Osteolaeminae was named by Christopher Brochu in 2003 as a subfamily of Crocodylidae separate from Crocodylinae, and is cladistically defined as Osteolaemus tetraspis (the Dwarf crocodile) and all crocodylians more closely related to it than to Crocodylus niloticus (the Nile crocodile).

[2][3] This is a stem-based definition, and is the sister taxon to Crocodylinae.

Osteolaeminae contains the two extant genera Osteolaemus and Mecistops, along with several extinct genera, although the number of extant species within Osteolaeminae is currently in question.

[4] The cladogram below is based on two studies that combined morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data.

[5][6] Mecistops cataphractus West African slender-snouted crocodile Euthecodon† Brochuchus† Rimasuchus† Osteolaemus osborni Osborn’s dwarf crocodile Osteolaemus tetraspis Dwarf crocodile Voay† Crocodylus anthropophagus† Crocodylus thorbjarnarsoni† Crocodylus palaeindicus† Crocodylus Tirari Desert† Crocodylus johnstoni Freshwater crocodile Crocodylus novaeguineae New Guinea crocodile Crocodylus mindorensis Philippine crocodile Crocodylus porosus Saltwater crocodile Crocodylus siamensis Siamese crocodile Crocodylus palustris Mugger crocodile Crocodylus checchiai† Crocodylus falconensis† Crocodylus suchus West African crocodile Crocodylus niloticus Nile crocodile Crocodylus moreletii Morelet's crocodile Crocodylus rhombifer Cuban crocodile Crocodylus intermedius Orinoco crocodile Crocodylus acutus American crocodile Alternatively, other morphological studies have recovered Mecistops as a basal member of Crocodylinae, more closely related to Crocodylus than to Osteolaemus and the other members of Osteolaeminae,[3][7] as shown in the cladogram below.