What specific configuration defined the frill ornamentation on Xenoceratops parietal bones?

Two thick knobs near the midline, each next to a single, long, backward-projecting spike

The unique frill structure of *Xenoceratops* is defined by specific bony outgrowths on the parietal bones. This morphology consists of two relatively thick knobs situated close to the midline. Immediately adjacent to each of these central knobs, there was one long, flattened spike that projected distinctly backward and outward (laterally). Additionally, the front corners of the parietal featured a distinctively triangular knob. This arrangement contrasts sharply with later forms which might have many spikes or hooks, positioning *Xenoceratops* as an earlier stage in centrosaurine frill evolution.