Red-headed river turtle
A small Podocnemis species, the carapace is only 32 cm long. The adult carapace is oval somewhat domed, broadest behind the center, and has a smooth posterior rim. There is only a weak cervical indentation. A medial keel is best developed on the 2nd or 3rd vertebrals. Vertebrals are broader than long in juveniles, but in adults the first two may be as long as broad or even longer than broad. The 4th and 5th are the smallest, and the 5th is posteriorly expanded. The carapace is brown to dark chestnut brown; there is a lighter border around the rim. The plastron is large, but does not completely cover the carapacial opening. The anterior lobe is longer but slightly narrower than the posterior lobe, which is notched posteriorly. The bridge is broad, as wide or slightly narrower than the posterior lobe. The plastral formula is: abd > pect > fem > intergul > an > gul >< hum. The intergular is long and narrow, and completely separates the gular scutes. The plastron is brownish gray along the outside but yellow, orange, pink, or red along the midseam. The bridge is brown to gray. The head is elongated with a protruding snout and a distinctly notched upper jaw. This notch continues to the nostril as a groove, and there is also an interorbital groove. Two long parallel ridges occur on the triturating surface of the maxilla. Premaxillae are short, do not extend posteriorly as far as the choanal rim, and join with the small vomer to separate the maxillae. The incisive foramen is completely within the premaxilla. The tympanum is as broad as the orbit. The interparietal scute is short and very broad, at times even heart-shaped; the parietals usually meet behind it. Suboculars are present, and there are two chin barbels. The head is dark brown to dark gray in ground color. Juveniles < 12 cm contain large red or reddish orange (rarely yellow) spots on the snout and tympanum, and a similarly colored transverse band stretches across the head from tympanum to tympanum. Adult males retain this coloration, but the brightest colors fade to dull brown in adult females. Jaws are dark and the neck and limbs gray to brown. There are usually three, rarely two, large scales on the posterior margin of the hind foot.
The karyotype is 2n = 28, with 6 large to medium-sized metacentric and submetacentrics, 4 large to medium-sized subtelocentrics, 16 small to very small metacentrics and submetacentrics and 2 small acrocentric and subtelocentric chromosomes (Ayres et al., 1969; Rhodin et al., 1978).
Males have larger, thicker tails and deeper anal notches; females have shorter tails and shallow, V-shaped anal notches.
Mittermeier and Wilson (1974) reported that Podocnemis erythrocephala occurs in the Rio Negro and Rio Casiquiare drainages of Colombia, Venezuela, and Brazil; the Casiquiare forms a link between the Rios Negro and Orinoco, and the single verified Colombian specimen is a juvenile from the mouth of the Rio Inírida of the Orinoco drainage (Lamar, 1986).
Podocnemis erythrocephala seems to prefer blackwater streams and rivers, but is also known from some whitewaters.
Nesting occurs from August to November with the peak in September and October (Mittermeier and Wilson, 1974). The eggs are usually laid in sandy, brushy areas, and probably more than one clutch is laid each season. A typical clutch includes 5 to 14 eggs (although Freiberg, 1981, reported the clutch size to be 30-40). The eggs are ellipsoidal (43.0 x 27.0 mm) with either rigid calcareous or slightly flexible shells. Hatchlings have approximately 40 mm carapaces.
Mittermeier and Wilson (1974) found this species to be primarily herbivorous, feeding on aquatic plants and fallen fruits, but it is also taken on lines baited with fish, and captives will accept fish. Rhodin et al. (1981) reported that juvenile Podocnemis erythrocephala sometimes practice an inertial feeding mechanism, termed neustophagia, for swallowing fine particulate matter from the water's surface (Belkin and Gans, 1968). This is a coordinated mechanism in which the turtle opens its jaw at the surface, keeping the cutting edge of the mandible 1-2 mm below and parallel to the surface, while rapidly expanding the hyoid and pharynx to the maximum, creating a low pressure area in the mouth and throat which sucks in only the surface water and its contents. Contraction of the jaws forces the water out while the particulate matter is filtered and retained.
IUCN Red List Status (1996)