Historically, all Frog Pokémon have been divided into two different groups: Tadpolia and Atadpolia. One includes all species with at least one tadpole stage (not counting Baby forms), while the other includes all the species with no true tadpole stage. This division was always considered by many as fundamentally flawed, as species like Poliwrath (Poliwagus fighterus) or Politoed (Poliwagus kingii) show a tadpole that seems more developed than others like Seismitoad (Tympolus vibrationus) and Bellibolt (Tadbulbus electricus). The peculiar anatomy of Poliwag is usually used as the main reason this strict division should not be considered valid, while others use it as a connection between the two groups, while still keeping them separate (considering Poliwrath and Politoed as part of Tadpolia).

New morphological analysis on the prehistoric Frog Belzeboss (Prodpolus toxisackia), in conjunction with DNA analysis of modern species, the results of which were published by Dr. Hans Pheeb (Pheeb et al., 2024) in a new paper, place Belzeboss as a sister taxon to Seismitoad, as opposed to the previous study placing it as the ancestor to all Frog Pokémon. This has once again challenged the idea of a strict distinction between Tadpolia and Atadpolia.

Belzeboss is a very interesting species, having large sacs on their back containing poisonous substances that can be expelled through the skin as a defense mechanism against predators and opponents. This character has been connected to Toxicroak’s poison sacs, further validating the idea of some researchers that Seismitoad and Toxicroak are related, as shown in some DNA analysis. This idea is, however, very controversial at this time, and further research is needed to either confirm or deny it.