X
• 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 1-56098-217-9 Corrections were made to text at 3rd printing

External links

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

See also

• Sciurognathi
• Hystricomorpha