Illustration of the horned Late Cretaceous (101-66 million years ago) theropod dinosaur Carnotaurus sastrei, interpreting it as growing a much longer (but still plausible) keratinous sheath over its brow horn cores than is usually reconstructed. Dinosaurs grew a substantial amount of keratin on bony horn cores, making horns look larger and more elaborate in life than the horn core alone would suggest. This makes sense especially for horns that are used for display purposes.