of Protopteraspididae as sister taxa. Phylogeny Based on the work of Mikko Haaramo. See also Astraspidida Thelodonti Galeaspida Osteostraci Lepidaspis References External links tolweb.org pwrmark.biology.ualberta.ca geol.lsu.edu Vertebrate subclasses de:Pteraspidomorphi#Heterostraci