By Phil Myers
The single member of this family, the pacarana, is found in the foothills and adjacent slopes of the Andes in northern South America.
These large rodents have a broad head, massive body, and moderately short legs. They weigh around 10-15 kg. The tail is approximately 1/3 the length of the head and body and is densely covered with hair. The head is exceptionally large and broad, with short rounded ears and fairly large eyes. All feet have four digits, each with a heavy and sharp claw, and the posture of these animals is plantigrade. The feet seem to be adapted to digging, but pacaranas are not known as diggers. The vibrissae are unusually long, equalling or exceeding the head in length.
Pacaranas are dark brown in color on their backs, with longitudinal rows of stripes and spots. Underneath is paler. The fur is coarse and scant.
The 
skull of pacaranas is hystricomorphous and strongly hystricognathus, heavily built but only slightly ridged, with heavy zygomatic arches. The infraorbital foramen is large and lacks an accessory canal or groove for the passage of nerves. The jugal does not contact the lacrimal. On the ventral surface of the skull, the auditory bullae are not especially large and the paroccipital processes are short. The coronoid process of the lower jaw is vestigial.
The cheekteeth of a pacarana are highly hypsodont, unrooted, and made up of numerous transverse plates. The incisors are broad and powerful. The dental formula is 1/1, 0/0, 1/1, 3/3 = 20.
These animals are rare, perhaps in danger of extinction. Little is known about their natural history. They are vegetarian, consuming leaves as well as fruit and stems. They appear to move slowly, sit on their haunches when feeding, and apparently are capable of climbing trees. They communicate by stamping their forepaws, chattering their teeth, and emitting a variety of whimpers, whines, hisses, and other vocalizations.
Dinomyids were more diverse in the past, with around 8 fossil genera known. The earliest records are from the Oligocene.
References and literature cited
Feldhamer, G. A., L. C. Drickamer, S. H. Vessey, and J. F. Merritt. 1999. Mammalogy. Adaptation, Diversity, and Ecology. WCB McGraw-Hill, Boston. xii+563pp.
Lawlor, Timothy. 1979. Handbook to the orders and families of living mammals. Mad River Press, Eureka, California.
Macdonald, David. 1984. The encyclopedia of mammals. Facts on File Publications, New York.
Nowak, Ronald M. and John L. Paradiso. 1983. Walker's mammals of the world. The Johns Hopkins University Press, Baltimore and London, pp 803-810.
Vaughan, T. A. 1986. Mammalogy. Third Edition. Saunders College Publishing, Fort Worth. vii+576 pp.
Vaughan, T. A., J. M. Ryan, N. J. Czaplewski. 2000. Mammalogy. Fourth Edition. Saunders College Publishing, Philadelphia. vii+565pp.
Wilson, Don E. and DeeAnn M. Reeder (eds.). 1993. Mammal species of the world: A taxonomic and geographic reference, 2nd ed.. Smithsonian Institution Press, Washington and London.
Woods, C. A. 1984. Hystricognath rodents. Pp. 389-446 in Anderson, Sydney and J. Know Jones, Jr. (eds.). Orders and familes of mammals of the world. John Wiley and Sons, New York.
Contributors
Phil Myers (author), Museum of Zoology, University of Michigan.
