Redescription of a Middle Devonian placoderm from Manitoba and comments on the polyphyly of <i>Eastmanosteus</i> (Arthrodira: Eubrachythoraci)

Arthrodires are the most common and diverse placoderms, an extinct group of early jawed vertebrates. Although commonly found, numerous taxa remain poorly known, thereby complicating the establishment of their taxonomic affinities. An excellent example of this is the genus <i>Eastmanosteus</i>: originally assigned to the wastebasket <i>Dinichthys</i>, it now comprises several species whose description was based on highly incomplete material. Thus, it has been suggested that <i>Eastmanosteus</i>, in turn, has become a wastebasket taxon. Here we redescribe <i>Elmosteus lundarensis</i> gen. et comb. nov., previously assigned to <i>Eastmanosteus</i>. An updated description is provided based on new material recovered from the Elm Point Formation, Middle Devonian (Eifelian–Givetian), near Lake Manitoba, MB, Canada, including gnathal elements, the median dorsal plate, and a ventral view of the skull roof. Parsimony and Bayesian phylogenetic analyses were performed, in which the more complete species of <i>Eastmanosteus</i> were included. <i>Elmosteus</i> is recovered as a basal dunkleosteid and all analyses support the polyphyly of <i>Eastmanosteus</i>. A brief discussion about intraspecific variation in <i>El. lundarensis</i> is also provided. Revisions of taxa described long ago, such as <i>Eastmanosteus</i>, using modern techniques like computational phylogenetics is essential for further improved taxonomy. This will lead to a better definition of relationships within placoderms and a better understanding of their diversity, and in turn help us trace the early evolutionary steps of vertebrate traits among stem gnathostomes. https://zoobank.org/urn:lsid:zoobank.org:pub:C52D3188-ED7F-4C7B-83C6-4A78C88B1591