(Schweigger, 1814)
Geoffroy's side-necked turtle
Recognition
The oval, flattened carapace (to 35 cm) is broadest behind the center and has a smooth posterior rim (there may be a slight supracaudal notch). A slight medial groove is present on the depressed dorsal surface in adults, and a weak medial keel may be present on younger individuals. The flared 1st vertebral scute is largest and broader than long; the 2nd through 4th are broader than long in juveniles, but lengthen with age until they may be longer than broad in adults; the 5th is also broader than long and flared. The cervical scute is usually long and narrow. The carapace is brown to black with gray mottlings and has a yellow border; its scutes are often rugose with raised striations. The plastron is well-developed and has an anal notch. Its forelobe is only slightly broader than the hindlobe, and the bridge is relatively broad. The variable plastral formula is: fem >< intergul > an >< abd > pect >< gul >< hum; the intergular completely separates the gulars. In older adults, the undersides of the marginals, bridge, and plastron may be uniformly yellow to light brown; juveniles and young adults have an extensive red and black plastral pattern. The large, broad head has a projecting snout, an upper jaw lacking a notch or hook, and two yellow chin barbels. Dorsally, the head is covered with small, irregularly shaped scales. It is gray to olive dorsally, often with black vermiculations; a broad black stripe runs backward on each side from the nostril through or over the orbit and tympanum to the side of the neck, and a second black stripe runs along the upper jaw to the side of the neck; between these stripes is a yellow or cream-colored band. On the yellow chin and underside of the throat is a series of black streaks or stripes. The jaws are yellow. The neck may contain some blunt tubercles. Limbs are gray to olive on the outside, but have cream-colored areas beneath; soles and palms of the feet may be black.
Males have longer, thicker tails and shallowly concave plastra.
Distribution
Phrynops geoffroanus ranges from southwestern Venezuela, southeastern Colombia, eastern Ecuador, and eastern Peru, southward and eastward through southwestern Brazil and northern Bolivia to Paraguay and northeastern Argentina, then northward through eastern Brazil. It also occurs in eastern Venezuela, and in adjacent Guyana. Its presence in the central Amazon basin is unknown.
Geographic Variation
Two subspecies are recognized. Geoffroy's side-necked turtle, Phrynops geoffroanus geoffroanus (Schweigger, 1814), occurs in central and southern Brazil, Paraguay, northeastern Argentina, and Uruguay. It has only a medial vertebral keel, and its intergular scute is shorter than its distance from the abdominal scute. P. g. tuberosus (Peters, 1870), Peters' side-necked turtle, occurs in the Guianas and eastern Brazil southward to Bahia. A population of this subspecies also occurs in Colombia, but Pritchard (1979) feels it may represent a different subspecies. P. g. tuberosus has a medial vertebral keel flanked on each side by a lateral keel formed by a series of raised knobs along the dorsal surface of each pleural scute, and its intergular is usually longer than its distance from the abdominal. Lamar and Medem (1982) have noted that those Colombian turtles referred to this race differ considerably from the nominate form. Their status needs clarification. The southernmost populations of P. geoffroanus have been designated as a separate species, P. williamsi Rhodin and Mittermeier, 1983.
Habitat
This side-neck frequents rivers, lakes, and lagoons with slow current, soft bottoms, and abundant aquatic vegetation.
Natural History
De Barros Molina (1996) observed courtship and mating behavior in captives in Sao Paulo, Brazil. Courtship behavior took place in water from late October to mid-April, and consisted of four phases. The first phase involved searching for the female, when the male approached another turtle from the rear and smelled its cloacal vent and bit at its tail and posterior carapacial rim (if such behavior was directed toward a male, aggressive action was stimulated). Usually females tried to avoid males, starting phase 2, the pursuit. During the pursuit, both turtles moved quickly through the water or over the bottom, and often changed directions. To avoid pursuit, females sometimes left the water. Once the female stopped retreating from the male, the third phase, precopulation, occurred. The male grasped the female's carapace with all four feet, holding the marginals with his claws. His neck and head were fully extended, and with lateral movements he rubbed his chin over the dorsal surface of her head. Sometimes the forefeet were shifted forward to rub against the female's head while his position was anchored with the hind feet. Occasionally he lowered his head and rubbed his chin against her nostrils. The female's neck and, less often, forelegs were bitten (sometimes at this point a second male would bite the tail of the mounted male). The female usually remained motionless during this precopulation phase. Phase 4 consisted of copulation when the male repositioned himself, brought his tail under that of the female, and inserted his penis. Prior to insertion, the male moved rearward on the female's carapace. The male continued to bite the female's neck during copulation, and the actual mating took 10-30 minutes. Total duration of the four phases of courtship and mating took 15-50 minutes.
The nesting season extended from January to March in De Barros Molina's (1996) Brazilian captives. In Colombia, the nests are dug from December to February, and in Venezuela in March and April (Pritchard and Trebbau, 1984).
The eggs are almost spherical (26-34 x 22-32 mm) and are laid in clutches of 10 to 20 (Pritchard and Trebbau, 1984; Wicker, 1984). In captivity, up to 5 clutches may be produced per season; incubation takes 4 to 4.5 months at 28-30°C (Wicker, 1984).
Hatchlings have carapace lengths of 32-42 mm (Wicker, 1984). Their carapaces are rugose with a slight vertebral keel and a slightly serrated posterior rim; the undersides of the marginals, bridge, and plastron are pinkish red with a pattern of irregular black marks.
The food consists mostly of fishes, aquatic insects, and other small aquatic invertebrates; these turtles do well in captivity on fish and chopped beef. In the wild they are often observed basking (Pritchard and Trebbau, 1984).
IUCN Red List Status (1996)
Not listed.