The relationships of antiarchs (Devonian placoderm fishes) - evidence supporting placoderm monophyly.

Abstract

A recent analysis of the vascularization of the pectoral fin in antiarchs indicated that they resembled jawless osteostracans rather than other jawed vertebrates, thereby challenging the monophyly of the class Placodermi. Examination of the evidence proposed to support this new hypothesis shows misinterpretation of well-established morphology in a range of antiarchs, with incorrect homologies being applied to conclude that the subclavian artery and vein originated in the back of the branchial chamber. The interpretation is rejected and evidence is summarized showing that pectoral fin vascularization in antiarchs conforms with that of other jawed fishes. The position of the antiarchs as a major subgroup of the placoderm fishes is confirmed, with four antiarch characters (external endolymphatic openings; palatoquadrate-suborbital plate complex; Meckel's cartilage-infragnathal connection; extensive postorbital endocranial processes) providing additional support for placoderm monophyly.