Yet more reflections on agnathan-gnathostome relationships

Evidence for two competing theories of relationships between Recent agnathans (hagfishes and lampreys) and gnathostomes is reviewed. The hypothesis that lampreys and gnathostomes are sister-groups is favored. The more obvious structures (fins, gill chambers, skeleton) seen in fossil agnathans are discussed and conclusions about their distribution are used in an attempt to include the fossil groups within a classification of Recent craniates. It is concluded that heterostracans are the sister-group of lampreys + gnathostomes; that anaspids are the sister-group of lampreys; and that galeaspids are the sister-group of osteostracans + gnathostomes.