Pacaranas

(Dinomyidae)

Class Mammalia

Order Rodentia

Suborder Hystricognathi

Family Dinomyidae

Thumbnail description
Like a solidly-built, medium-dog-sized rodent with a large head

Size
Weight 22 to 33 lb (10 to 15 kg), head and body length range from 28 to 31 in (730 to 790 mm), plus a tail length of about 7.5 in (190 mm)

Number of genera, species
1 genus; 1 species

Habitat
Lowland and montane tropical rainforest

Conservation status
Endangered

Distribution
Western South America, from Venezuela into Bolivia

Evolution and systematics

Dinomys branickii is the only surviving species of the family Dinomyidae, genus Dynomys, an ancient and once varied group of South American rodents whose rat-like ancestors probably rafted on vegetation from Africa to South America between 45 and 36 million years ago (mya). The dinomyids were far more diverse in the Oligocene-Pliocene (34 to 1.8 mya). At least eight species of Dinomyidae are known from fossils, and some were the largest rodents ever to exist. The unusually large size of pacaranas recalls but merely echoes creatures like its extinct relative, Telicomys gigantissimus, as big as a rhinoceros, and, rivaling it in size, Artigasia magna. The great size of these and a few other related species gave rise to the family name, Dinomyidae, meaning "terrible mouse."

Pacaranas are hystricognath rodents, within the suborder Hystricognathi, that classification based on peculiarities of their skulls, lower jaws, and jaw muscles, shared among all member species. Hystricognath rodent species live mainly in South America and Africa, plus some species in southern Europe and Asia, and one species of New World porcupine (Erethizon dorsatum) in North America. The suborder is vast, made up of 18 families, which include the African mole rats, dassie rats, grasscutter rats, Old and New World porcupines, capybaras, chinchillas, agoutis, and many others. With few exceptions, hystricognath rodents produce small litters of one or two young; infants are precocial, i.e., born furred, with eyes open, and able to move about. Suborder Hystricognathi can

be separated into two infraorders, Caviomorpha, the New World hystricognaths, and Phiomorpha, the Old World hystricognaths.

Some taxonomists have tentatively explained the similarities of the American and African hystricognaths as resulting from convergence. Some of the latest studies in genetic and molecular evolution involve the "molecular clock" method, whereby genes from related species are sequenced and the number of mutations in neutral genes are noted, providing an estimation of the time a new species diverged from the ancestral line. As of 2001, molecular clock studies among hystricognath species on both sides of the Atlantic strongly support their sharing a common ancestor, and strongly suggest a single colonizing event of African hystricognaths to South America, in the interval of 45–36 mya, that eventually gave rise to the great diversity of New World hystricognaths, including Dinomys branickii (Honeycutt; Huchon & Douzery; Honeycutt, Nedbal & Schlitter). During the interval of 45–36 mya, the Atlantic ocean was about half as wide as it is today, and had ocean currents between the two continents that would have been favorable for a rafting and colonization event from Africa to South America. There is, however, far from universal agreement on this scenario.

The taxonomy for this species is Dinomys branickii Peters, 1873, Montana de Vitoc, Department of Junin, Peru. The pacarana was first described in Western science in 1873 by a Polish count named Branicki, who did field research on South American wildlife for the Warsaw Museum of Natural History. Other common names include false paca, Branick's giant rat, machetero ("cutter" or "chopper"), rukupi, piro, teconi, tecon, lapa rabuda, lapo, lapa cacique, guagua lanuda, and guagua loba.

Physical characteristics

An adult pacarana weighs from 22 to 33 lb (10–15 kg), with head and body length from 28 to 31 in (730–790 mm), plus a tail length of about 7.5 in (190 mm). The body is compact and heavily built, and the broad head is large in comparison to the body. The limbs are moderately short, and powerfully muscled. A fairly thick coat of coarse hair covers the body. The upperparts of the pelage are dark brown or blackish, with rows of whitish spots running the length of the body. A bushy set of long, grayish whiskers arises from the snout. The paws bear four digits apiece and as many claws.

The name of the species is derived from a Tupi Indian word meaning "false paca" referring to its overall resemblance to the paca, Agouti paca. The pacarana is the third largest living rodent, after capybaras (Family Hydrochoeridae) and beavers (Family Castoridae), its weight ranging from 22 to 33 lb (10 to 15 kg), head and body length from 29 to 31 in (730 to 790 mm), and an additional tail length of about 7.5 in (190 mm). The body is compact and heavily built, and the broad head is large in comparison to the body. The second and third vertebrae of the neck are fused. Those who have seen living pacaranas have compared them to small bears, huge guinea pigs, and porcupines robbed of their quills.

A pacarana bears a fairly thick coat of coarse hair over nearly its entire body, including the bushy tail, but excepting the nostrils and the soles of all four feet. The dorsal/upper parts of the pelage are dark brown or blackish, with four rows of whitish spots forming broken white stripes along its upper body length. Two or three rows of more randomly arranged spots decorate both flanks. The underparts are a lighter shade. Adding the final touch to the rough coat is a bushy set of long, grayish whiskers situated about midway on the upper snout. The individual whiskers can be as long as the head or longer. The ears are relatively short and round, the eyes are large, and the upper lip is deeply cleft.

All four feet are plantigrade, i.e., the entire heel rests on the ground as the animal walks or stands, and it walks with a waddling gait. Each of the four paws bears four digits, each digit fitted with a long, curved, heavy claw. The limbs are powerfully muscled and only moderately short, but the thick, hanging pelage may obscure the lengths of the limbs. All the features of the legs and feet would seem to indicate that pacaranas are diggers, but no one has ever seen a wild or a captive pacarana dig, although they may widen the entrances to their shelters with clawstrokes. They sometimes climb, and they can and will walk bipedally.

The cheek teeth of a pacarana grow continuously. The gnawing incisors are designed according to the basic rodent pattern, and they are broad and powerful.

Distribution

Pacaranas are thinly scattered in a band running through mountainous territory from western Venezuela through western Colombia, central Ecuador, Peru, a small section of western Brazil, and into northwestern Bolivia. In Peru, pacaranas live from 800 to 6,600 ft (240 to 2,000 m) above sea level, and up to 7,870 ft (2,400 m) above sea level in Venezuela.

Habitat

Pacaranas inhabit forested mountain slopes and valleys of rainforests in the Andes mountains, from 800 to 6,600 ft (240 to 2,000 m) above sea level. According to the classification of

World Wildlife Fund Global 200 Terrestrial Ecoregions, pacaranas are found in Bolivian Yungas, Southwest Amazon moist forests, Venezuelan Andes montane forests, and Magdalena Valley montane forests.

Behavior

Pacaranas are nocturnally active. Captive pacaranas are unagressive, peaceful creatures, but they are well adapted for defense and can be disconcertingly vicious. Adults are solitary or live in pairs or in family groups. Pacaranas communicate with a varied and complex array of sounds and postures.

Pacaranas have been but little studied in the wild, and much information about their behavior and biology has been learned from observing captive animals.

Captive pacaranas, most of the time, are unaggressive, peaceful creatures. Pacaranas are often the butt of jokes comparing their peaceful, pokey nature to their genus name, Dinomys, which adds up to an irony. Nevertheless, pacaranas are not only well-equipped for self-defense, but have a well-earned reputation for occasional but effective viciousness. In a Brazilian zoo, several pacaranas in an enclosure ganged up on and killed a paca introduced into the compound, the keepers probably assuming that the normally phlegmatic pacaranas would prove no threat to the new tenant. Domestic dogs living in areas inhabited by pacaranas have learned to fear and avoid them, because of the large rodents' spirited defense. This may partly explain their continued survival, despite their low numbers and density. The pacarana is a strong, fairly large animal with formidable claws and powerful limbs, and can apparently give a good account of itself in a tight spot. Nevertheless, pacaranas are vulnerable to humans, who can kill them from a distance.

In the wild, pacaranas live in cracks between rocks or in natural caves. Adults live alone, in pairs, or in family groups of a parent pair with one or more litters of their young.

Pacaranas communicate with a varied repertoire of sounds, stamping with their forepaws, tooth chattering, whining, melodious songs, and hissings. Researchers have found seven distinct pacarana vocalizations used in social situations.

Life spans of wild pacaranas are unknown, but a captive pacarana reached the impressive age, for a rodent, of nine years and five months.

Feeding ecology and diet

Pacaranas are nocturnal foragers, feeding on palm and other kinds of fruits, leaves, and young, tender stems of plants. They will sometimes climb trees in quest of edibles, aided by their strong, curved claws, but spend most of their active time on the ground. When feeding, they sit on their hind legs and hold their food with both forepaws.

Reproductive biology

Pacaranas make crying vocalizations during the breeding season to attract sexual partners. Individuals in first-time male-female encounters most often communicate with hisses,

growls, and staccato whimpering sounds. If courtship ensues, the male vocalizes with a string of whimpering notes that he may segue into singing lasting up to two minutes. As the two approach each other more closely, they touch noses, sniff genitals, and begin an elaborate contact ritual that looks like a combination of dancing and wrestling. The two stand bipedally, grappling, and interlocking their incisors. Courtship moves may include ritual head-tosses and dancing, ending at last with mounting. The male's forelegs tremble as he approaches the female, a common courtship ritual in rodents. Males may also approach bipedally, with an erect penis.

Pregnant females have been seen in February and May, while births have been observed in January and February. A pregnant female will show a sudden weight gain at about 90 days of gestation, and she can become irritable. No nest building by pregnant or postpartum females has been observed.

The gestation period of captive animals ranges from 222 to 283 days, and the common litter size is one or two. A newborn pacarana weighs about 32 oz (900 g). The infant is precocial, i.e., fully furred and able to see and move about, groom itself, and actively investigate its new world within a few days of birth. Weaning period and age of sexual maturity for pacaranas are as yet unknown.

Conservation status

As of 2002, pacaranas are classified as Endangered in the IUCN Red List of Threatened Species. Not common to begin with, their low population levels are vulnerable to hunting by humans and to habitat loss, and has several times been feared extinct.

Significance to humans

Indigenous people in South America hunt pacaranas for food.

Resources

Books

Wood, A. E. "The Relationships, Origin and Dispersal of the Hystricognath Rodents." In Evolutionary Relationships Among Rodents, A Multidisciplinary Analysis, edited by W. P. Luckett and J.-L. Hartenberger. New York: Plenum Press, 1985.

Periodicals

Boher, S., J. Naveua, and L. Escobar. "First Record of Dinomys branickii for Venezuela." Journal of Mammalogy 69, no. 2(1988): 433.

Collins, L. R., and J. F. Eisenberg. "Notes on the Behaviour and Breeding of Pacaranas, Dinomys branickii, in captivity." In International Zoo Yearbook 12 (1972): 108–114; Zoological Society of London.

Fields, R. W. "Hystricomorph Rodents from the late Miocene of Colombia, South America." University of California Publications in the Geological Sciences 32 (1957): 273–404.

Hodge, W. H. "The Not So Terrible Mouse." Natural History Magazine LVI, no. 7 (1947): 310–311.

Huchon, D., and E. J. Douzery. "From the Old World to the New World: A Molecular Chronicle of the Phylogeny and Biogeography of Hystricognath Rodents." Molecular Phylogenetics and Evolution 20, no. 2 (2001): 238–251.

Landry, S. O. "Is the Guinea Pig a Rodent?" Nature 381 (1991): 597–600.

Nedbal, M. A., R. L. Honeycutt, and D. A. Schlitter. "Higher-level Systematics of Rodents (Mammalia, Rodentia): Evidence from the Mitochondrial 12S rRNA Gene" Journal of Mammalian Evolution 3, no. 3 (1996): 201–237.

Patterson, B., and A. E. Wood. "Rodents from the Deseadan Oligocene of Bolivia and the Relationships of the Caviomorpha." Bulletin of the Museum of Comparative Zoology 149 (1982): 371–543.

Ray, C. E. "Fusion of the Cervical Vertebrae in the Erethizontidae and Dinomyidae." Breviora 97 (1958): 1–11.

White, T. G., and M. S. Alberico. "Dinomys branickii." Mammalian Species 410 (1992).

Organizations

IUCN—The World Conservation Union. Rue Mauverney 28, Gland, 1196 Switzerland. Phone: +41 (22) 999 0000. Fax: +41 (22) 999 0002. E-mail: [email protected] Web site: <http://www.iucn.org>

Other

2002 IUCN Red List of Threatened Species. <http://www.redlist.org>

Animal Diversity Web. Dinomyidae.<http://animaldiversity.ummz.umich.edu/chordata/mammalia/rodentia/dinomyidae.html>.

Paleontologia de Argentina—Periodo Plioceno. <http://ar.geocities.com/paleontologiaweb/plioceno.htm>.

SciTecLibrary.com Scientific News. "Rafting Rodents From Africa May Have Been Ancestors of South American Species." (source: Texas A & M University). <http:// www.sciteclibrary.com/eng/catalog/pages/2351.html>

World Wildlife Fund, Global 200 Ecoregions: Blueprint for a Living Planet. "List of All Ecoregions." <http://www.panda.org/resources/programmes/global200/pages/list.htm>.

Kevin F. Fitzgerald, BS