The probable diets of members of the extinct ruminant family Dromomerycidae were determined via an assessment of gross anatomical correlates of feeding strategy, mesowear analysis, and microscopic scar topography of enamel surfaces of cheek teeth. Discriminant models derived from 108 extant ruminants of known diet were applied to fossil taxa to ascertain probable trophic habits in dromomerycids. Microwear and mesowear analyses of molar tooth wear supplemented this gross skull and tooth morphological assessment as a means of providing more direct and independent sources of evidence for the nature and potential shifts in diet within dromomerycid lineages. In general, estimations of diets obtained from the study of gross morphology correlated well with those obtained from wear patterns. However, this was not always the case, suggesting that independent means of dietary analysis are critical when attempting to reconstruct paleodiets. In addition, hypsodonty (relative molar crown height) proved to be problematic as a variable in determining the diet of these extinct taxa. Information obtained from gross morphology, microwear, and mesowear support the hypothesis that later species of the Dromomerycidae within the tribe Cranioceratini had a shift in diet toward coarser food materials as a response to a trend toward increasing aridity and a shift in vegetational structure in the late Miocene–early Pliocene of North America.