Osteolaemus tetraspis is the smallest African crocodilian, rarely exceeding about 1.9 metres. Its short, blunt snout and heavy ossification, including well-developed osteoderms on the back and belly, make it look armoured out of proportion to its size.
It is strongly nocturnal and unusually terrestrial for a crocodilian. Individuals emerge after dark and forage along the forest floor and shallow streams, with crabs forming a large share of the diet in several studied populations, alongside frogs, fish and insects. During the day the animals occupy burrows in stream banks and cavities under root systems; burrows in Gabon have been recorded well back from open water, and some populations use flooded cave systems.
A population living in caves in Gabon shows orange-tinged skin, and its status has drawn attention, though whether the colouration reflects a distinct lineage or simply prolonged exposure to alkaline bat guano is not settled. Hunting for bushmeat is the main pressure across the range.