Last updated 17 December 2000: added Bathyergidae, Ctenodactylidae and Hystricidae.
The suborder CAVIOMORPHA is centred on South America, with a few representatives in Africa and southern Asia. It is the most diverse of the rodent suborders and contains some of the largest species. Alderton notes that some of the large South American species fill ecological niches that in Africa would be filled by small antelopes. Caviomorphs are distinguished by the arrangement of the masseter muscle, whose deep branch in these rodents is used in the gnawing action of the jaws rather than to close them, and whose point of insertion is on the snout. Caviomorphs also produce fewer young which are in a more advanced and independent stage of development than other rodents when they are born.
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| Abrocomidae, Chinchilla Rats | Agoutidae, Pacas | Bathyergidae, African Mole Rats |
| Capromyidae, Hutias | Cavidae, Cavies | Chinchillidae, Chinchillas and Viscachas |
| Ctenodactylidae, Gundis | Ctenomyidae, Tucos-tucos, Comb Rats | Dasyproctidae, Agoutis and Acouchis |
| Dinomyidae, Pacarana | Echimyidae, Spiny Rats | Erithizontidae, New World Porcupines |
| Hydrochaeridae, Capybara | Hystricidae, Old World Porcupines | Myocastoridae, Coypu |
| Octodontidae, Degus | Petromyidae, African Rock Rat, Dassie Rat | Thryonomyidae, Cane Rats |
| Common Name | Family Name | Origin | Comments |
| Chinchilla Rats | Abrocomidae | S. America (Andes) | This family comprises just two species in a limited range of South America. They can be found at altitudes of over 9,800 ft in the Andes (Alderton). Their dense fur protects them against the cold but is also the main reason for their hunting by man. These herbivorous rodents possess enormously long digestive tracts up to 8ft long and a correspondingly large caecum, although they themselves are only about 10" long. Interestingly the Chilean Chinchilla Rat, A. benetti, possesses more ribs than any other rodent (17 pairs). Chinchilla rats live in burrows which they may share with the degus (Octodon species). Breeding takes place throughout the year but as with many caviomorphs gestation is extremely long, about 118 days. Two young are born. The common name of these creatures derives from their resemblance to chinchillas in all but their rat-like tails. |
| Pacas | Agoutidae | S. America east of the Andes | A family of two species, Cuniculus paca and C. taczanwskii. These are large (up to 33" long) but shy nocturnal rodents that dwell in riverside burrows or caves in forested areas. Although they do occasionally damage crops while foraging for food, they are mainly hunted for their highly-regarded flesh. |
| African Mole Rats | Bathyergidae | Sub-Saharan Africa | Not to be confused with the Blind Mole Rats of the Spalacinae subfamily of the Muridae (see Myomorpha: Mouse-like rodents. The five genera in this family are all burrowers and show the corresponding modifications to their anatomy: reduced eye and ear sizes, short but powerful limbs and usually longer front claws than rear. The dune mole rats (Bathyergus spp.) use their forefeet for digging, but the other species use their incisors. All are tunnelers and feed underground on tubers and similar vegetation, rarely venturing above ground. The silver mole rat Heliophobius argenteocinereus is solitary, but the others are presumably colonial in nature. Apart from the impact they have on agriculture, their tunneling activities can also cause problems for railways that cross their burrows (Alderton). |
| Hutias | Capromyidae | Jamaica, Cuba, Puerto Rico, Hispaniola and Bahamas | An interesting but threatened family of animals whose numbers have been greatly reduced by introduced animals and native hunting, including a few species wiped out. The hutias are relatively long-lived for rodents (about five years) but have a correspondingly long gestation period (110 days) which places them at a corresponding disadvantage. They are good climbers and somewhat arboreal, but many prefer to live in hollows, although they do not dig these themselves. Alderton notes that Capromys species have a three-chambered stomach somewhat similar to that of a ruminant rather than that of a typical rodent. |
| Cavies | Cavidae | Most of South America except north, north-west and Amazon basin. | Includes the guinea pig, Cavia porcellus, mountain- and rock cavies, and the two large species of Patagonian cavy or mara, Dolichotis spp.. |
| Chinchillas and Viscachas | Chinchillidae | Southern S. America inc. Andes) | This family comprises both the Chinchilla and Lagostomus species, all of which were heavily hunted in recent history, plus the Lagidium species. In a reversal of fate, the chinchilla, which was once on the point of extinction, is now one of the favourite domestic pets in the West and is being bred in captivity. The reason for this hunting was the soft fur of these animals which serves to keep them warm at high altitudes (9-13,000 ft). The chinchillas live among crevices in the rocks and are have the defensive adaptation of large ears and eyes which warn them of possible danger over long distances. Breeding season is May to November: gestation is about 113 days, with two young being born. The plains viscacha, Lagostomus maximusis now only found in Argentina and is the largest member of the family, weighing as much as 18lb. These rodents are colonial and live in groups of up to 50 in viscacheras, burrows that may be occupied for centuries and cover over 700 square yards (Alderton). This grouping together tends to mean travelling longer distances to find vegetation, with a subsequent increased danger of predation, but these viscachas are incredibly fast and agile, running at up to 25 mph and twisting and turning if pursued. Unlike the chinchillas, where the female is more aggressive, the male viscachas are the fighters and often fight at the beginning of the breeding season. The mountain viscacha, genus Lagidium, are different in appearance and habitat from the plains viscachas: they have long ears (presumably for the same reason as the chinchilla) and live in higher, rocky areas where they live among the crevices: they do, however, form large colonies like their lowland brethren. |
| Gundis | Ctenodactylidae | N & E Africa | This family contains the Ctenodactylus genus of two species and three other monotypic (single-species) genera. The family name means "comb-fingered" and is based on the bristles above the claws and the two inner toes of the hind foot. Alderton notes that doubt has been raised over the assignment of this family to the Caviomorpha, since the jaw structure is more akin to that of the Sciuromorpha although the jaw musclature is more akin to that of the caviomorphs. In appearance the individual species vary between squirrels (as in Speke's pectinator, Pectinator spekei and guinea pigs with tails (the gundis themselves, Ctenodactylus spp.). The gundis share certain characteristics with the African rock rat, Petromus typicus: they live among rocks and have a flexible rib cage to allow them to squeeze into crevices. They are very colonial and communicate with one another via cheeping and similar calling noises: the young often call the mother back to them from the cover of crevices. Like some desert lizards these rodents absorb all the moisture they need from their food, thus obviating the need to drink. |
| Tuco-tucos, comb rats | Ctenomyidae | Southern S. America inc. Andes but not Patagonia | The Ctenomyidae comprise one genus, Ctenomys, of over 30 species.They are extensive burrowers, living a network of tunnels up to 2ft below the surface. They spend most of their time here, feeding on roots and other plant matter accessible from below, and rarely leave the burrows. They also have a system of maintaining a constant temperature of about 68-70 deg F, which is done by opening or closing various exits. These are hard to locate from outside, and in addition if the creatures feel threatened they rapidly block up the entry tunnels with soil. Their form is adapted for this fossorial existence, with prominent incisors and sharp claws on all toes. The feet have hairs on them to help remove dirt from the coat, while the tail is short but may have a sensory function to aid them, particularly when moving backwards (Alderton). As with many rodents, tuco-tucos are often considered pests, both for the agricultural damage they cause and also the danger to horses represented by the tunnels, which may collapse beneath the weight of one and cause a damaging fall. |
| Agoutis and Acouchis | Dasyproctidae | C. America; N & C S. America | A family of diurnal rodents, smaller than the pacas but possibly closely related. Their large hind legs allow them to jump up over 6ft in the air and also to run fast if necessary, although they prefer to freeze and remain concealed if startled. Their natural habitat is woodland and their diet fruitivorous. A pair of agoutis will usually maintain a certain territory. Males spray the female with urine prior to mating: two twins are usually born after a 16 week gestation. Agoutis and acouchis have long been food items for humans and for this reason some were introduced into the Carribean before the arrival of the Europeans, although most of these are now extinct. |
| Pacarana | Dinomyidae | Highlands of northern S. America | A single-species family, consisting soley of the pacarana, Dinomys branickii. This is a stocky, completely vegetarian rodent with strong claws used for digging or climbing. It is comparatively rare and now threatened by deforestation. |
| Spiny rats | Echimyidae | C America and northern S. America as far as Brazil and Paraguay | This is the largest Caviomorph family with 56 species that show some diversity in form and behaviour. Despite the name, not all have spines, but this trait in the group is well evidenced by such species as the Thick-Spined Rat Hoplomys gymnurus, whose spines may be up to 1" long and which can shed them if seized. Below the spines are normal soft hairs. The actual spiny rats themselves form the genus Proechimys, which have smaller spines than H. gymnurus, and which can also shed their tails at the fifth caudal vertebra: unlike lizards, however, they cannot regenerate the tail once lost. They live in burrows from where they normally emerge at night to forage. They can climb but seem to prefer terrestrial places, and unlike many other rodents they do not seek human civilisation. On the other hand the arboreal spiny rats, Echimys, live in trees and move around branches rather like squirrels (Alderton). However, the majority of this family seem to be fossorial. |
| New World Porcupines | Erithizontidae | N. & S. America | The members of this family are also known as tree porcupines, since they are more arboreal than Old World porcupines and have feet adapted for climbing trees. In addition the Coendou prehensile-tailed porcupines also use their tails to assist in climbing. |
| Capybara | Hydrochaeridae | S. America east of the Andes | The sole species in this family is the world's largest rodent, the capybara, Hydrochaeris hydrochaeris. Heavily hunted for food, they are now fortunately being ranched in some areas (Alderton). They live near water which they use as an escape route if threatened: mating also takes place in the water. |
| Old World Porcupines | Hystricidae | SE Asia, S Europe and Africa | Fairly widespread family, differing from New World porcupines (Erithizontidae) not only in distribution but also in being primarily terrestrial creatures that live in burrows. One member, however, the Long-Tailed Porcupine of Malaysia (Trichys fasciculata), is arboreal: interestingly this one is considered the most primitive genus. The other two genera are the Brush-Tailed Porcupines (Antherurus spp.) and the African crested porcupine and its Asiatic congenerics, Hystrix spp. The quills vary in length from short in the Trichys species to up to 14" in the African Crested Porcupine Hystrix cristata. In this species, the quills are concentrated on the rear and hindquarters and therefore a defensive porcupine will actually back into an attacker. Diet of these porcupines is mainly herbivorous but can include invertebrates, at least with H. cristata (Alderton). Alderton believes those porcupines in southern Europe were probably introduced and notes that they do not hibernate even in this relatively cool part of their range. The main enemies of the porcupine are large cats, mainly lions, and humans who also kill them for their meat. They are the longest-lived of rodents with a natural lifespan of at least 15 years. |
| Coypu | Myocastoridae | S. South America | Consists of single species, the coypu Myocastor coypus. It is an inhabitant of marshy areas and feeds on aquatic vegetation. Coypus were once heavily farmed in countries outside their natural habitat, which caused some ecological damage when escapees established feral populations. |
| Degus | Octodontidae | Southern S. America inc. Andes) | The Octodontidae derive their name from the grinding surfaces on their molars, which are shaped rather like a figure eight. They live in the arid parts of the Andes up to a height of nearly 10,000 ft. The degu (Octodon spp.) is about the same size as a rat but with longer forelimbs than hind limbs. It is a diurnal creature living in burrows which it digs itself, but it is also a good climber. In addition it has the ability to lose part of its tail, rather like a lizard: if restrained by the tail, particularly the tip, it can bite through it to sever the held portion and escape. As with lizards that practise this autotomy, blood loss is minimal and healing is quite quick. Degus may be considered pests in some areas where they damage agriculture through storing up food for the winter, but as with so many rodents they are now also being kept as pets in the more affluent parts of the world. Other members of this family include the cururo, Spalacopus cyanus, which is an active burrower that although diurnal spends much time underground, the viscacha rats, Octomys spp., and the chozchoz, Octodontomys gliroides. These all live within roughly the same range as the degu. |
| African rock rat, dassie rat | Petromyidae | SW Africa | The Petromyidae are a single-species family consisting of the African Rock Rat Petromus typicus. This species is well adapted for living among rocks, having cryptic camouflage and a flexible rib cage to allow it to squeeze into tight gaps. It can also lose its tail, and females have the interesting adaptation of mammary glands that are high up on their body to allow young to suckle from the safety of a crevice (Alderton). |
| Cane rats | Thryonomyidae | Sub-Saharan Africa | The Thryonomyidae comprise just two species, the great cane rat Thryonomys swinderianus and the small cane rat T. gregorianus. Despite their names both are large, weighing about 15 lb, and are an important food source for local people. The great cane rat is semi-aquatic and nocturnal, living in reedbeds and similar areas. It is very common within its range. The small cane rat is restricted to the wet savanna areas of Central Africa and lives in family groups for at least part of the year (Alderton). |
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