What animals have keratin on their body?

Many animals have keratin in various forms on their bodies, including mammals, reptiles, and birds. For instance, mammals like elephants have keratin in their tusks and nails, while rhinoceroses have thick skin made of keratin. Birds have feathers composed of keratin, and reptiles like snakes and lizards have scales made of this durable protein. Keratin serves various functions, including protection, insulation, and structural support.