Big-headed Amazon river turtle
The oval carapace (to 44 cm) is domed rather than flattened and has a medial keel and smooth posterior rim. The keel is most pronounced in juveniles, but becomes lower with age, and may be absent from very large individuals. Vertebrals are usually broader than long in adults, and the 5th is posteriorly flared. A cervical scute is normally present. The flared posterior marginals may be slightly raised over the tail. Carapacial scutes of young adults contain growth annuli and rugose striae, but scutes of older turtles are often worn smooth. The carapace is gray to olive, brown, or nearly black. The plastron is large, but does not cover the entire carapacial opening. Its anterior lobe is rounded in front and broader than the posterior lobe, which is not strongly tapered to the rear but is notched posteriorly. The broad bridge is at least equal to the width of the posterior lobe. The intergular scute is longer than the gulars, which it separates. The usual plastral formula is: fem > abd > intergul > an > pect >< hum > gul. Plastron and bridge are yellow to brown. The large head is decidedly triangular in shape when viewed from above, and has a protruding snout and a strongly hooked upper jaw. Only a single weak ridge develops on the triturating surface of the maxilla. In the skull, the quadrate usually touches the jugal, but the quadratojugal extends to the parietal and separates the postorbital and squamosal bones. Premaxillae extend backward to the choanal rim, usually separating the maxillae. The incisive foramen lies completely within the premaxilla. No vomer is present. The forehead is not grooved between the eyes, but is more or less convex. The interparietal is large and expanded posteriorly, widely separating the parietals. The tympanum is as large as or larger than the breadth of the orbit. Only a single chin barbel is present. The head is usually gray to olive, but the tympanic area may be lighter in color, and in old adults the head may become noticeably white. Jaws are tan, neck and limbs gray to olive. Three large scales occur on the posterior border of the hind foot; all toes are webbed.
The karyotype is 2n = 26: 8 large to medium-sized metacentric and submetacentric chromosomes, 18 small to very small metacentric and submetacentric chromosomes (Ayres et al., 1969; Rhodin et al., 1978).
Males have longer, thicker tails than do females.
Peltocephalus dumerilianus occurs in the Amazon watershed from northeastern Peru, eastern Colombia, eastern Ecuador, and western Venezuela eastward to the mouth of the great river. It also lives in the Orinoco drainage of Colombia, where William W. Lamar has taken it from the Rios Vichada, Tuparro, Tomo, Elivita, and Muco.
This is a riverine species living predominantly in blackwater streams, but also in whitewaters, and adjacent flood-plain lagoons, oxbows, and swamps.
William W. Lamar has informed us that in the Orinoco drainage of Colombia, Peltocephalus dumerilianus nests in the dry season beginning in mid-December; Vogt et al. (1994) studied egg and hatchling development from nests marked in August and September in Pará, Brazil. The flask-shaped nests are 12-24 cm deep (Vogt et al., 1994), and are dug in floodplain forests.
Clutch size is 7 to 25. The large ellipsoidal eggs measure 50.2-59.0 x 34.0-45.8 mm, and incubation lasts at least 100 days (Medem, 1983b; Vogt et al., 1994). Hatchlings have dark-brown to gray or black carapaces (56.1 ± 2.7 mm), yellow plastra mottled with black, and several yellow spots on the sides of the brown to dark gray or black head; they weigh 32.6 ± 2.2 g (Medem, 1983b; Vogt et al., 1994).
P. dumerilianus is omnivorous, feeding on fish, invertebrates, fruits and seeds (especially palm fruits), aquatic plants, and algae (Peréz-Emán and Paolillo, 1997). Medem (1983b) reported that hatchlings will feed on fish and vegetable matter.
IUCN Red List Status (1996)