Phylogenetic relationships of North American cyprinids and assessment of homology of the open posterior myodome

Phylogenetic analyses based on complete nucleotide sequences of mitochondri al 12S and 16S rRNA genes support the existence of three major clades withi n the North American phoxinins (Teleostei: Cyprinidae): the western clade, the creek chub clade and the open posterior myodome (OPM) clade. Analyses i ndicated strong support for the OPM clade including, among others, Mylochei lus, Pogonichthys, Tiaroga, and Rhinichthys. These latter taxa do not exhib it an OPM and previously have not been hypothesized to be related to member s of the OPM clade. Parsimony analysis resolved relationships among basal m embers of the OPM clade and provided an opportunity to address homology of the OPM. Two hypotheses of homology of the OPM were included in analyses, w ith DNA sequence data allowing investigation of homology and evolution of t he OPM. The OPM is best treated as a complex character exhibiting phylogene tic and ontogenetic variation. Previous attempts to simplify coding of the character do not result in hypotheses of homology that are congruent with p hylogenetic hypotheses based on DNA sequence data.