Abstract

Kiangyousteus yohii Liu, 1955, is a eubrachythoracid arthrodire fish (Placodermi) from the Middle Devonian Guanwu Formation of south‐western China. Although Kiangyousteus was the first arthrodire described in China, its phylogenetic position within the Eubrachythoraci remained uncertain because of a lack of diagnostic data in previous studies. A detailed redescription of this taxon reveals similarities to Dunkleosteus terrelli in the possession of transverse articular facets on the parasphenoid and the lack of adsymphyseal denticles on the anterior supragnathal. Our phylogenetic analysis assigned K. yohii to the family Dunkleosteidae, which includes Eastmanosteus calliaspis, Eastmanosteus pustulosus, Golshanichthys asiatica, Heterostius ingens, Xiangshuiosteus wui, and Dunkleosteus. The analysis also yielded several new scenarios on eubrachythoracid interrelationships, notably the sister‐group relationship between Coccosteomorphi and Aspinothoraci, the polyphyly of the referred species of Eastmanosteus, and the assignment of Heterostius and Xiangshuiosteus within the Dunkleosteoidea.