How does the bony stay beneath the eye distinguish scorpaeniform fishes from other bony fishes?

The presence of a bony stay beneath the eye is the primary diagnostic feature that distinguishes scorpaeniform fishes from other bony fishes.1

This structure is formed by the union of the second infraorbital bone with the preopercular bone, creating a rigid bar or stay that runs across the cheek. While this feature may be small and inconspicuous in some primitive species or secondarily reduced in specialized forms, it is often externally prominent in many scorpaeniforms, sometimes bearing spines or fusing with other cranial bones to provide hard armor. Because of this characteristic, these animals are frequently referred to as "mail-cheeked" fishes.123