Females nest on sandbanks during the dry season. The embryos develop to term and then enter an arrested state rather than emerging on schedule. Hatching is triggered when the rising wet-season river inundates the nest, and the hypoxia that follows submergence appears to be the immediate cue.
The timing matters twice. Emerging into a dry sandbank would strand hatchlings far from water, and synchronised emergence across a clutch swamps predators waiting at the bank. Clutches can be induced to hatch early in captivity simply by immersing the eggs.
The adults are unusual in a second way. Every other freshwater turtle has webbed, clawed feet; the pig-nosed turtle has flippers built like a sea turtle's, an independent solution to the same problem of moving through open water. The fleshy snout works as a snorkel and carries touch receptors used to find food in murky river bottoms.