Lower Carboniferous conodonts of similar morphological form occur at different horizons; they are interpreted as functional homeomorphs. There is a phylogenetic relationship between the following pairs of genera: Spathognathodus and Pseudopolygnathus, Polygnathus and Siphonodella, Polygnathus and Cavusgnathus, Spathognathodus and Gnathodus, Spathognathodus and Bactrognathus, Bactrognathus and Scaliognathus. The evolution of the genera Patrognathus, Clydagnathus, Taphrognathus, and Cavusgnathus is closely related and shows examples of homeomorphy.
A detailed study of the genus Gnathodus reveals the presence of populations with growth stages of different individuals. The evolution of gnathodid populations shows the presence of homeomorphic members of ontogenetic stages, which are also interpreted as having a functional significance.