This frill served a number of functions, including:
Protection: The frill provided the protoceratops with a degree of protection against predators. Although the frill was not as large or elaborate as that of some other ceratopsian dinosaurs, such as the triceratops, it could still be used to deflect blows from predators, or to shield the protoceratops' neck and head.
Display: The frill also played a role in display, both for courtship and territorial purposes. The protoceratops could flare its frill to make itself appear larger and more intimidating, or to attract a mate.
Sensing: Additionally, some scientists believe that the frill may have been used as a sensory organ, helping the protoceratops to detect changes in its environment, such as the approach of predators or potential food sources.
Despite the protection offered by its frill and other adaptations, the protoceratops was still preyed upon by other dinosaurs, including the velociraptor and the tarbosaurus. However, its defenses allowed it to survive for millions of years and to become one of the most common and successful dinosaurs of the late Cretaceous period.