Final answer:
Frill spikes of Ceratopsids like Styracosaurus are made of bone, covered in keratin, which serves as a protective layer, and are comparable to the horns of modern-day Bovids.
Step-by-step explanation:
What distinguishes the frill spikes of Ceratopsids, like Styracosaurus, from other structures is that they are made of bone. As for the subfamily of Ceratopsids known for having long spikes or prongs on the frill, it is the Centrosaurinae. The role of keratin in the context of Ceratopsid frill spikes serves as a protective covering. Among the mentioned Ceratopsids, Styracosaurus is known for its distinctive frill spikes. The modern-day species that share a similar keratin structure with Ceratopsid frill spikes are Bovids, like cows and goats. The frill spikes of Ceratopsids can be considered horns because they are sheathed in keratin.