The skull roof, palate, and lingual side of the lower jaw of the primitive dipnoan Melanognathus canadensis are described. Melanognathus is a denticulated dipnoan with: a sarcopterygian-like composition of bones arranged in sequence on the external side of the lower jaw; “splenial” and “postsplenial” fused; plow-shaped parasphenoid; and a primitive snout region formed by a mosaic of bones. It is the sister taxon of Uranolophus, both being the most primitive dipnoans in a resolved cladogram of Devonian dipnoans. The first resolved cladogram of Devonian dipnoans shows that denticulation is the primitive feature of dipnoans, it reoccurs independently as a neotenic feature in the Late Devonian (Barwickia to Jarvikia) and also in Carboniferous/Permian (Conchopoma) dipnoans. True dipnoan tooth plates appear with Stomiahykus in the dipnoan phylogeny above Dipnorhynchus. ‘Dipnorhynchus’ lehmanni does not cluster with ‘Speonesydrion’ iani, which is part of the genus Dipnorhynchus. A new genus, Westollrhynchus, has been erected for ‘Dipnorhynchus’ lehmanni. Dipterus appears just above the node with the highest number of changes in Devonian dipnoan phylogeny.