Geotria

The family Geotriidae is most closely related to the lamprey family Mordaciidae, which has a similar Gondwanan distribution, and both families diverged during the Early Cretaceous. Together, their common ancestor diverged from the Petromyzontidae during the Middle Jurassic.

G. australis spawns in Pacific-draining river basins in on either side of the southern Pacific (both Australasia and Chile), while G. macrostoma spawns in Atlantic-draining basins in southern South America and nearby subantarctic islands. Despite the occurrence of both species in South America and both formerly being considered conspecific, phylogenetic studies suggest that the lineages of both species diverged during the Late Cretaceous, indicating very ancient origins for both.