This handsome tortoise has an elongated carapace (to 51 cm) with a shallow cervical indentation, the lateral sides distinctly concave when viewed from above, and a smooth posterior rim. There is no cervical scute. Vertebrals are broader than long, and the 1st and 5th are laterally expanded. Well-defined growth annuli surround the raised vertebral and pleural areolae. There are usually 11 marginals on each side, and the single supracaudal is undivided and downturned. The carapace is black, with the vertebral and pleural areolae yellow to reddish orange; a light spot of the same color occurs at the base of each marginal. The plastron is well-developed. Its upturned forelobe tapers toward the front and is about as long and broad as the hindlobe, which bears an anal notch. The plastral formula is: abd > fem ³ hum > gul > an >< pect; the paired gulars are thickened, but do not extend much beyond the carapacial rim, if at all. The dorsal surface of each gular scute is usually not subdivided. The bridge is wide with a moderate axillary and a moderate to large inguinal which is in broad contact with the femoral scute. The plastron is yellowish brown with some dark pigment along the mid- and transverse seams. The head is moderate in size with a nonprojecting snout and a slightly hooked upper jaw. Its prefrontal scale is short and divided longitudinally, and followed by a large undivided frontal scale. Other head scales are small. Head scales are yellow, red, or orange; the jaws are dark. The anterior surface of each forelimb is covered with large, red, slightly or nonoverlapping scales. No enlarged tubercles occur on the thighs, and the tail lacks a large terminal scale.
G. carbonaria has a total of 52 chromosomes; 28 macrochromosomes (18 metacentric or submetacentric, 10 telocentric or subtelocentric) and 24 microchromosomes (Stock, 1972; Bickham and Baker, 1976a, 1976b).
Males have concave plastra, lower flattened carapaces with deep lateral concavities, and longer, thicker tails. Females have more domed, shallow, laterally concave carapaces, flat plastra, and shorter tails.
Geochelone carbonaria occurs in southeastern Panama and west of the Andes in Chocó of Colombia, but its main range is east of the Andes in eastern Colombia, Venezuela, and the Guianas to eastern Brazil, south to Rio de Janeiro, and west to eastern Bolivia, Paraguay, and northern Argentina. It seems absent from almost all but the eastern parts of the Amazon Basin. This tortoise may occur naturally on Trinidad, and has been introduced on quite a few Caribbean Islands, including St. Croix in the Virgin Islands. The recent discovery of a Pleistocene G. carbonaria on Anguilla of the northern Lesser Antilles (Lazell, 1993) may indicate a greater past distribution.
No subspecies have been described, but Pritchard and Trebbau (1984) suggested that pattern and size differences exist between various populations.
Where it is sympatric with Geochelone denticulata, G. carbonaria is more prevalent in moist savannahs (which are seldom entered by denticulata), but where denticulata does not occur, carbonaria seems to be a humid forest dweller. Perhaps there is competitive exclusion by denticulata.
Mating occurs, at least in captivity, year round. As in Geochelone denticulata, males distinguish other males from females by their responsive head movements; and, if a male, some ramming and pushing follows. If no responsive head movement is given, the male walks behind the other tortoise and sniffs its cloacal region, presumably for odors confirming it a female of the proper species. The male may then mount the female or he may ram and push to subdue her. During copulation the males utter clucking sounds.
Nesting occurs from June to September and the female digs a flasklike cavity about 20 cm deep. Two to 15 eggs are laid in one clutch, and probably several clutches are deposited each season. Eggs are elongated (40-59 x 34-48 mm) with brittle shells. Incubation takes 140-150 days (Cei, 1993); in captivity the young hatch after 117-158 days (at 29-31°C; Houtman and De la Fosse, 1989). Hatchlings are rounded and flat (39-45 mm, 22-30 g) and have no toothlike projections on the rims of the anterior marginals, as occur in hatchling G. denticulata.
Geochelone carbonaria feeds on fungi, live and dead foliage, stems, fallen fruits, flowers, soil, sand, pebbles, live snails, termites, and carrion (lizards, birds, mammals) (Pritchard and Trebbau, 1984; Moskovits and Bjorndal, 1990). Moskovits and Bjorndal (1990) reported that fruits were included in the diet all year long, but especially in the wet season; flowers were the dominant food in the dry season, and the other foods were eaten throughout the year. Typical foods are relatively abundant and have high calcium concentrations, while preferred foods have high fermentabilities, high concentrations of total minerals, nitrogen and phosphorus, and low calcium to phosphorus ratios.
IUCN Red List Status (1996)