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 a hole below each eye socket (called 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.
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.[1]
^Fagen, Robert. Animal Play Behavior. Oxford University Press, 1981.
Sources
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 ISBN0-231-11012-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 ISBN1-56098-217-9 Corrections were made to text at 3rd printing
