Ogilby, 1890
Northern Australian snake-necked turtle
Recognition
This is a large Chelodina reaching a carapace length of at least 35 cm; Cogger (1975) reported the maximum length to be 40 cm. The carapace is oval, somewhat elongated, and usually is broadest behind the middle. Its surface is covered with small rugosities. The posterior carapacial rim is smooth to slightly serrated, and there is no medial vertebral keel or depressed groove in adults. All vertebrals are broader than long in adults, although the 2nd is almost as long as broad. The 1st is the largest and is flared anteriorly, the 4th is the shortest, and the 5th is flared posteriorly. No neurals are present. The carapace is brown to black and the seams may be darkly outlined. Some individuals have lighter brown or yellowish pigment on the dorsal surface of the marginals. The plastron is moderate, but does not cover the entire carapacial opening. Its forelobe is broad and tapers to a rounded front; the hindlobe is broad across the femorals but tapers to the rear and is deeply notched posteriorly. The plastral formula is: intergul > pect > abd > fem > an > hum > gul. The intergular is almost twice as broad as long, and may extend anteriorly to separate the gulars. Surfaces of the plastron and narrow bridge are covered with rugosities, and the undersides of the marginals, plastron, and bridge are yellow with dark seams. The large head is broad and flat, the snout does not protrude, and the upper jaw is neither notched nor cusped. Chin barbels are present but variable in number. The neck is very long and thick, over 75% as long as the carapace. The dorsal surface of the head is covered with irregularly shaped scales and that of the neck with small blunt tubercles. Head and neck are olive, brown, or gray; the jaws may be cream colored. Limbs and tail are gray. A series of large transverse scales occur on the anterior surface of the forelimbs.
There are 54 chromosomes in the karyotype (Bull and Legler, 1980).
Males have much longer, thicker tails than do females.
Distribution
Chelodina rugosa occurs only in northern Australia, where it is known from the Cape York Peninsula westward to the Kimberley District of Western Australia (Cogger, 1975).
Geographic Variation
The species is little known and poorly described. In the past it has been confused with both Chelodina oblonga and C. siebenrocki, and in fact it may be synonymous with C. siebenrocki; additional study of this relationship is badly needed.
Two undescribed species cf. C. rugosa are discussed under Genus Chelodina.
Habitat
Cogger (1975) reported the habitat as swamps, billabongs, waterholes, and slow-flowing rivers.
Natural History
Cann (1978) reported that nesting occurs in March and that a 29 cm female deposited a clutch of 14 elongated (35 x 25 mm) eggs. Nests are excavated in soft substrate under shallow water in the littoral zone of seasonally flooded swamps during the wet and early dry season (Kennett et al., 1993b). Embryonic development is arrested until water levels drop in the following dry season and oxygen enters the nest through the drying mud (Kennett et al., 1993a; Kennett, 1996). Hatchling emergence probably coincides with heavy rain or flooding at the beginning of the next wet season, when rains have softened the ground.
Chelodina rugosa is an obligate carnivore, feeding primarily on fish, fast moving aquatic invertebrates and carrion. Kennett and Tory (1996) found aquatic insects in 65.5% and aquatic vertebrates in 75.8% (fish in 71.3%) of the turtles they examined, and listed the following prey: insects, shrimp, nematodes, leeches, snails, conchs, fish and frogs.
Living in a wet-dry seasonal habitat, C. rugosa is almost exclusively active in the wet period, and aestivates over the 4-5 month dry period. Metabolism is suppressed during aestivation (Kennett and Christian, 1994).
Remark
Wells and Wellington (1985) split C. rugosa into Macrochelodina rugosa (Cape York, Queensland) and M. billabong (Northern Territory), but without diagnosis.
IUCN Red List Status (1996)
Not listed.