(Lacepède, 1788)
African helmeted turtle
Recognition
The brown to olive carapace is oval, broad, and rather flattened dorsally; most individuals are under 20 cm in carapace length, but Loveridge (1941) recorded a South African male 32.5 cm long. The carapace may be smooth or slightly serrated posteriorly, and may have a slight keel on the 2nd to 4th vertebrals. Vertebral 1 is broader than long and the largest of the five; the 4th is also broader than long. No cervical scute is present. The plastron is usually yellow to cream colored, but may be brownish or have dark seams. It is broadest anteriorly but narrows and is deeply notched posteriorly. No hinge is present. A large plastral fenestra remains open until adulthood in the southern race P. s. subrufa, but closed by adulthood in the northern subspecies P. s. olivacea. The plastral formula is usually: hum > fem > intergul > an > abd > gul > pect. The yellow to brown bridge is well-developed, but somewhat narrow. On it are small wedge-shaped mesoplastral bones between the hyo- and hypoplastral bones. Ventrally, the marginal scutes are usually plain yellow, but in one race dark triangles are present along the seams. The skull lacks a supratemporal roof, and the quadratojugal is widely separated from the parietal. Dentary bones are not fused at the symphysis. A very small, almost indistinguishable ridge occurs on the median alveolar surface of the upper jaw. The snout protrudes. The head is brown to olive dorsally, and dark or light mottlings may be present. Laterally it becomes yellow to cream colored at the level of the dorsal edge of the tympanum. Ventrally it is unicolored yellow to cream, and two yellow barbels are present on the chin. Dorsally there are two supraorbital scales separated by a longitudinal seam. These are followed by a large frontal scale laterally bordered by two temporal scales. Neck, limbs, and tail are gray brown to olive dorsally or anteriorly, but yellowish ventrally or posteriorly. The webbed toes are composed of only two phalanges.
Stock (1972), Kiester and Childress (in Gorman, 1973), and Killebrew (1975a) reported a karyotype of 2n = 34 for Pelomedusa, but Bull and Legler (1980) reported it as 2n = 36 with 5 pairs of macrochromosomes and 13 pairs of microchromosomes.
Adult males have concave plastra with a narrower posterior lobe, and long, thick tails. Females have somewhat broader carapaces, flat plastra, and short tails. Rödel and Grabow (1995) observed males from Ivory Coast with red-spotted, nearly white heads, which they suggested might be breeding coloration.
Distribution
Pelomedusa subrufa inhabits subtropical and tropical Africa from Ethiopia, southern Saudi-Arabia and Yemen, and the Sudan westward to Ghana, Senegal, Mali, Nigeria, and the Cameroons, and southward to Cape Provinces of South Africa. It is also known from many localities on Madagascar.
Geographic Variation
Currently three subspecies have been described. The nominate race, Pelomedusa subrufa subrufa (Lacepède, 1788), the common African helmeted turtle, has its pectoral scutes meeting at the midline of the plastron. It occurs from Somalia and the Sudan west to Ghana and southward to the Cape of Africa and on Madagascar. The North African helmeted turtle P. s. olivacea (Schweigger, 1812) is a more northern race, ranging from Ethiopia and the Sudan westward to Senegal, Ivory Coast, Nigeria and Cameroon; it also occurs in Saudi Arabia and Yemen. Its pectoral scutes are widely separated. The black helmeted turtle P. s. nigra Gray, 1863c is found only in South Africa, from Kwazulu-Natal, Free State and Eastern Cape to the line joining Kuruman, Kimberley, Graaf Reinet, and Grahamstown (Bour, 1986). Its pectoral scutes meet at the midline of the black to dark-brown plastron, and it has dark triangles on the ventral surface of the marginals and dark dashes on the dorsal surface of the head. Wide zones of intergradation occur where the races meet.
P. s. olivacea and P. s. nigra were resurrected based on a low number of characters. Gasperetti (in Gasperetti et al., 1993) investigated a large series of museum types and concluded that these characters are not consistent throughout the range. Perhaps it is best to consider Pelomedusa subrufa a variable monotypic species at present, pending re-evaluation of the diagnostic features of the currently recognized subspecies.
Habitat
The helmeted turtle is semi-aquatic, living in temporary marshes, creeks, and rain holes in the open country of Africa, generally south of the Sahara Desert. It is seldom found in heavily forested areas, but is known to occur from the coastal plain to upland savannahs of 3100 m elevation. Large populations sometimes inhabit the rain pools used as watering holes by African ungulates. The habitat requirements of Pelomedusa are apparently too dry for Pelusios, and for this reason Wood (1973) feels Pelomedusa has not been preserved as fossils as often as Pelusios, which inhabits permanent water bodies. When the temporary pools dry up, Pelomedusa buries itself in the mud bottoms until the next rainy season. Loveridge (1941) reported that South African individuals may hibernate out of water in soft soil or beneath leaves from May to August.
Natural History
Courtship and mating occur in the spring. The male pursues the female with extended head and neck, often touching her hindquarters and vent with his snout. If she is nonreceptive, the male often snaps at her tail and hindlimbs. He then mounts her carapace from the rear and hooks the claws of all four feet under her marginals. His head and neck are then extended forward and downward and he sways these back and forth in front of her face while expelling a stream of water through his nostrils (Ernst, 1981a). Eventually coitus is achieved.
Nesting occurs in late spring or early summer. Nests are flask shaped and about 10-17 cm deep. At Comoé National Park, Ivory Coast, Rödel (1997) observed female P. s. olivacea migrate at least a kilometer from their nearest habitats to nest beside a plateau, where the eggs were deposited in very rocky places; the hatchlings had to climb up several meters of rock to some small pools of water where food was severely limited.
Apparently only one clutch of up to 42 eggs (Jaques, 1966; Pritchard, 1979) is laid each season; however, the normal clutch seems to be about 13-16 eggs. The white elongated (38 x 22 mm) eggs have a membranous shell and are covered with slime when laid. Hatchlings occur in 75-90 days; they are olive to black, with 25-30 mm carapaces.
Pelomedusa is carnivorous, feeding on a variety of insects, earthworms, crustaceans, snails, fish, amphibians, small reptiles, birds, and mammals. It seizes prey in its mouth and then uses the forefoot claws to tear it into shreds. Where population densities are high, several turtles may attack larger prey such as a small aquatic bird in consort, drag it underwater, and tear it apart while alive. They also feed on carrion. Rochat et al. (1962) have reported that they may act as cleaners and pick off ectoparasites from the hides of rhinoceroses that enter their water holes.
Basking is common in subtropical wild individuals, but apparently the sun is too hot for them to bask in the more tropical parts of their range. During the rainy season they wander from rain pool to rain pool, thus becoming widely distributed.
According to Loveridge (1941), when first captured, helmeted turtles emit an offensive musky odor from glands opening opposite the 4th and 8th marginals; however, they soon tame and become excellent pets.
Remark
Several authors (King and Burke, 1989; Iverson, 1992) have suggested that the original publication by Lacepède was made unavailable by the International Commission of Zoological Nomenclature in 1987. Instead, this species was attributed to Bonnaterre (1789). However, Bour et al. (1995) have presented evidence that the first volume of Lacepède's work still is available.
IUCN Red List Status (1996)
Not listed.