>>42880236In all animals. Nails, hair, feathers, horns, hooves, etc. All keratin in all animals. Teeth are a separate thing, but only antlers are actual bone growing out of an animal. Because of this, antlers are covered in skin while they grow, which peels off once the antler has finished growing.
Unlike horns, antlers don't grow continuously, but are shed at the end of each cycle and regrown.
