the large predatory dinosaurs of the time. Although pitting, holes, lesions, and other damage on ceratopsid skulls are often attributed to horn damage in combat, a 2006 study found no evidence for horn thrust injuries causing these forms of damage (for example, there is no evidence of infection or healing). Instead, non-pathological bone resorption, or unknown bone diseases, are suggested as causes. However, a newer study compared incidence rates of skull lesions in Triceratops and Centrosaurus and showed that these were consistent with Triceratops using its horns in combat and the frill being adapted as a protective structure, while lower pathology rates in Centrosaurus may indicate visual rather than physical use of cranial ornamentation, or a form of combat focused on the body rather than the head; as Centrosaurus was more closely related to Styracosaurus and both genera had long nasal horns, the results for this genus would be more applicable for Styracosaurus. The researchers also concluded that the damage found on the specimens in the study was often too localized to be caused by bone disease. The large frill on Styracosaurus and related genera also may have helped to increase body area to regulate body temperature, like the ears of the modern elephant. A similar theory has been proposed regarding the plates of Stegosaurus, although this use alone would not account for the bizarre and extravagant variation seen in different members of the Ceratopsidae. This observation is highly suggestive of what is now believed to be the primary function, display. The theory of frill use in sexual display was first proposed in 1961 by Davitashvili. This theory has gained increasing acceptance. Evidence that visual display was important, either in courtship or in other social behavior, can be seen in the fact that horned dinosaurs differ markedly in their adornments, making each species highly distinctive. Also, modern living creatures with such displays of horns and adornments use them in similar behavior. The use of the exaggerated structures in dinosaurs as species identification has been questioned, as no such function exists in vast majority of modern species of tetrapods (terrestrial vertebrates). A skull discovered in 2015 from a Styracosaurus indicates that individual variation was likely commonplace in the genus. The asymmetrical nature of the horns in the specimen has been compared to deer, which often have asymmetrical antlers in various individuals. The study carried out may also indicate that the genus