Keith Philips and I used a phylogenetic tree depicting the branching relationships among dung beetle species to test for an association between evolutionary gains or losses of male horns and the tunneling versus rolling behavior of each species. We found that tunneling behavior strongly predicted the evolution of horns, and when species switched from tunneling to ball-rolling behavior, they subsequently lost their male horns.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 713