Cornalia, 1849
Six-tubercled river turtle
Recognition
This is one of the smaller species of Podocnemis, reaching a carapace length of 31.7 cm. Its domed carapace is elliptical and broader behind the center. The posterior rim is serrated in juveniles, but only slightly so or smooth in adults; a cervical indentation may be present. A blunt medial keel is present on vertebrals 2 and 3. All vertebrals are broader than long with the 1st and 5th the smallest, and the 5th posteriorly expanded. Surfaces of the carapacial scutes are usually smooth and show few if any growth annuli. The carapace is gray to olive brown. The plastron is large but does not completely cover the carapacial opening. Its anterior lobe is rounded in front and broader than the posterior lobe. The anal scutes are decidedly tapered and much narrower than the femorals. A shallow posterior notch is present. A unique character (which gives this turtle both its scientific and common names) is the presence of six pairs of prominent swelled tubercles on the plastron of juveniles. These occur at the base of the bridge on the pectoral and abdominal scutes and at the outer posterior point of the femorals. These swellings disappear with age, although those on the pectoral scutes may persist into adulthood. The plastral formula usually is: abd > pect > fem > intergul > an > gul > hum. The long intergular separates the gulars. The bridge is not as broad as the width of the plastral posterior lobe. Both plastron and bridge are yellow to gray or brown. The broad head has a protruding snout and notched upper jaw. There is only a single weak ridge on the triturating surface of the maxilla. The premaxillae separate the maxillae and extend to the choanal rim. The incisive foramina lie completely within the premaxillae. There is no vomer. The interparietal scale is elongated and widely separates the parietals, which, although also elongated, do not touch behind the interparietal. Large subocular scales are usually present. A deep groove lies between the orbits, and the tympanum is about as broad as the orbit. One or two chin barbels are present. The head is olive to reddish brown with cream-colored jaws. The neck is dark gray to olive dorsally but lighter colored ventrally; limbs are gray to olive. Three large scales occur on the posterior margin of the hind foot.
Ayres et al. (1969) and Rhodin et al. (1978) reported the diploid chromosome number to be 28 (6 large to medium-sized metacentric and submetacentric chromosomes, 4 large to medium-sized subtelocentrics, 14 small to very small metacentrics and submetacentrics, and 4 small acrocentrics or subtelocentrics).
Males have longer, thicker tails than do females.
Distribution
Podocnemis sextuberculata occupies the Amazon drainages of northern Brazil, northeastern Peru, and southeastern Colombia.
Natural History
Vanzolini (1977) reported that in Brazil the nesting season is June and July on the Rio Purus and August and September on the Rio Trombetas, and Pritchard (1979) stated that, in the upper Amazon, nesting occurs in October on the Rio Caquetá and in November and December on the Rio Putumayo. Nesting takes place in July-October in the Reserva Nacional Pacaya-Samiria, Peru (Soini, 1996). The nests are dug in low beaches and bars of sand which are particularly vulnerable to flooding; probably two clutches are laid each season (Vanzolini, 1977).
Clutches include 7 to 22 ellipsoidal (34-44 x 24-30 mm) eggs. Hatchlings have carapace lengths of 45-47 mm, and their vertebral keel and six plastral tubercles are well-developed.
Foods in the wild include aquatic plants and fish.
IUCN Red List Status (1996)
Vulnerable (A1acd).