Slender-snouted crocodiles across Africa were treated as one species for most of the twentieth century. Work published in 2018 combined molecular data with morphological analysis of museum skulls collected over more than a century, and found consistent separation between populations west and east of the Cameroon Volcanic Line, which forms a long-standing barrier between the Upper Guinean and Congolian forest blocks.
The Central African lineage was assigned the name Mecistops leptorhynchus, proposed in 1835 and long treated as a synonym. Divergence between the two lineages is estimated in the millions of years, considerably deeper than many recognised crocodilian species pairs.
The practical consequence was for conservation accounting: what had looked like one moderately widespread species became one Critically Endangered species and one that is more widespread but poorly surveyed. The Central African form has not yet been separately assessed by the IUCN, and its abundance across the Congo basin is not well known.