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

Description

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. Tylocephalonyx may have used its "dome" in the same way as the pachycephalosaurs, though there is no clear evidence to link either pachycephalosaurs nor Tylocephalonyx to using their domes to crash together in high-impact head-to-head contests, as in modern bighorn sheep. 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.

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