Family Cuniculidae
pacas

There are 2 species of cuniculids, placed in the single genus Agouti. These large, terrestrial rodents are commonly called pacas. ()

Pacas are found in Central and South America, from east central Mexico to Paraguay. ()

These rodents live along rivers and streams in tropical forests, from sea level to about 3000 m elevation. ()

Cuniculidae is also known by the name Agoutidae. Some authors have placed pacas within the family Dasyproctidae, due to morphological similarities between pacas and dasyproctids (Dasyproctidae) (Corbet and Hill 1991; Wilson and Reeder 1993). The widely recognized common name of Dasyproctidae is also "agoutis", which creates some confusion. Others have placed pacas in a separate family based on morphological evidence (Anderson and Jones 1984; McKenna and Bell 1997). Molecular evidence from two nuclear sequences and the 12S rRNA mitochondrial gene strongly supports the placement of pacas in their own family, distinct from the Dasyproctidae (Rowe and Honeycutt 2002).

Mountain pacas, Cuniculus taczanowskii, have also been known by the generic name Stictomys (Rowe and Honeycutt 2002). ()

Pacas are very large, up to around 12 kg in males. Females are somewhat smaller. They have chunky bodies, short, stout legs, hind limbs that are longer than the forelimbs, and a large, blunt head. The eyes are large and external ears are small. Pacas are nearly tailless. The forefeet have 4 functional toes, and the hindfeet 3 (digits 1 and 5 are present but reduced). The claws are thick and hoof-like. The pelage of pacas is coarse and without underfur. Dorsally, pacas are brown, with whitish spots arranged in longitudinal lines. Their bellies are whitish. ()

The skulls of pacas are unmistakeable. They are broad and massively constructed, with short nasals and long, broad frontals. A sagittal crest may sometimes be found over the posterior part of the braincase. A postorbital process is present, but it seems to be located unusually far back over the orbit. The zygomatic arches are enormously inflated, with jugal and maxillary forming a large, rough-surfaced plate on the outside and a smooth, hollow chamber on the inside. While large, the jugal does not contact the lacrimal. The infraorbital foramen is reduced in size, although these animals are hystricomorphous. A separate canal conducts nerves from the orbit to the rostrum. Pacas have small auditory bullae and long and heavily-built paroccipital processes. Lower jaws are hystricognathous, but the angular process is offset less than in many other hystricognaths. ()

The cheekteeth of pacas are hypsodont. They are flatcrowned and have a complex pattern of re-entrant folds. The first two molars have 1 labial and 3 lingual folds, while the third molar has 3 labial and 1 lingual. These folds become isolated to form enamel islands as the teeth wear. The dental formula is 1/1, 0/0, 1/1, 3/3 = 20. ()

Pacas live 12 to 13 years in the wild, and up to 16 years in captivity. ()

Pacas are terrestrial mammals, preferring the wooded banks of streams and ponds. They are good diggers, constructing burrows in banks, slopes, or among tree roots or rocks. These have several entrances that are often plugged with leaves. Pacas forage at night, following well-defined paths to feed on foliage, roots, nuts, seeds, and fruits. They are excellent swimmers, using water as a means of escaping predators, but generally they do not dive or forage in the water. Pacas are generally solitary and active at night. ()

Like most rodents, pacas perceive the world through visual, acoustic, tactile, and chemical signals. While generally solitary, they do communicate by means of vocalizations, foot thumping, and tooth grinding. It has been suggested that the hollow chambers formed by their expanded zygomatic arches are resonating chambers to amplify sounds. In captivity, pacas have been observed scent-marking their enclosures with urine and feces. ()

Pacas consume foliage, roots, nuts, seeds, and fruits. Their large cheek pouches may be used in food storage, but this is not certain. ()

The major predators of pacas are felids, including cougars, jaguarundis, margays, little spotted cats, ocelots, and jaguars. Coyotes are also important predators. Occasional predators include crocodiles, boa constrictors, and bush dogs. Pacas are excellent swimmers and retreat to the water to escape predators. ()

These plant-eating rodents are primary consumers, and they serve as prey for felids, canids, and reptiles. They likely compete for food with many species that have overlapping diets and habitats, including agoutis (Dasyprocta), squirrels (Sciurus), spiny rats (Proechimys), peccaries (Tayassu), brocket deer (Mazama), tayra (Eira), kinkajous (Potos), coatis (Nasua), woolly opossums (Caluromys), and brown four-eyed opossums (Metachirus). Pacas are parasitized by mites, nematodes, tapeworms, and protozoa. ()

Pacas may be agricultural pests in some areas. ()

Throughout their range, pacas are much sought for their flesh, which is tender and mild-flavored. ()

Both paca species are considered lower risk by the IUCN. The main threats to their populations are hunting and habitat destruction. ()