PHYLOGENETICS WITHIN BELLEROPHON: BREAKING DOWN A CLASSIC WASTEBASKET TAXON

The genus Bellerophon (de Montfort 1808) typifies an extinct group of Paleozoic marine gastropods, the Bellerophontina. Bellerophon is currently assigned over 150 species in the Paleobiology Database, and is likely a “wastebasket” taxon. Analyzing these taxa at the species level is thus important not only to improve taxonomy, but also to uncover origination and extinction dynamics, and trends in morphologic evolution. These planispiral coiled snails are found in both carbonate and siliciclastic rocks, resulting in a variety of preservational modes that must be accommodated when scoring character states. Published images as well as specimens selected from invertebrate paleontology collections were used to examine 41 taxa, which were coded for 137 states among 64 characters. Several of these are continuous morphometric characters that are treated as “ordered” series and weighted by 1/(n-1), where ‘n’ designates the number of character states. Shell characters in conjunction with stratigraphic data were analyzed using stratocladistics, with stratigraphic bins of 5 million years each. Aglaoglyptia, Pharkidontus, and Mogulia were used as outgroups in the phylogenetic analysis. As expected given its taxonomic history, Bellerophon was found to be a paraphyletic relative to several other genera in Bellerophontidae. In some cases, these other genera may be monophyletic groups (e.g. Aglaoglyptia). However, the outgroup Pharkidontus appears to be polyphyletic, suggesting the features linking Pharkidontus and Bellerophon are convergent. Among species assigned to Bellerophon, multiple clades were recovered that should be considered for classification as unique genera. In particular, the oldest clade from the Carboniferous displays a distinct loss of filling around the coiling axis, while maintaining a sharp sinus. This is unique from the majority of Bellerophon species, which shows filling around the coiling axis in addition to a sharp sinus. Additionally, features such as columella thickness and orientation, as well as tighter coiling, were important in differentiating species within Bellerophon. These characteristics are easily recognizable even on incomplete specimens making them excellent diagnostic tools within this genus.