The development and evolution of the rodent mandible have been studied in depth in recent years. The mandible is a complex structure because it consists of six morphogenetic components formed by different condensations of mesenchymal cells. Using recent techniques for the geometric analysis of shape, we have combined developmental information with a powerful quantification of shape variation and an independent estimate of phylogeny (molecular data) to assess the evolutionary patterns of shape change in mandibles of the rodent genus Trinomys. In general, the major trends in shape variation did not agree with the expected phylogenetic pattern. However, for small-scale morphological differences, one species (T. yonenagae) was responsible for the lack of association between morphology and molecular divergence. This species is genetically similar to but morphologically different from other Trinomys. The coronoid process was considered to be the most conservative morphogenetic component in the mandible.434332338