The giant South American turtle nests during the low water season, laying from 75 to 125 leathery eggs per clutch. Large groups of females return to the same sandy riverbanks and sandbars every year to nest in groups that are thought to decrease loss of eggs to predators due to the sheer numbers present (7). The eggs take from 42 to 47 days to hatch (3), timed to avoid the rising of the rivers which will drown any unhatched turtles (7). As with most turtles, the sex of the hatchlings is determined by the average temperature at which they are incubated; females develop at higher temperatures and males develop at lower temperatures (3).
This species is mainly herbivorous, feeding on aquatic vegetation and plant matter that falls into the water. However, it is also known to be somewhat opportunistic, feeding on small, slow-moving prey and carrion (3).
Mutual cleaning behaviour between individuals of this species has been observed. One turtle will position itself at right angles to a second turtle and use its jaws to pull algae from its shell. The turtles will then switch position (2).