Scaly-tailed squirrels

(Anomaluridae)

Class Mammalia

Order Rodentia

Suborder Sciurognathi

Family Anomaluridae

Thumbnail description
Squirrel-like animals with a flexible furred membrane between the fore- and hindlimbs (except in one genus); long, silky fur and very long whiskers; long tail with two rows of pinecone-like scales one-third of the way along the underside

Size
Anomalurus: Head and body 7.3–18.5 in (18.5–46 cm); tail 5.4–18.4 in (13.8–45); weight 7 oz.–4 lb (200–1,800 grams); Idiurus and Zenkerella: Head and body 2.5–9 in (6.5–23 cm); tail 2.7–6.6 in (7–17 cm); weight 0.5–7.8 oz (14–220 g)

Number of genera, species
3 genera; 7 species

Habitat
Open dry forest and rainforest

Conservation status
Lower Risk/Near Threatened: 4 species

Distribution
Africa

Evolution and systematics

Anomaluridae is an exceedingly ancient rodent family, with a lineage extending back some 30 million years (late Eocene). Formerly much more diverse, some 20 fossil genera have been identified. The external resemblance to squirrels is misleading and, instead, anomalures are thought to resemble closely the rodent stock from which today's porcupines, rats, and squirrels are descended. Anomalures are an evolutionary enigma, very ancient and yet at the same time highly specialized. The anomalure lineage is thought to have survived for so long because they have specialized in a substance that is easily found but that few other mammals can eat: tree bark. Their family name, means "the strange-tailed ones." All members use the furred membranes for gliding between trees, sometimes very adeptly. This ability is thought to have arisen originally for moving between the widely spaced trees of dry seasonal forests, not unlike today's Brachystegia "miombo" woodlands. A pliable fur-coated membrane extends between the legs and also extends between the hind legs and the tail. The presence of a similar membrane in 14 genera of flying squirrels (Aeretes, Aeromys, Belomys, Biswamoyopterus, Eupetaurus, Glaucomys, Hylopetes, Iomys, Petaurillus, Petaurista, Petinomys, Pteromys, Pteromyscus, Trogopterus) and the marsupial genus Petaurus is a remarkable example of convergent evolution.

The systematic position of this family has been much debated. In the past they have variously been grouped with Old World porcupines, the mouse-related rodents, and the squirrel-related rodents. Sometimes, they are included in the separate suborder, Anomaluromorphia, and superfamily, Anomaluroida. This also includes another family, the Zegdoumyidae, which is extinct. Unlikely as it may seem, the closest relative to the anomalures may well be the springhare (Pedetes capensis), a thoroughly terrestrial resident of southern Africa's semi-arid grasslands. It too has a very ancient lineage.

Physical characteristics

There are two major forms in this family, the large anomalures and the smaller flying mice (one of which cannot fly). With their roughly square gliding membranes extended, members of the former group may be larger than a tea tray, while in the same condition the latter are smaller than the cover of a paperback novel. A cartilaginous extension of the elbow keeps the flying membrane rigid, while allowing the front limbs greater freedom for manipulative tasks. This strut is one of the anomalurids' unique features. The membrane, though thickly furred on top, is relatively sparsely furred on the underside. Eyes are large and forward facing, providing excellent biocular vision. Hearing is acute and may extend to ultrasonic frequencies. The two rows of spiked scales under the tail act as anti-skid devices on landing and also provide extra grip during climbing, or support while resting vertically on a trunk. For extra grip, claws are robust and sharp. The membrane is very flexi ble, and forms a loose folded extension of the flank when not in use. It does not hinder movement and all anomalurids can run along branches like the garden-familiar Sciurus squirrels. Anomalures do not come voluntarily to the ground. When placed on it they are clumsy, moving away in clumsy kangaroo-like hops.

Distribution

Anomalurids live in Africa south of the Sahara, but are absent from southern Africa.

Habitat

These animals live in the rainforests of West and Central Africa and the open drier woodlands of East Africa. The anomalures' distribution closely maps the distribution of five of the most preferred food trees: Brachystegia (miombo), Cynometra (ironwood), Dialium (velvet tamarind), Julbernadia (awoura), and Pentaclethra (owala oil).

Behavior

They are the only gliding mammals in Africa and fulfill a similar ecological role to gliding squirrels elsewhere. Anomalures remove small branches that obstruct their traditional gliding lines out from their denning tree. The long duration of the Anomalure lineage has led to some remarkable examples of coevolution with the tree species they feed on, including the deliberate gnawing off of the tops of any young non-food trees nearby, thus reducing competition with their food trees and favoring food tree growth. Anomalures and hornbills compete for dens/nest holes. Eagles are occasional predators. Scent is important in communication and large glands in the groin region produce a variety of strong-smelling secretions. Field studies of anomalures have been made difficult by the remoteness of their habitat and by the fact that they are sensitive to the red light biologists usually use to observe nocturnal animals. Anomalures are not rare, but they are hard to find. Recent population estimates in the Foret des Abeilles, central Gabon, indicate that there may be up to 500 anomalures (of three species) per 1.2 mi² (1 km²).

Feeding ecology and diet

The large anomalures gnaw bark and small branches from more than a dozen types of tree. They may also eat gum and insects. The smaller ones (flying mice) are believed to eat insects and gum almost exclusively. Bark is a low-nutrient food source. To compensate, anomalures have long guts, allowing the extraction of the maximum nutrients. These comprise half the weight and much of the body volume of an adult anomalure. Gut contents regularly exceed 12% of body weight. In order that they may still glide effectively, the anomalure skeleton is very lightweight.

Reproductive biology

The young are born with thick fur and open eyes (precocial). Litter size may be up to three. They are weaned onto solid food via finely chewed food held in the parents' cheek pouches.

Conservation status

Four species are Lower Risk/Near Threatened (Anomalurus pelii, Idiurus zenkeri, I. macrotis, and Zenkerella insignis). The remaining three species are not threatened.

Significance to humans

Occasionally accused of robbing oil palms for their nuts, but not regarded as a major pest. The large anomalures are highly dependent on particular species of tree and require tall trees, with a clear sub-canopy and enough old trees to provide an abundance of holes. Hence they are vulnerable to habitat disturbance. Many of their food tree species are valued commercially for timber.

Species accounts

List of Species

Lord Derby's anomalure

Anomalurus derbianus

subfamily

Anomalurinae

taxonomy

Pteromys derbianus (Gray, 1842), Sierra Leone. One of the subspecies of A. derbianus in the Congo, is occasionally given species rank as A. fraseri. Sixteen subspecies.

other common names

English: Lord Derby's scalytail; French: Ecureuil volant de Derby; German: Gemeines Dornschanz-hornchen.

physical characteristics

Physical characteristics vary geographically over its range, with the dorsal fur varying from gray to rich russet grizzled with silver. The subspecies, though all share the characteristic facial pattern of white snout, forehead, and cheeks, with a black band above the nose, around the eyes and back of the head. Head fur is dense and velvety, body fur long (to approximately 1 in [or 25 mm] or more) and silky. The tail is shorter than the head and body. The last half of the tail is generally black. The ears are naked and pink. There are six pairs of tail scales.

distribution

Widely distributed from western Sierra Leone to west Kenya and, more sparsely, from north Angola to northern Mozambique.

habitat

From sea level to 7,875 ft (2,400 m) in moist rainforests and seasonally dry woodlands, wherever forest provides food trees, refugia, and denning holes. Studies in the rainforests of Gabon found that most roosting trees were hollow with both basal and high holes. The high hole was often only just big enough to squeeze an anomalure body through. There was no preference in tree species.

behavior

Up to eight animals may share a den, and individuals show fidelity to a particular den for many seasons. Social behavior of A. derbianus remains to be studied. Den may be up to 130 ft (40 m) up, always in a hollow in an old tree. Used holes may vary in diameter from 1 to 8 ft (0.3–2.5 m). In the den, humidity varies little (90–95%) and temperature is also fairly constant (66–77°F [19–25°C]).

Although predominantly nocturnal, anomalures enjoy sunbathing in the early morning and, to a lesser extent, in the late afternoon. Vocalizations include a variety of social purrs and twitters and a series of defensive growls and hisses. Long-distance movement is by gliding, with speed checked before alighting by a final upturn to induce a stall. A. derbianus has been reliably measured as having glided 820 ft (250 m). An adult female, radio-tracked in a Gabonese rainforest, traveled an average of 1,770 ft (540 m) per night, with most glides being less than 328 ft (100 m). The total home range was less than 8.6 acres (3.5 ha). A male averaged 3,480 ft (1,060 m) per night and used an area of 22.8 acres (9.25 ha).

feeding ecology and diet

Diet consists of the bark of a dozen species of trees, leavened with fruits, flowers and nuts. Occasional insectivory also recorded. Thick bark from large limbs and the main trunk is preferred. A. derbianus will maintain several simultaneous feeding sites. At each, it will remove a single narrow strip adjacent to that from the previous night's feeding. Action at a particular site is curtailed when damage gets too extensive (beyond about 5.9 in [15 cm] wide). Feeding sites are initiated at natural bark wounds caused by growth splits and falling branches and by elephant damage. The trees are physiologically adapted to the rodent's depredations and grow replacement bark. In the rain-forests of Gabon, an individual of the subspecies fraseri was found to have substantial volumes of termites in its stomach. Bark is sometimes scraped away and just the oozing phloem sap licked up while the bark is ignored. Such wounds may be revisited for the insects they attract.

reproductive biology

Reproduction is seasonal for dry-forest subspecies, but not so for those inhabiting rainforests. Females may move to a special nursery den. Young are large and capable of coordinated movement soon after birth, but they remain in the nest until almost fully grown. After weaning, they are fed chewed-up food, brought in the cheek pouches of their parents. Females have also been observed gliding in the forest in the company of nearly full-grown young. Three animals were once observed gliding repeatedly between trees and chasing each other as if in play.

conservation status

Despite its specializations, the species is widely spread enough not to be threatened. Population in Ghana are on CITES Appendix III.

significance to humans

None known.

Pel's anomalure

Anomalurus pelii

subfamily

Anomalurinae

taxonomy

Pteromys (Anomalurus) pelii (Schlegel and Muller, 1845), Dubacrom, Ghana.

other common names

English: Pel's scaletail; French: Ecureuil volant de Pel; German: Pel Dornschwanz-hornchen.

physical characteristics

The largest anomalure, Pel's all-black back and pure white belly are quite distinctive. The fur on the head is black, and the snout and fur at the bases of the ears is white. The tail is white and as long as the head and body, with a thickened brush of fur on the last half. The gliding membranes are black in some subspecies and white in others. There are six pairs of tail scales. They are especially well developed in this species.

distribution

Liberia to Ghana, West Africa.

habitat

Lowland moist rainforests only, with a preference for forests with palms and tall emergent trees.

behavior

Dens may contain up to six animals. Highly nocturnal, A. pelii emerges only well after sunset, and is aggressive, using deep hoots as contact calls. Defensive noises include growls, hisses and tooth-chatterings, which the den hole may serve to amplify.

feeding ecology and diet

Supplements diet of bark with palm fruits. Observed eating leaves, twigs, and flowers of Antiaris toxicaria, an important timber tree in Ghana.

reproductive biology

Litter size of three. Two litters a year.

conservation status

The IUCN considers the species to be Lower Risk. Population in Ghana is on CITES Appendix III.

significance to humans

Sometimes blamed for damage to oil palm crops.

Beecroft's anomalure

Anomalurus beecrofti

subfamily

Anomalurinae

taxonomy

Anomalurus beecrofti Fraser, 1853, Bioko, Equatorial Guinea. This species is sometimes placed in its own genus Anomalurops, which means "closely resembling Anomalurus." It was named for John Beecroft, an Englishman who was made Governor by the Spanish of their colonial possession of Fernando Po.

other common names

English: Narrow-snouted scalytail; French: Ecureuil volant de Beecroft; German: Beecroft Dornschwanz-hornchen.

physical characteristics

Snout, and head generally, markedly narrower than other anomalures. Tail proportionately much shorter and narrower than other species of anomalure. Tail has nine pairs of tail scales. A species with a wide range and corresponding geographical variation. Dorsal colors range from gray to rich red or orange. The belly is always some shade of orange-yellow and the head always has a white spot (of variable size) in the middle of the forehead.

distribution

Southern Senegal to eastern Democratic Republic of the Congo.

habitat

Rainforest, from sea level to 8,200 ft (2,500 m). Also cultivated palm groves and disturbed land if some big trees remain.

behavior

Probably a species that, in undisturbed forest, makes use of natural tree falls and the palms that grow up in them. Much less dependent on deep forest than the other anomalures, this species can occur in agricultural areas. Quite often active during the day. Females with young build nests of leaves in tree holes. Males and non-reproducing females may hide during the day beneath large branches or at the basal junction of a palm's frond and trunk, or may crouch flat against a trunk. Members of this species may take palm nuts back to the den to peel and eat.

feeding ecology and diet

Less dependent on bark than other anomalures. Though eaten, bark is less important than fruits (especially those of palms). Some leaves and insects are also eaten.

reproductive biology

Not known. A female with a single embryo has been collected.

conservation status

Not considered to be threatened. Population in Ghana is on CITES Appendix III.

significance to humans

Occasionally blamed for loss of palm fruits, but not hunted punitively.

Lesser anomalure

Anomalurus pusillus

subfamily

Anomalurinae

taxonomy

Anomalurus pusillus Thomas, 1887, Democratic Republic of the Congo.

other common names

English: Dwarf scalytail; French: Ecureuil volant de pygmlbée; German: Zwergdornschwanz-horchen.

physical characteristics

The smallest anomalure, the coloration of A. pusillus varies from a mottled light gray and tan to very dark gray. The underside is usually a yellow-washed gray. Head is generally gray with no facial pattern. There are seven named subspecies. The tail, one-third the length of the body, generally has a black hinder third.

distribution

Three isolated populations in Senegal, Sierra Leone/Liberia and Cameroon/Gabon/Congo.

habitat

Deep primary lowland rainforest.

behavior

Little studied. Known to roost in hollow trees.

feeding ecology and diet

Bark and fruit.

reproductive biology

Nothing is known.

conservation status

Naturally rare, but not categorized as a species of concern by the IUCN.

significance to humans

None known.

Zenker's flying mouse

Idiurus zenkeri

subfamily

Zenkerrinae

taxonomy

Idiurus zenkeri Matschie, 1894, Yaunde, southern Cameroon.

other common names

English: Dwarf flying mouse; French: Ecureuil volant de Zenker; German: Zenker Gleitbilch.

physical characteristics

With a head and body less than 3.9 in (10 cm) long, this is the smallest member of the family. Weight: less than 0.5 oz (15 g). The body is buff-colored above, a gray-white below. The tail, 50% longer than the head and body, has an underside fringed with two rows of stiff hairs. Long, scraggly sparsely distributed hairs emerge from the tail's upper surface. The snout is conspicuously upturned and the oddly notched upper incisor teeth are especially long and protrude beyond the lips.

distribution

Central Africa, Cameroon, and Democratic Republic of the Congo.

habitat

Primary moist lowland rainforest.

behavior

Strictly nocturnal and little known. Recorded roosting in hollow trees in groups from three to over 100. Small colonies may also roost under bark. Believed to travel many miles (kilometers)

a night in search of food. Zenker's flying mouse is an exceptionally agile glider, capable of glides exceeding 164 ft (50m) and of intricate spirals and of S-shaped glides close to trunks. Shrill mouse-like squeaks have been reported.

feeding ecology and diet

Oil palm pulp, insects, and nectar.

reproductive biology

Nothing is known.

conservation status

Lower Risk/Near Threatened.

significance to humans

None known.

Big-eared flying mouse

Idiurus macrotis

subfamily

Zenkerrinae

taxonomy

Idiurus macrotis Miller, 1898, Efulen, Cameroon. Now believed to include the species I. kivuensis.

other common names

French: Anomalure nain; German: Grosshargleitbilch.

physical characteristics

A larger animal with darker, grayer fur than I. zenkeri. The ears are longer and black compared to the pale brown of zenkeri. The tail is only 25% longer than the head and body.

distribution

Two isolated populations. Sierra Leone, Liberia, Ivory Coast, Ghana; Cameroon, Gabon, Congo, and north eastern Democratic Republic of the Congo. No records from Nigeria.

habitat

Primary lowland rainforests, but also uses areas where local small plantations have thinned the canopy.

behavior

Recorded sharing hollow tree roosts with I. zenkeri, other anomalures, and bats. In Gabon, prefers trees with a single large basal hole. Groups of animals may use the same den for several years in a row. An adult male, equipped with a radio collar, moved through an area of 7.4 acres (3 ha) in 48 hours, traveling an average of 2,590 ft (790 m) each night. Nocturnally active, the male began moving around 15 minutes after sunset and ending at dawn. On emerging, the colony members will spend some 30 minutes running up and down the trunk of the home tree before gliding out to forage. Though always seen resting in groups, I. macrotis appears to forage alone.

feeding ecology and diet

Nothing is known.

reproductive biology

Five female I. macrotis were collected in June and August in eastern Democratic Republic of the Congo. Each had a single embryo.

conservation status

Lower Risk/Near Threatened. Populations in Ghana are on CITES Appendix III. The species is on the country Red List in Sierra Leone and Ivory Coast.

significance to humans

None known.

Cameroon scaly-tail

Zenkerella insignis

subfamily

Zenkerrinae

taxonomy

Zenkerella insignis Matschie, 1898, Yaunde, Cameroon. This rodent shares its generic name, Zenkerella, with a genus of African tree from the pea family.

other common names

English: Flightless dwarf anomalure; German: Dornscgwanzbilch.

physical characteristics

Strong resemblance to a very soft-furred dormouse. Large eyes, pink ears. Long ashy gray fur washed with dull yellow, especially on the lower limbs and cheeks. The underparts are a paler gray. Whiskers are long and shiny black. The tail is thick, with long black hairs. No flight membrane is present between limbs, but tail has the family's characteristic bark-gripping scales. There are 13 scales, one line of six and one of seven. Very little is known about this animal—less than two dozen have been caught and examined by scientists.

distribution

Known only from the western part of Central African rain-forests; Cameroon, Equatorial Guinea, Gabon, Congo, and from Bioko Island (formerly Fernando Po) in the Gulf of Guinea.

habitat

Tolerates climates ranging from relatively dry (rainfall, 59 in [1,500 mm] per year) to very humid (394 in [10,000 mm] of rain per year). Most records from lowland rainforest, with a few from seasonally deciduous forest and treed savannas.

behavior

Probably a day-active high-canopy specialist that has abandoned flight for a more scuttling progression. Very long, dense fur might cushion short leaps between trunks or branches. Must on occasion descend to the ground since has been caught in traps set for terrestrial rodents. Ankles have a brush of stiff hairs with flattened "spoon-like" tips. Associated with a patch of glands, they may serve to broadcast territorial scents, but the exact mechanism is uncertain. Rests by leaning against the interior wall of a hollow tree. Sometimes found roosting in the company of other anomalurids. Considered rare, though this may be an artifact of the remoteness of its habitat and the difficulty of studying small mammals in the rainforest canopy. In some parts of its range, the species may be nocturnal; the Bubi forest people of Bioko, who do not hunt at night, were unaware of this species.

feeding ecology and diet

Nothing is known.

reproductive biology

Basically unknown. A male collected in the dry season had fully developed testes.

conservation status

Lower Risk/Near Threatened.

significance to humans

None known.

Resources

Books

Kingdon, J. The Kingdon Field Guide to African Mammals. New York: Academic Press, 1997.

Periodicals

Adam, F., L. Bellier, and L. W. Robbins. "Deux nouvelles captures d'Idiurus macrotis Miller (Rodentia, Anomaluridae)." Mammalia 34 (1970): 716–717.

Aellen, V., H. Heim de Balsac, and R. Vuattoux. "A propos des Anomaluridae de Côte d'Ivoire." Mammalia 34 (1970): 159–160.

Aellen, V., and J. Perret. "Sur une nouvelle trouvaille de Zenkerella insignis Matschie, 1898 (Rodentia, Anomaluridae)." Saugetierkunde Mittelunde 6 (1995): 21–23.

Jones, C. "Notes on the Anomalurids of Rio Muni and Adjacent Areas." Journal of Mammalogy 52 (1971): 568–572.

Julliot, C., S. Cajani, and A. Gautier-Hion. "Anomalures (Rodentia, Anomaluridae) in Central Gabon: Species Composition, Population Densities and Ecology." Mammalia 62 (1998): 91–121.

Perez de Val, J., J. Juste, and J. Castroviejo. "A Review of Zenkerella insignis Matschie, 1898 (Rodentia, Anomaluridae). First Records in Bioko Island (Equatorial Guinea)." Mammalia 59: (1995): 441–443.

Roche, J. "Capture de Zenkerella insignis (Rongeurs, Anomaluridés) en République Central-Africaine (Equatorial Guinea)." Mammalia 36 (1972): 305–306.

Adrian A. Barnett, PhD