 New Guinea crocodiles have a mostly aquatic lifestyle and are largely nocturnal . They spend much of the day underwater , often with their nostrils and eyes above the surface . Powerful side @-@ to @-@ side movements of their tails propel them through the water and they use both tail and legs to steer . When on land , they favour shady , dense areas of undergrowth . They tend to bask in a group during the day , dispersing at night to feed . 
