Tylocephalonyx (Greek: "knob" (tylos), "head" (kephalos), "claw/hoof" (onyx)[2]) is an extinct chalicothere from the Miocene of North America.

Tylocephalonyx specimens are notable for a dome-shaped skull, a feature found in some other schizotheriine chalicotheres but most developed in this genus.

Adequate fossil material is lacking to tell whether both sexes had domed heads, but sexual dimorphism was common in the group.

Such contests require special cranial adaptations to protect the brain and cervical spine, not shown in chalicotheres.

The dome of Tylocephalonyx may have been used for visual display or in butting or head-to-body battering contests.