Spiny rats

(Echimyidae)

Class Mammalia

Order Rodentia

Suborder Hystricognathi

Family Echimyidae

Thumbnail description
Rat- to cat-sized rodents with large heads, and (in many species) spines in the fur of their backs; even species lacking spines, however, have another echimyid character: the presence of only four toes and a vestigial pollex (thumb)

Size
Head and body 4.13–18.9 in (10.5–48.0 cm); tail 0.2–16.5 in (0.5–42.0 cm); weight 0.46–2.9 lb (210–1,300 g)

Number of genera, species
20 genera; 78 species

Habitat
Rainforests, savannas, agricultural habitats, swamps, parks, and beach vegetation

Conservation status
Extinct: 3 species; Critically Endangered: 1 species; Vulnerable: 5 species; Lower Risk/Near Threatened: 9 species; Data Deficient: 5 species

Distribution
Central and South America

Evolution and systematics

The Echimyidae is one of the families of rodents with an evolutionary center in South America, and members of the family are still actively speciating in several genera (especially Proechimys). Four genera formerly present in the West Indies became extinct by the nineteenth century. The family shows remarkable convergent evolution with other rodent lineages, including a giant spiny rat (Chaetomys) that so closely resembles a porcupine that zoologists classified it with porcupines for many years until its true affinities were recognized. One of the most abundant and successful families of Neotropical mammals, virtually every type of lowland habitat has at least one echimyid species in it, and many have more than six. Though the least specialized echimyid genera (such as Proechimys and Hoplomys) have spines, the evolutionary trend within this family is to lose these. Thus, the more advanced and specialized genera lack spines in their fur. Fossil echimyids are known from the late Oligocene to Miocene and Pleistocene to recent. Several fossil forms reached considerable size. The family is closely related to the Capromyidae (Hutias) by the now-extinct Heteropsomyinids, the Caribbean spiny rats.

Physical characteristics

With the exception of those in the genera Isothrix and Trichomys and those in the subfamily Dactylomyinae, all

members of this family have spines in their fur, most notably on the mid-back and rump. Each spine consists of a single modified hair, and may be fine and needle-like or broad and stout. No matter what their shape or size, these spines narrow at the base to a narrow waist where they emerge from the skin.

The forefoot characteristically has only four functioning toes, with the fifth (the pollex, equivalent to the human thumb) being vestigial. The head is often large in proportion to the body, the nose is prominent, and the snout is blunt. The ears are small in proportion to the body. Many terrestrial genera have the ability to shed their tails. The family name is derived from the Greek ekhinos, a hedgehog, and mus, a mouse.

Distribution

Southern Honduras to northern Argentina.

Habitat

Primarily rainforest, though there are also species (e.g., Caterodon and Trichomys) adapted to more open and seasonally deciduous habitats.

Behavior

Generally nocturnal and burrow-using. Limited sociality, though Clyomys is colonial. Arboreal echimyid species use calls rather than scent marks to denote territories, a characteristic that is unusual in rodents.

Feeding ecology and diet

Members of this family are mostly unspecialized vegetarians, with some insects being eaten. Some species (e.g., Kannabateomys amblyonyx) have become specialized feeders on bamboo.

Reproductive biology

Echimyids do not follow the familiar rodent pattern of producing many low-investment young. Instead the litter size is small, the young are born well developed, and parental care is strong.

Conservation status

The IUCN lists one species as Critically Endangered (Makalata occasius); five species as Vulnerable (Chaetomys subspinosus, Clyomys bishopi, Diplomys rufodorsalis, Echimys chrysurus,

E. thomasi); nine species as Lower Risk/Near Threatened (Carterodon sulcidens, Diplomys caniceps, Echimys blainvillei, Isothrix bistriata, I. pagurus, Olallamys albicauda, O. edax, Proechimys albispinus, P. gorgonae); and five species as Data Deficient (Dactylomys peruanus, Echimys pictus, E. rhipidurus, Mesomys didelphoides, M. obscurus).

Significance to humans

Some species are hunted, and others are considered agricultural pests. Several species have been used as laboratory animals and some of the rarer ones have been used as flag-ship conservation species for habitat preservation.

Species accounts

List of Species

Spiny rat

Proechimys semispinosus

subfamily

Eumysopinae

taxonomy

Echimys semispinosus (Tomes, 1860), Esmeraldas, Ecuador.

other common names

German: Igelratten; Spanish: Sacha cui (Peru); Surinamese: Maka alata.

physical characteristics

The size of a house rat or white lab rat, but with a proportionately larger head and smaller ears. Fur (especially on the back and rump) is bristly to the touch due to the presence of stiffened, flattened hairs. Above is an orangish brown, and below is pure white. The tail is naked and is often pale toward the end. A weakness in the fifth vertebra of the tail means that, like lizards, Proechimys rats can break off the tail as distraction technique against predators. A rare recessive gene means that some "spiny" mice actually lack spiny fur.

distribution

Southern Honduras to coastal Colombia and Peru, only west of the Andes in South America.

habitat

Forest, often near waterways. Prefer dense vegetation, especially around treefalls.

behavior

P. semispinosus does not dig its own burrow, but uses available depressions, including cavities in rocks, holes in logs, or burrows of other animals. This species is nocturnal, with a small home range, 0.2–3.7 acres (0.1–1.5 ha), with that of the female being smaller than the male's range. Population density fluctuates seasonally, nearly quadrupling at the end of the rainy season. There is considerable overlap in home ranges, with only burrows specifically defended, and only against members of the same species and sex. Females make a variety of birdlike twit-terings to their young as they follow her around the territory.

feeding ecology and diet

Members of this family are important seed predators, eating both fallen fruit and the cached fruit of agoutis and acouchis. They also feed on fungi, including those fungi with symbiotic mycorrhizal associations with forest trees. For such fungi, they act as important dispersal agents. Members of this species will habitually take foods back to the same spot to eat them, resulting in small piles of debris that, when collected, can reveal to biologists what the animals have been eating.

reproductive biology

Opportunistic breeders, these animals will breed throughout the year if conditions permit. The litter size ranges between three and six young, a large litter for an echimyid. However, in typical echimyid fashion, the young are large (birth weight 0.7 oz, or 22 g), though not as well coordinated and furred as in other genera. The estrous cycle lasts some 23 days, and gestation is 60–65 days. Weaning occurs in three to four weeks and puberty is reached in five months. Wild individuals commonly survive more than two years. Often the most numerous terrestrial mammal in a rainforest, Proechimys species provide important food sources for small carnivores such as ocelots and jaguarondis as well as for bushmasters and other snakes.

conservation status

Not threatened.

significance to humans

Trapped for meat by rural residents.

Armored rat

Hoplomys gymnurus

subfamily

Eumysopinae

taxonomy

Echimys gymnurus (Thomas, 1897), Cachavi, Esmereldas Province, Ecuador.

other common names

English: Thick-spined rat; German: Lanzenratte; Spanish: Rata espinosa.

physical characteristics

Head and body length 8.6–12.5 in (22–32 cm); tail 5.9–9.8 in (15–25 cm); weight 7.7 oz to 1.7 lb (218–815 g). Males are considerably bigger (up to 38%) than females. This terrestrial

rodent has very thick and well developed spines, especially on its back where they are up to 1.1 in (3 cm) long and 0.08 in (2 mm) in diameter. Spines on the back are white at the base and tipped with black. On the flanks, they are tipped with orange and banded to the base with dusty orange and black. The spines are loosely fixed to the skin and fall out when the pelage is brushed the wrong way. There is soft fur interspersed with the spines and lying beneath them. Spines are most strongly developed on the mid-back, rump, and thighs. The belly lacks spines and is white. Members of this species can drop their tails to distract predators.

distribution

Southern Honduras through western Colombia to northwest Ecuador. Not found east of the Andes.

habitat

Hoplomys gymnurus lives in grassy clearings in rainforest, brush, and deserted farm lands, and has not been recorded at altitudes above 2,625 ft (800 m). The species shows a distinct preference for cooler moist areas, and in dryland forests is found only in forests in moister steep ravines.

behavior

The territory is very small and is often centered around a decaying log, under which it may hide in the burrow it digs. This consists of a small chamber with dry leaves at the bottom of a short simple shaft. This species makes runways in dense vegetation.

feeding ecology and diet

The diet consists of fruits, seeds, and browse, but insects are also eaten.

reproductive biology

Litter size of two to three. Reproduction is seasonal. Young are born furred, with open eyes and the ability to walk. This species may be monogamous, with a territory shared by a mated pair.

conservation status

Not threatened.

significance to humans

None known.

Cerrado rat

Carterodon sulcidens

subfamily

Eumysopinae

taxonomy

Echimys sulcidens (Lund, 1841), Lagoa Santa, Minas Gerais, Brazil. First described in 1841 from remains in fossil owl pellets. The first live specimen was found in 1851. Very few have been found since.

other common names

None known.

physical characteristics

Head and body length 6.1–7.9 in (15.5–20 cm). Tail 2.7–3.1 in (6.8–8 cm). Yellow-brown above, flanks grayish, with a reddish throat and neck. Under parts are yellowish with a white mid-line blotch. The tail is thin, and black above and pale yellow below. Fur on the back has spines and bristles. Spines are flexible and end in long hairlike projections.

distribution

The central uplands of Brazil.

habitat

Cerrado vegetation (a grassland with sparse trees and seasonal rains that looks a lot like the African savanna).

behavior

This species digs a shallow burrow in soil between pockets of dense vegetation, and lines this burrow and the chamber at the bottom with leaves and grasses. Emerges late afternoon or early evening to feed.

feeding ecology and diet

Not known. May feed on roots and herbs.

reproductive biology

Breeds in late dry season. Further information is not yet known.

conservation status

Near Threatened.

significance to humans

None known.

Toro

Isothrix bistriata

subfamily

Echimyinae

taxonomy

Isothrix bistriata Wagner, 1845, Río Guaporé, Brazil.

other common names

English: Yellow-crowned brush-tailed tree rat.

physical characteristics

Fur long and soft, no spines. Upperparts are yellowish gray, orange, or pale yellow below. Head has a pale yellow crown, extending onto neck. Below this is a wide black stripe that nearly merges on nape. The tail is long and thickly furred, with orange-yellow fur closer to the rump and black toward the end. Feet are short and broad with strong claws.

distribution

Amazon and Orinoco basin rainforests, as well as eastern Peru and Bolivia.

habitat

Primary forest, near streambanks.

behavior

This species is nocturnal, and feeds in trees in a squirrel-like manner. It dens in a hole in a small tree (often a dead palm) some 33 ft (10 m) from a favored tall tree, and spends afternoons with its head sticking out of the den hole. Some levels of sociality are possible, as small groups have been observed foraging together.

feeding ecology and diet

Nothing is known.

reproductive biology

Little known. Litter size is probably one.

conservation status

Lower Risk/Near Threatened.

significance to humans

None known.

White-faced arboreal spiny rat

Echimys chrysurus

subfamily

Echimyinae

taxonomy

Myoxus chrysurus (Zimmerman, 1780), Suriname.

other common names

Portuguese: Conoco, sauia banderira.

physical characteristics

Fur is bristly and spiny, with the upper parts brownish red, while the belly and throat are buff colored. A broad white blaze runs from the nose to behind the ears. The last three-quarters of the tail is white with a yellowish tip. Paws are white.

distribution

Guanas and northeastern Brazil.

habitat

In dense vegetation along riverbanks and in flooded areas. Uses upper stories of vegetation.

behavior

The same size as a familiar European/North American squirrel, but does not move like one, slinking along branches rather

than bounding. This species builds nests of dry leaves in hollow trunks or tree holes, and usually maintains two holes. Echimys chrysurus is nocturnal, and may live in small groups, which may be an extended family. Individuals give loud territorial calls at night.

feeding ecology and diet

Nothing is known.

reproductive biology

Young born fully furred and with eyes open. Litter size one or two.

conservation status

Vulnerable.

significance to humans

None known.

Amazon bamboo rat

Dactylomys dactylinus

subfamily

Dactylominae

taxonomy

Echimys dactylinus (Desmarest, 1817), upper Amazon.

other common names

English: Singing rat; Spanish: Cocopitzu (Ecuador), pacamama (Peru).

physical characteristics

The head and body are 11.8 in (30 cm), with a tail measuring approximately 15.7 in (40 cm). Weight is 1.3–1.7 lb (600–750 g). Stocky in appearance with square muzzle. Head is grayish beige with darker stripe between ear and eye. Back and flanks are grayish with a rusty wash, grading to pure rusty orange on base of tail and thighs. Underfur is black, and belly, chest and throat are white. The fur is soft and lacks spines and bristles. Only the base of the tail is haired. The paws are remarkably primate-like, with the third and fourth digits expanded in length and width for climbing (hence the genus name, which means "hand mouse"). Unlike almost all other rodents, the underside of the paws lack pads, and are broad and covered with hundreds of grip-enhancing, stud-like tubercles. Males have a gland in middle of the chest, which imparts a strong musky smell. The eye has a horizontal pupil, like a goat.

distribution

Lowland Amazon of southern Colombia, Eastern Ecuador, Peru and Brazil. Other members of the genus are known to occur in altitudes up to 5,900 ft (1,800 m).

habitat

Formerly in thick vegetation of tree falls and along river sides, this species is now common in forested areas disturbed by logging. Shows a strong preference for areas rich in vines and bamboo clumps.

behavior

This species is nocturnal, beginning activity at dusk and finishing before dawn. It spends the day in vine-rich vegetation, and has two to three regular resting sites, often in leaf masses caught in palm crowns. The home range is small, recorded as 0.6 acres (0.23 ha). Movements are slow and cautious, and this species does not move far per night—as little as 148 ft (45 m). Dactylomys dactylinus occurs in pairs, and both sexes give a staccato territorial "boop...boop...boop" call during the evening. The call, amplified by the unusually enlarged larynx, is a series of deep-pitched staccato pulses well-adapted to maximum propagation in dense vegetation. The male does much of the calling, though a pair may duet. Calls are especially common in early evening, an hour or so after dusk. Males mark stems with the chest gland. If two males meet, they will make an "explosive quacking," as an appeasement call.

feeding ecology and diet

Eats young bamboo shoots, leaves, and stems, plus a variety of other plants and fruits, and some insects. The gut has an enlarged large intestine with a pseudo-caecum. This increases the passage time of food and allows more energy and nutrients to be extracted. At 1.3–1.5 lb (600–700 g), Dactylomys is the smallest of the Neotropic's specialized arboreal folivores; if it were any smaller, it would not be able to offset the heat loss from a small body with the slow rate at which energy is received from its poor-quality food.

reproductive biology

Litter size is two.

conservation status

Not threatened.

significance to humans

The object of or a character in a number of local legends.

Southern bamboo rat

Kannabateomys amblyonyx

subfamily

Dactylominae

taxonomy

Dactylomys amblyonyx (Wagner, 1845), São Paulo, Brazil.

other common names

German: Bambus-Fingerratte; Spanish: Rata de las Taquaras (Argentina).

physical characteristics

An individual Kannbaetomys amblyonyx weighs up to 1.3 lb (600g), and its back, flanks, and head are a dull orangey-buff, while its under parts are off-white. Fur is thick and soft, lacking bristles, and the tail is thickly haired. The third and fourth digits are greatly elongated and expanded to provide a wide, strong grip when climbing thick round bamboo stems. Claws are modified into nails. The muzzle is squarish.

distribution

Southeastern Brazil (Cerea, Rio Grande, Parana, and Rio Grande do Sul), northeastern Argentina (Missones Province), and southeastern Paraguay.

habitat

Bamboo thickets along stream banks.

behavior

Kannbaetomys amblyonyx is nocturnal, solitary, slow moving, and highly territorial. The species makes loud territorial calls, defending its patch of bamboo. Individuals are found outside bamboo stands only when moving from one patch to another (every few years, plants in a bamboo stand will flower simultaneously and then die). If found on the ground in their territory, they are avoiding troops of foraging capuchin monkeys (Cebus apella), which may harass them and even kill them. There is no overlap in territories of individuals. The home range size varies from 1,780 to 11,820 ft² (165–1,098 m²). Radio-collared individuals traveled an average of 843 ft (257 m) a night. In native Guada bamboo, K. amblyonyx is reported to make large, complex nests. In stands of introduced bamboo they do not make nests, but have three to four regular resting sites in dense patches of stems and leaves. They leave and enter such areas half an hour before sunset and sunrise. The animal's slow movements and small territory size are reflective of its poor-quality food.

feeding ecology and diet

Climbs bamboo stems during the night to eat succulent shoots, young stems, and young leaves. Prefers the native giant bamboo Guada, but is also able to eat the introduced Phyllostachys and Bambusa tuloides.

reproductive biology

Litter size one or two. Subadults may travel with mother for a period after weaning.

conservation status

Not threatened.

significance to humans

Formerly considered to be threatened by habitat destruction, but now considered to be more adaptable and capable of using alien bamboos. Is being used by conservation groups as a charismatic species to promote conservation of groves of native giant bamboo and the rich bird fauna (27 habitat specific species) associated with this habitat, and who are less adaptable than the bamboo rat.

Montane bamboo rat

Olallamys albicauda

subfamily

Dactylominae

taxonomy

Thrinacodus albicauda (Günther, 1879), Medellin, Antioqua Department, Colombia. Thrinacodus had been used since the animals' original description until American zoologist Louise Emmons pointed out that this name had already been given to a fossil shark. Under the rules governing the naming of animals, no two may share the same name, so the species was given a new name. The new name celebrated the Ecuadorian collector Carlos Olalla and his four sons Alfonso, Manuel, Ramón, and Rosalino, who collected mammals all over the Amazon and elsewhere in South America between 1922 and 1969.

other common names

None known.

physical characteristics

Seven to 9.5 in (18 to 24 cm) in body length, with a tail up to 13.7 in (35 cm). Fur on the back and flanks is reddish, and the belly fur is yellowish white. The thick soft fur lacks spines, but possesses other internal characteristics of the family.

distribution

Northwest and central Colombia.

habitat

Groves of Chusquea bamboo in the montane forests of the Colombian Andes, 6,560–7,550 ft (2000–2,300 m) in altitude.

behavior

Nocturnal and arboreal, with the long tail used as a balancing pole. These animals make a whistling cry.

feeding ecology and diet

Nothing is known.

reproductive biology

Nothing is known.

conservation status

Lower Risk/Near Threatened due to habitat destruction.

significance to humans

None known.

Thin-spined porcupine

Chaetomys subspinosus

subfamily

Chaetomyinae

taxonomy

Hystrix subspinosa (Olfers, 1818), Cameta, Para, Brazil. Formerly classed with the Neotropical porcupines (Erythrozontidae), but now recognized as an echimyid and as a remarkable example of parallel evolution. Characteristics that led to this reassessment included the retention of deciduous premolars throughout life and the lack of an internal carotid artery.

other common names

None known.

physical characteristics

Rabbit-sized and weighing some 2.87 lb (1.3 kg), C. semi-spinosus has its back covered with long thin bristles. On the head, neck, and shoulders, these are more spine-like. Like sloths, this species has low levels of muscle mass for its body size.

distribution

A small portion of Atlantic Coastal Rainforest in southeastern Brazil, in the states of Sergipe, Bahia, Espirito Santo and Rio de Janeiro. Not seen after 1952, but was rediscovered in 1987.

habitat

Rainforest and secondary scrub, cocoa plantations.

behavior

Nocturnal, arboreal, solitary, and slow moving. Spends the day asleep and nearly 70% of the night resting between bouts of moving, feeding, and grooming. Tail is probably not fully prehensile, but capable of a tight grip and so assists in climbing. Like a sloth, descends to ground to defecate and urinate. Lethargic life in keeping with ingestion and digestion of poor quality, hard-to-digest forage.

feeding ecology and diet

Leaves, plus some insects and fruit.

reproductive biology

Nothing is known.

conservation status

Vulnerable. However, ability to live in modified habitats may mitigate the fact that it has a very restricted distribution in an area of very rapid deforestation.

significance to humans

None known. Eats cocoa pods but punitive hunting not reported.

Resources

Books

Eisenberg, J. F., and K. H. Redford. Mammals of the Neotropics. Vol. 3, The Central Tropics: Ecuador, Peru, Bolivia, Brazil. Chicago: University of Chicago Press, 1999.

Emmons, L., and F. Feer. Neotropical Rainforest Mammals: A Field Guide. 2nd ed. Oxford: Chicago University Press, 1997.

Periodicals

Adler, G. H., M. Endries, and S. Piotter. "Spacing Patterns within Populations of a Tropical Rainforest Rodent, Proechimys semispinosus) on Five Panamanian Islands." Journal of Zoology (London) 241 (1997): 43–53.

Adler, G. H., D. C. Tomblini, and T. D. Lambert. "Ecology of Two Species of Echimyid Rodents (Hoplomys gymnurus and Proechimys semispinosus) in Central Panama." Journal of tropical Ecology 14 (1998): 711–717.

Chiarello, A. G., M. Passamani, and M. Zortea. "Field Observations of the Thin-spined Porcupine, Chaetomys subspinosus) (Rodentia; Echimyidae)." Mammalia 61 (1997): 29–36.

Emmons, L. H. "Morphological, Ecological and Behavioral Adaptations for Arboreal Browsing in Dactylomys dactylinus (Rodentia; Echimyidae)." Journal of Mammalogy 62 (1981): 183–189.

Patton, J. L., and L. H. Emmons. "A Review of the Genus Isothrix (Rodentia; Echimyidae)." American Museum Novitates 2817 (1985): 1–14.

Stallings, J. R., M. C. Kierulff, and J. F. B. M. Silva. "Use of Space and Activity Patterns of Brazilian Bamboo Rat Kannabateomys amblyonyx) in Exotic Habitat." Journal of Tropical Ecology 10 (1994): 431–438.

Adrian A. Barnett, PhD