Antiquity and Evolution of Prosternal Horns in Baridine Weevils (Coleoptera: Curculionidae)

Among weevils of the subfamily Baridinae (548 extant genera and ca. 9,000 species), unique prosternal horns and associated sheaths have evolved independently multiple times. These structures are utilized in a unique form of male-male aggression in which males push, rather than overturn as in most other horned beetles, their competitor. Herein we report the first fossils of male Baridinae exhibiting such prosternal horns. Two males recovered from the middle Eocene Green River Formation in northwestern Colorado serve to provide a minimum age (at ca. 47 million years old) for both the origin of horns and its associated form of male-male combat in Baridinae.