Dead bellerophontids walking — The short Mesozoic history of the Bellerophontoidea (Gastropoda)
The bilaterally symmetrical gastropods grouped in the extinct superfamily Bellerophontoidea are considered as a typical Early Triassic example of Dead Clade Walking. They survived the Permian–Triassic extinction but disappeared in the Early Triassic. We analysed all Triassic occurrences of bellerophontoideans known from the literature and revised their taxonomic assignment and stratigraphic occurrence. We confirm eight Early Triassic species of Bellerophontoidea representing three genera (Dicellonema, Retispira, and Warthia) from two families (Bellerophontidae and Euphemitidae). Bellerophontoideans were globally distributed in the Griesbachian, Dienerian, and Smithian (early-to-mid-Early Triassic) and at some localities they formed mass accumulations. Due to their relatively high diversity and abundance in the Early Triassic, they apparently had a good chance to recover from the Permian–Triassic extinction but finally became extinct at the Smithian/Spathian boundary. We could not confirm any bellerophontoidean occurrence from Spathian and younger strata. The end-Smithian extinction event was previously found for conodonts and ammonoids. Thus, a double phased extinction at the end-Permian and end-Smithian extinction events finally removed the important Paleozoic group Bellerophontoidea.We raise Dicellonema (which has been earlier proposed as subgenus of Bellerophon) to genus level. It is represented by two species: D. dicellonemata Yü and Wang in Yü (1975) and D. abrekensis (Kaim, 2009). Two other species that may represent nomina dubia are included only tentatively: D. panxianensis (Yü) in Wang and Xi (1980) and D. granatricarinata (Wang) in Wang and Xi (1980). Two other species are transferred from Bellerophon to Warthia: Warthia vaceki (Bittner, 1899a) and W. borealis (Spath, 1930). Euphemites guizhouensis Pan, 1982 belongs actually to Retispira and might be a synonym of R. asiatica (Wirth, 1936). We could not confirm the presence of Bellerophon (sensu stricto) and Euphemites in the Early Triassic.