Phylogenetic relationships of the Middle Ordovician trepostome bryozoans Sonninopora and Bimuropora

Bimuropora dendroidea, previously assigned to other genera, is described from Tennessee and B. winchelli is reported from Nevada. The occurrence of B. winchelli in Nevada extends the geographic range of the Middle Ordovician trepostome genus Bimuropora in North America. These two species share many derived characteristics with the halloporids, including a similar growth pattern and fluted zooecial walls in the endozone. This strengthens the hypothesis that the bimuroporids are a sister group to the halloporids. Sonninopora, a monospecific genus, contains these same features, and because of the presence of acanthostyles it is removed from the family Halloporidae and assigned to the family Bimuroporidae.