Variation and covariation of the molar crown elements in the genus Ondatra (Rodentia, Arvicolinae)

Variation and covariation of the molar crown elements of prismatic dentition in the genus Ondatra (Mammalia: Rodentia: Arvicolinae) was studied numerically by means of geometric morphometric and cluster analyses. 31 elements were identified in total, their shapes were described by semilandmarks, their covariation patterns were analyzed by cluster analysis of vectorized Procrustes distance matrices with bootstrap estimations of cluster supports. Within-tooth comparisons recognize the modules that combine crown elements corresponding to the opposing pairs of cusps characteristic of generalized cricetine dentition. Results of comparison of crown elements within each toothrow indicate that integration effect, uniting homologous elements in adjacent teeth into dispersed modules, may be stronger than that uniting opposing elements in the same teeth. Comparison of crown elements of upper and lower toothrows reveals covariation of anterior part of lower M1 and posterior part of upper M3, which underwent coherent complication in the arvicoline evolution. It is concluded that the approach, based on combination of elementaristic GM-description of dental crowns and cluster analysis of covariations of their elements, may become an important tool for exploration of integration patterns of specialized dentition in herbivorous mammals.