Dwarf crocodiles across West and Central Africa look much alike: short blunt snout, heavy body armour, adult length usually under two metres. That similarity kept them classified as one species, Osteolaemus tetraspis, described by Cope in 1861, for most of the twentieth century.
Molecular sampling published in the late 2000s found three well-separated lineages, corresponding to the Congo basin, the Ogooué basin of Gabon and Cameroon, and the Upper Guinean forests of West Africa. Estimated divergence times run to millions of years, comparable to or greater than gaps between other accepted crocodilian species. The West African lineage was matched to Osteolaemus afzelii, a name Lilljeborg published in 1867 for a Sierra Leone specimen and long treated as a synonym; the Congo lineage took Schmidt's 1919 name, osborni.
The practical effect is that each lineage now needs its own conservation accounting, in a region where forest cover and bushmeat pressure differ sharply. None of the split lineages has been separately assessed by the IUCN, some checklists still recognise only two Osteolaemus species, and how the third, Ogooué lineage should be named is not fully settled.