Classification and Phylogeny of Fossil and Recent Fishes

A classification of the 26 taxa of fossil and recent fishes is presented together with thoughts regarding their phylogenetic relationships. In addition to myllokunmingiids, dated as middle Cambrian, cyclostomes (including present-day myxinids and lampreys) are also recognized here as having Cambrian origins, based on their divergence time estimated from a molecular analysis. Ostracoderms (agnathans characterized by exoskeletons), a paraphyletic grouping including pteraspidomorphs, anaspids, thelodonts, and cephalaspidomorphs, were dominant in the Palaeozoic Era; pteraspidomorphs, comprising arandaspids, astraspids, and Eriptychius in the Ordovician and heterostracans in the Siluro-Devonian Periods; anaspids comprising birkenids, Jamoytius, and euphaneropids in Siluro-Devonian Periods, therodonts in Ordovician and Siluro-Devonian Periods, and cepharaspidomorphs, including osteostracans, galeaspids, and pituriaspids, also being Siluro-Devonian ostracoderms. Osteostracans and gnathostomes share the perichondral bone derived from other ostracoderms. Gnathostomes (jawed fishes) consist of placoderms, maxillate placoderms, Janusiscus-Ramirosuarezia, osteichthyans, and chondrichthyans. Placoderms diversified remarkably during the Devonian, and are located here at the base of gnathostomes, due to some ostracoderm similarities; maxillate placoderms with dermal premaxillary, maxillary, and dentary-like osteichthyans in the Silurian. Janusiscus-Ramirosuarezia have no otico-occipital fissure. Osteichthyans and chondrichthyans share dental lamina and otico-occipital fissure that differ from placodermi. Osteichthyans include ancestral stem osteichthyans in the Upper Silurian and Middle Devonian which were divided into actinopterygians and sarcopterygians in the Middle Devonian. Chondrichthyans include Ordovician chondrichthyan-like scales, ancestral stem chondrichthyans, acanthodians, and chondrichthyan crown group. Stem chondrichthyans and acanthodians (previously all combined under acanthodians) are now separated on the basis of scale microstructure from each other, and are differentiated from the chondrichthyan crown group, including pucapampellids, holocephalans, and elasmobranchs. Only cyclostomes, actinopterygians, sarcopterygians, holocephalans, and elasmobranchs are now represented among recent fishes.