Two lineages exist for Cahabagnathus. Lineage 1 is C. friendsvillensis–C. chazyensis–C. sweeti–C. carnesi. Three new species are proposed in lineage 2, which consists of C. baueri n. sp.–C. directus–C. cooperi n. sp. and C. craigi n. sp. The distribution pattern of Cahabagnathus was strongly influenced by Chazyan sea-level changes. The wide distributions of C. friendsvillensis and C. sweeti correspond to two large transgressions and the more narrow distribution of C. chazyensis and C. carnesi correspond to regression events. A similar relationship exists between sea-level change and the distribution of species in lineage 2. Evolution of the cahabagnathids was apparently influenced by the rise of sea level, which widely distributed taxa, and the fall of sea level, which isolated taxa. We propose that it was from peripheral isolates of widely distributed taxa that endemic Cahabagnathus taxa (C. baueri, C. cooperi, C. craigi, C. chazyensis, and C. carnesi) evolved.