Rhinoceros beetle

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Pictured is Dynastes hercules, a giant rhinoceros beetle from Central and South America. Male rhinoceros beetles have large horns on their head and thorax that they use as weapons in male-male battles over access to females. The shapes of these horns differ widely among species. Erin McCullough et al. built biomechanical models of the horns of different species, and found that horns perform better at their own style of fighting than they do at the fighting style of other species. These results suggest that selection for improved performance under different fighting styles played an important role in the diversification of weapon form. Image courtesy of Frantisek Bacovsky.
“Structural adaptations to diverse fighting styles in sexually selected weapons,” by Erin L. McCullough, Bret W. Tobalske, and Douglas J. Emlen
10.1073/pnas.1409585111