Final answer:
Pachycephalosaurids likely used their enlarged heads for intra-specific combat and display.
Step-by-step explanation:
The enlarged heads of pachycephalosaurids were probably used primarily for intra-specific combat and display.
Pachycephalosaurids were a group of dinosaur species characterized by their thick, dome-shaped skulls.
These skulls were built to withstand and absorb the impact of head-butting, which was likely used as a means of competition between individuals for mates or territory.