Abstract: 【Aim】 The metendosternite of beetle is a kind of endoskeleton that is made of chitin. The base of metendosternite is located on hind coxae with free end in the thorax. As the junction point of muscles in chest movement, metendosternite not only plays an important role in the movement of beetles, but also loads the information of classification and system development. According to the habits, dung beetles have two behavior types: tunnelling and rolling. We can not understand the influences of the two behavior types on the morphology of metendosternites through traditional comparative morphology. This study aims to use quantitative geometric morphology method to explore the relationship between behavior type and the response of metendosternites of dung beetles to selective pressure. 【Methods】 The morphological diversity of 76 species of dung beetles was quantitatively analyzed by two-dimension geometry morphology quantitative analysis. The 3D model of the two representative species of the dung beetles, Copris hispanus and Kheper devotus, was reconstructed using Micro CT and the three-dimension reconstruction, and the morphological differences of the metendosternites between both were compared. 【Results】 The p-values of the Mahalanobis distance and Procrustes distance of metendosternite of the two representative species were all less than 0.0001 through the geometric morphology analysis, indicating that the two dung beetles have significant differences in morphology of the metendosternites. The largest differences are the front section of metendosternites (furcal arm and median process) through the comparison of the 3D model of the two dung beetles. The furcal arms (F.A.) of C. hispanus are long and thin, the median process (M.P.) is wide, and the dorsal longitudinal flange (D.L.F.) is narrow and underdeveloped. The furcal arms of K. devotus are flat and broad, the basal parts of the furcal arms are very wide, the median process is small, and the dorsal longitudinal flange is very derdeveloped and looks like a fins. 【Conclusion】 The behavior type of tunnelling or rolling has a significant impact on the morphology of the metendosternites of dung beetles. The morphology of metendosternites has significant correlation with selective pressure of the two behavior types, and this morphology has a close relation with the movement of the muscles that adhere to the metendosternites involved in. This study provides a good example to explore the relationship between morphology and function in insects.  

Key words: Dung beetle, metendosternite, geometric morphology, three-dimension computer reconstruction, evolution, selective pressure