PALEOBIOGEOGRAPHY OF SWADELINA (PENNSYLVANIAN CONODONT) AT 20 YEARS--A REVIEW AND PROSPECTS

Twenty years ago, the Upper Carboniferous (Pennsylvanian) conodont genus Swadelina Lambert, Heckel, and Barrick was erected. This genus is characterized by troughed idiognathodid P1 elements that bear a short carina and well-defined lobes or other ornamentation on the dorsal (or anterior) platform. The P2 elements were also recognized to differ subtly from those of its ancestral genus, Idiognathodus. Currently eleven species have been assigned to Swadelina, but only four are by original designation. The other seven species were previously assigned to Idiognathodus or Streptognathodus, then reassigned once Swadelina was established. Most Swadelina species have been recovered from Bashkirian and Moscovian strata in China and eastern Europe. The two original North American species are limited to latest Moscovian (latest Desmoinesian) strata on that continent.

The earliest known Swadelina species are Sw. einori (Nemirovskaya and Alekseev) and Sw. subdelicata (Wang and Qi), which have both been recovered from the middle Bashkirian of Guizhou Province. Swadelina species are first recovered in the Donets and Moscow basins from late Bashkirian strata. These biostratigraphic relationships suggest that Swadelina evolved in South China, then dispersed across the northern Paleotethys Ocean, and eventually through the Uralian seaway to North America. The alternate route to North America via island hopping across the deep Panthalassa Ocean is not supported by current taxonomic evidence. All Swadelina species will be evaluated in this contribution for potential international correlation and to more precisely date dispersal events. A new phylogenetic hypothesis that accounts for this paleobiogeography will be proposed.