Phylogenetic relationships of the cyathaspidids (Heterostraci)

The present analysis investigates for the first time the phylogenetic relationships of the cyathaspidid heterostracans by the principle of global parsimony on the basis of 36 species and 1 outgroup taxon. In this study, which assumes cyathaspidid monophyly, states for 61 characters were compiled and analysed using maximum parsimony methods, resulting in nine shortest trees of 122 steps each. The strict consensus tree shows a high degree of homoplasy and challenges previous classification schemes. The consensus topology supports previous arguments that the tolypelepids with their characteristic scale-like ornament occupy a basal position among the cyathaspidids.