(Freiberg, 1945)
Chaco side-necked turtle
Recognition
This species is a medium-sized (17.5 cm) Argentine side-neck with several enlarged pointed tubercles on its upper thighs. Its elliptical adult carapace appears flattened because of a shallow dorsal groove running between the posterior part of the 1st vertebral and the anterior part of the 5th vertebral. Vertebrals 1-3 are broader than long, the 4th is narrower than long in adults (broader than long in juveniles), and the 5th is equal in length and breadth or only slightly longer than broad. Marginals are not serrated, and the anterior- and posteriormost are broadest while those lateral are narrow and upturned. Posterior marginals are depressed over the thighs. The carapace is highest just behind the center and broadest at the level of the 8th marginals. It varies from yellow brown to gray brown or olive, often with dark seam borders. Plastron and bridge are yellow with a broad, dark seam-following pattern. In some, the dark pigment may become so extensive that the yellow is restricted to the outer edges of the scutes. Mertens (1954b) speculated that this dark pigmentation fades with age. The intergular scute is approximately half as long as the length of the plastral forelobe. The plastral formula is: intergul > fem > abd >< an > gul > hum > pect. The plastral forelobe is broader than the hindlobe, which contains a wide posterior notch. The head has a wide, yellowish medial stripe bordered on each side by a gray-brown lateral stripe. Its tympanum is yellow, and its dorsal surface is covered with large scales. The iris is white. The neck is gray brown dorsally, blending into grayish yellow ventrally. Its dorsal and lateral surfaces contains large conical tubercles. The yellow legs are covered with large scales and the toes are webbed. On the inside of each thigh, near the tail, is a series of enlarged conical tubercles, at least one of which is larger than the rest.
Males have concave plastra, longer, thicker tails, and better developed thigh spines than do females.
Distribution
Acanthochelys pallidipectoris ranges from the Chaco region of Argentina to Paraguay; it probably also occurs in eastern Bolivia.
Habitat
This species usually frequents rivers, ponds, lagoons, and other slow-moving, shallow water bodies, but may venture onto land for short periods.
Natural History
Courtship between captives was described by Horne (1993). Courtship behavior began in early September and continued sporadically until late November. The male approached the female from the rear with his head and neck extended across the length of the her carapace. He then rubbed his head and neck back and on her carapace, while trying to maneuver the female into a position where he could more easily mount. When mounted, he grasped the rim of her carapace with all four feet and began prodding her head and neck with his face, until she folded them beneath her carapace, making her vent more accessible. Courtship bouts averaged 30 minutes (15-90).
Oviposition first occurred on 18 November, when one egg was laid in the water. Two weeks later a second egg was also deposited in the water, and on 9 March a third egg was found in the water. Courtship began again the next fall, and on 16 December two eggs were laid after oxytocin was administered.
The hard-shelled eggs from the two clutches were 25-28 mm long by 22-24 mm wide. Iverson (in Horne, 1993) reported a clutch of four eggs, and Richard (1991) reported a 26 September clutch of five pinkish-white 24.4-25.5 x 23.6-24.1 mm eggs.
Captives kept by Horne (1993) ate live fish, beef, poultry, newborn mice, tadpoles (Hyla), and mealworm larvae. In the wild, this species is said to feed on fish and larval amphibians (Cei, 1993).
IUCN Red List Status (1996)
Vulnerable (A1c, D1).