Sinophoneus yumenensis and Stenocybus acidentatus are the only dinocephalians from China, and the latter taxon has been proposed to be a junior synonym of the former. Here I confirm this synonymy on the grounds that the differences between the two putative taxa are due to ontogenetic variation. The osteology of Sinophoneus yumenensis is described in detail based on both previously described specimens and several new ones from the same locality. Sinophoneus yumenensis differs from all other anteosaurs in having premaxillary dorsal processes that are separated by relatively long nasal anteromedial processes, and vomers without raised, elongated edges; from all other anteosaurs except Archaeosyodon praeventor in having distinct frontal posterolateral processes, and a wide intertemporal region formed partly by long posterior processes of the postfrontals that approach the posterior edge of the skull roof; and from Archaeosyodon praeventor in having a well-developed midline ridge on skull roof. A revised phylogenetic analysis including the new material recovers Sinophoneus as the most basal known anteosaurid.

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