African Sideneck Turtles (Pelomedusidae)

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African sideneck turtles

(Pelomedusidae)

Class Reptilia

Order Testudines

Family Pelomedusidae

Thumbnail description
Medium-sized, sideneck turtles with five claws on the hind feet, four to eight neural bones present, the pleural bones almost always meeting at the midline behind the neurals, mesoplastral bones present, and the pelvis fused to the plastron

Size
Up to 21.6 in (55 cm) carapace length

Number of genera, species
2 genera; 18 species

Habitat
Freshwater habitats, from permanent rivers and lakes to ephemeral ponds

Conservation status
Vulnerable: 2 species

Distribution
Africa, Madagascar, and the Seychelles Islands

Evolution and systematics

Pelomedusidae is most closely related to Podocnemidae, but diverged from that family at least by the Cretaceous (at least 110 million years ago). Fossils are known from the Miocene to the Recent, but all belong to the two living genera. No subfamilies are recognized.

Physical characteristics

These turtles are generally small to medium in size, usually less than 12 in (30 cm), with a relatively extensive plastron that may (in Pelusios) or may not (in Pelomedusa) have a hinge present between the pectoral and abdominal scutes. The neural series is highly variable (with four to eight present), and the pleural bones almost always meet at the midline posterior to the neurals. A pair of mesoplastral bones are present between the hyo- and hypoplasta, and may (in Pelusios) or may not (in Pelomedusa) be in contact. Five claws are present on the hind feet.

Distribution

Africa up to at least 10,200 ft (3,100 m) elevation, Madagascar, and the Seychelles Islands.

Habitat

As a group, these turtles occupy nearly any freshwater aquatic system, from permanent lakes or rivers to ephemeral pools which may contain water only a few weeks at a time.

Behavior

Surprisingly little is known about the behavior of these turtles. They frequently bask at the water's edge, and several species make extensive overland movements during the wet season. During the dry season, many species estivate underground. In the temperate climates of southern Africa, they will hibernate terrestrially or aquatically. When captured, they produce a pungent musk from glands located near the bridges (bony structures that connect the plastron and carapace).

Feeding ecology and diet

These turtles are all primarily carnivorous, feeding mainly on annelids, mollusks, crustaceans, insects, fish, amphibians, and carrion. Some are at least partly herbivorous, eating water lettuce, aquatic grasses, or fruits.

Reproductive biology

No species in this family has been well studied; most of what is known is based on anecdotal reports. Most species apparently nest in late spring or summer, from October to January. The eggs are elongate with leathery shells, and clutch sizes range from six to 48. Multiple annual clutches have not been confirmed for any species, but seem likely considering the length of the potential nesting season. All species that have been studied exhibit temperature-dependent sex determination, with warm temperatures producing females, intermediate temperatures producing mostly males, and still cooler temperatures again producing females.

Conservation status

The actual field status of most of the species in this family has not been adequately assessed. The only two species listed as Vulnerable on the IUCN Red List are the two with the most restricted distributions: Pelusios broadleyi in Lake Turkana in Kenya, and P. seychellensis in the Seychelles.

Significance to humans

These turtles are occasionally eaten by indigenous people, but their foul-smelling musk secretions probably serve to discourage more regular consumption. They are also in low demand for the pet trade.

Species accounts

List of Species

Helmeted turtle
East African serrated mud turtle
East African black mud turtle

Helmeted turtle

Pelomedusa subrufa

taxonomy

Testudo subrufa Lacepède, 1788, "Indes" [in error; restricted to Cape of Good Hope]. Three subspecies are recognized.

other common names

English: Cape terrapin, helmeted terrapin; French: Roussâtre; German: Starrbrust-Pelomeduse; Afrikaans: Gewone water-skilpad.

physical characteristics

Small to medium turtles, with a maximum shell length of 13 in (33 cm), and a broad, flattened, brown to olive carapace. The plastron is rigid (i.e., unhinged), and firmly attached to the carapace. A pair of small triangular mesoplastral bones are present between the hyo- and hypoplastra, but they are widely separated.

distribution

Africa from Senegal and Ethiopia to South Africa, Madagascar, southern Saudi Arabia, and Yemen.

habitat

Helmeted turtles are semiaquatic, inhabiting ponds, marshes, and streams, as well as temporary rain pools.

behavior

These turtles commonly migrate overland between bodies of water, and therefore most frequently are seen on land or basking at the water's edge. When their habitat dries up, they estivate in

the mud until the next rains (which may be longer than a year). They hibernate terrestrially in the ground or under leaves during the winter in southern Africa. Adults feed mostly at dawn or during the night, but hatchlings forage day and night. Helmeted turtles are occasionally very aggressive in captivity.

feeding ecology and diet

These turtles are primarily carnivorous, feeding on earthworms, snails, clams, crustaceans, insects, fishes, frogs and tadpoles, small reptiles, birds, mammals, and carrion of any kind. They have even been observed to attack larger prey, such as birds, as a group, as well as to feed on the ticks on the hide of rhinoceroses when the latter enter waterholes. They also occasionally feed on various parts of aquatic plants and the fruits of terrestrial species.

reproductive biology

In subtropical environments, courtship and mating occur in the spring. The male chases the female from behind, touching or biting her posterior extremities with his head, and eventually mounting the top of her shell. He extends his head in front of hers, sways it from side to side, and expels water through his nostrils. His longer tail then swings under hers for intromission. The well-formed, flask-shaped nest is constructed in the late spring to early summer, and apparently only one clutch is laid per year. From 13 to 30 oblong, leathery eggs, averaging 1.5 by 0.9 in (38 by 22 mm) are laid in a clutch. Hatching requires 75–110 days, with hatchlings emerging in February to June. This species is known to exhibit temperature-dependent sex determination, with warm temperatures producing females, intermediate temperatures producing mostly males, and still cooler temperatures again producing females.

conservation status

This species is so widespread across Africa, occupies such a variety of aquatic habitats, and reaches such high densities that human impact has apparently not been extensive. In fact, the construction of ponds and waterholes for livestock and wildlife has benefited this species by providing new habitats.

significance to humans

This species is eaten by some indigenous people, often by roasting the whole animal under hot coals. Some groups believe the blood to have medicinal properties. The turtles are exploited only minimally for the pet trade.

East African serrated mud turtle

Pelusios sinuatus

taxonomy

Sternotherus sinuatus Smith, 1838, "rivers to the north of 25° south latitude" [South Africa]. No subspecies are recognized.

other common names

English: Serrated hinged terrapin, serrated turtle; Afrikaans: Groot waterskilpad.

physical characteristics

These turtles are medium to large size, with a maximum shell length of 2.2 in (5.5 cm), and an elongate, oval, variably

keeled, posteriorly serrated carapace. The large, posteriorly notched plastron has a well-developed hinge between the pectoral and abdominal scutes, and the pair of meosplastral bones between the hyo- and hypoplastra are in contact on the midline. The anterior plastral lobe is relatively short, being less than twice as long as the interabdominal seam. A small axillary scute is present on each bridge.

distribution

Eastern and southeastern Africa (southern Somalia to northeastern South Africa).

habitat

These turtles inhabit permanent rivers and lakes.

behavior

These turtles are most commonly seen basking on rocks, logs, or the shoreline. They inhabit permanent water, thus they apparently do not estivate. They are frequently eaten by the Nile crocodile.

feeding ecology and diet

This species is primarily carnivorous, feeding on earthworms, snails, insects, ticks (from the hides of wallowing ungulates), fish, frogs, and carrion. They also occasionally feed on aquatic plants, as well as fruits that fall into the water.

reproductive biology

Very little is known about the natural history of this species. Females apparently nest during the summer, from at least October through January, and perhaps until April. Nests are dug by the female as far as 1,640 ft (500 m) from the water, and seven to 30 eggs, averaging 1.7 by 1 in (43 by 25 mm) and 0.7 oz (20 g), are laid in a clutch. Incubation takes only 48 days at 32–91.4°F (33°C). Hatchlings are most commonly seen after emergence in March and April.

conservation status

This species is not listed internationally for protection; but the actual status has not been formally surveyed.

significance to humans

These turtles are occasionally eaten by humans.

East African black mud turtle

Pelusios subniger

taxonomy

Testudo subnigra Lacepède, 1788, no type locality [restricted to Tamatave, Madagascar]. Two subspecies are recognized.

other common names

English: Pan hinged terrapin, pan terrapin; Afrikaans: Panwaterskilpad.

physical characteristics

East African black mud turtles are small turtles, with a maximum shell length of 7.9 in (20 cm), and an elongate, oval, unkeeled, unserrated carapace. The medium-sized plastron is posteriorly notched, has a well-developed hinge between the pectoral and abdominal scutes, and the pair of meosplastral bones between the hyo- and hypoplastra are in contact on the midline. The anterior plastral lobe is much broader than the posterior lobe, and it is only slightly longer than the interabdominal seam. The plastron is strongly constricted at the level of the abdominal-femoral seam. Axillary scutes are not present on the bridges.

distribution

Eastern and southeastern Africa (Tanzania to South Africa), Madagascar, and the Seychelles Islands.

habitat

These turtles inhabit nearly any freshwater aquatic habitat, from permanent lakes and rivers to streams, marshes, swamps, and even temporary pools.

behavior

These turtles are reported to be nocturnal, but they are known to bask at the water's edge and to migrate overland between bodies of water. They are also known to estivate underground until favorable conditions return.

feeding ecology and diet

This species is primarily carnivorous, eating worms, mollusks, insects, crustaceans, fish, amphibians, and carrion. They also occasionally consume aquatic plants, as well as ripe fruit that has fallen into the water.

reproductive biology

Little is known about the biology of this species. Courtship has not been described. One captive female laid eggs in February and March, but nesting in nature probably occurs during the summer (December and January). Clutch size ranges from eight to 12 eggs, which are elliptical, leathery, and average 1.4 by 0.8 in (36 by 21 mm). Incubation in the laboratory at 86°F (30°C) lasted 58 days.

conservation status

Not threatened, but the actual status in nature has not been formally surveyed.

significance to humans

These turtles are occasionally eaten by humans.

Resources

Books

Boycott, R. C., and O. Bourquin. The Southern African Tortoise Book: A Guide to Southern African Tortoises, Terrapins and Turtles. Privately published, KwaZulu-Natal, South Africa, 2000.

Branch, B. Field Guide to the Snakes and Other Reptiles of Southern Africa. Cape Town: Struik Publishers, 1998.

Spawls, S., K. Howell, R. Drewes, and J. Ashe. A Field Guide to the Reptiles of East Africa. San Diego: Academic Press, 2002.