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. (Pérez, 1992; Vaughan, et al., 2000; Woods, 1984)
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. (Pérez, 1992; Vaughan, et al., 2000; Woods, 1984)
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. (Pérez, 1992; Vaughan, et al., 2000; Woods, 1984)
No information is available on the mating system of pacas. They are known to be solitary, however, which would suggest that they are polygynandrous. (Nowak, 1999)
Pacas breed throughout the year in most of their range. On the Yucatan peninsula, they mate in early winter and females give birth in winter to early spring, which is the dry season. Pacas may have up to two litters per year. Usually only one offspring is born at a time, though twins occur occasionally. The gestation period is about 118 days, after which females experience a postpartum estrus. The young are weaned at 6 to 12 weeks of age. Females begin breeding at one year old. (Nowak, 1999; Pérez, 1992; Vaughan, et al., 2000)
Like all eutherian mammals, female pacas nurture developing offspring through the placenta. After the young are born, they are provided with milk until they are 6 to 12 weeks old. Young pacas are precocial; they are born with their eyes open and they are able to walk shortly after birth. (Nowak, 1999; Pérez, 1992)
Pacas live 12 to 13 years in the wild, and up to 16 years in captivity. (Nowak, 1999)
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. (Nowak, 1999; Pérez, 1992; Vaughan, et al., 2000)
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. (Pérez, 1992; Vaughan, et al., 2000)
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. (Nowak, 1999; Pérez, 1992)
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. (Nowak, 1999; Pérez, 1992)
The fossil record of pacas begins in the Oligocene. (Vaughan, et al., 2000)
Tanya Dewey (editor), Animal Diversity Web.
Allison Poor (author), University of Michigan-Ann Arbor.
Phil Myers (earlier author), Museum of Zoology, University of Michigan-Ann Arbor.
living in the southern part of the New World. In other words, Central and South America.
uses sound to communicate
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
union of egg and spermatozoan
an animal that mainly eats leaves.
A substance that provides both nutrients and energy to a living thing.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
Referring to a burrowing life-style or behavior, specialized for digging or burrowing.
an animal that mainly eats fruit
an animal that mainly eats seeds
An animal that eats mainly plants or parts of plants.
fertilization takes place within the female's body
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
breeding takes place throughout the year
young are relatively well-developed when born
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