This is the largest tortoise (to 82 cm) living on the mainland of South America. It has an elongated carapace with a shallow cervical indentation, the lateral sides parallel, and posterior marginals slightly serrated. There is no cervical scute. Vertebrals are broader than long, and the 1st and 5th are laterally expanded. Well-defined growth annuli surround the slightly raised areolae of the vertebral and pleural scutes. There are usually 11 marginals on each side, and the single supracaudal is undivided and downturned. The carapace is brown with yellow to orange vertebral and pleural areolae; yellowish or orange pigment also occurs at the lower edge of each marginal. The plastron is well-developed. Its upturned forelobe tapers toward the front and is about as long as, but slightly narrower than, the hindlobe, which bears an anal notch. The plastral formula is: abd > hum > fem > gul >< pect >< an; the paired gulars are thickened, but do not extend much beyond the carapacial rim, if at all. Each gular scute is dorsally subdivided, ultimately producing four scales. The bridge is wide with a moderate-sized axillary and a smaller inguinal that barely touches the femoral scute. The plastron is yellowish brown with darker pigment along the mid- and transverse seams. The head is moderate in size with a nonprojecting snout and a slightly hooked upper jaw. Its large prefrontal scale is divided longitudinally and followed by a subdivided frontal scale; other head scales are small. Head scales are yellow to orange with dark borders; the jaws are dark brown. The anterior surface of each forelimb is covered with large yellow or orange, non- or only slightly overlapping scales. No enlarged tubercles occur on the thighs, and the tail lacks a large terminal scale.
The karyotype is 2n = 52; 28 macrochromosomes (16 metacentric or submetacentric, 12 telocentric or subtelocentric) and 24 microchromosomes, it differs from that of G. carbonaria by centromere placement of one of the smallest macrochromosomes (Bickham and Baker, 1976a, 1976b).
Males are generally larger than females, and have concave plastra; the carapace expanded over the hindlimbs; low, flattened, elongated profiles; and longer, thicker tails. Females have domed, non-expanded carapaces, flat plastra, and shorter tails.
G. denticulata ranges from southeastern Venezuela through the Caribbean lowlands of the Guianas to Brazil, where it occurs throughout the Amazon Basin to eastern Ecuador and Colombia, northeastern Peru, and northern and eastern Bolivia. It also occurs in an isolated range in eastern Brazil and on Trinidad.
This is a variable species, but no subspecies have been named. A thorough study of geographic variation would be useful.
Geochelone denticulata is a denizen of tropical evergreen and deciduous rainforests.
Mating probably occurs throughout the year. Males identify each other through characteristic head movements not made by females. The male then sniffs the cloacal region of the female, perhaps to determine if she is his species. Some pushing and ramming and biting at her limbs may follow to immobilize her before copulation, or mounting and intromission may occur immediately. Clucklike vocalization may be emitted by the male during courtship and while mounted.
Nesting probably also occurs throughout the year (it has been observed in August to February in Colombia), and it is likely several clutches are laid each year. Clutches may contain 1-20 eggs, but 4-8 eggs are more normal (Pritchard and Trebbau, 1984); eggs are elongated (40-60 x 35-44 mm) with brittle shells. Incubation takes four or five months. Hatchlings are rounded and flat (47-60 mm) and have distinct toothlike projections on the rims of the anterior marginals (hatchlings of G. carbonaria have smooth anterior rims),
Geochelone denticulata feeds on a variety of vegetative and reproductive plant parts (grasses, leaves, vines, roots, bark, fruits, flowers), fungi (gilled and woody mushrooms), animal matter (insects, snails, various vertebrate carrion), soil, sand, and pebbles (Pritchard and Trebbau, 1984; Moskovits and Bjorndal, 1990). Fruits are the dominant food in the wet season; flowers in the dry season. Other foods are consumed throughout the year. Preferred foods are highly fermentable, and have high concentrations of total minerals, nitrogen, and phosphorus, and low calcium to phosphorus ratios. Other foods eaten are abundant and have high calcium concentrations.
IUCN Red List Status (1996)