Osteohistology of Antilocaprid Horncores

Cranial bony projections (“headgear”) have diverse forms and functions, such as defense, species recognition, and mate selection. Most commonly, cranial appendages are associated with the mammalian order Artiodactyla. Broadly, all artiodactyl headgear––antlers, horns, ossicones, pronghorns––are osseous protrusions of the frontal or parietal bone with an integumentary covering, although there is taxonomic developmental and histological disparity. This discrepancy is under-investigated, yet its exploration could inform metabolic demands and sociality during life, and diagnostic features in the fossil record. While a plethora of literature addresses the osteohistology of ornamentation in cervids, bovids, and giraffids, current literature on antilocaprid horns is restricted to keratin sheath growth and conflicting descriptions aligning development with the disparate patterns of both cervids and bovids. Furthering confusion about antilocaprid horncore development and evolution are recent genetic sequencing reports that show a closer relationship between Antilocapridae and Giraffidae. Despite their wide availability as specimens, no modern osteohistological examinations of antilocaprid horncores have been completed. This study provides a novel osteohistological description of antilocaprid horncores in order to build a comparative understanding of how these structures develop. Preliminary data of an adult male and female reveal the majority of cortical area in transverse section is secondarily remodeled trabecular cortex, indicating the horncore undergoes frequent remodeling. Deep to the periosteal surface, the thin outer cortex of compact tissue is highly vascularized fibrolamellar bone, revealing continued growth of the horncores beyond skeletal maturity. A greater understanding of horncore development is fundamental to further research into the evolution and function of headgear in Antilocapridae, such as social behaviors and thermoregulation.