The eutatines are a group of fossil armadillos traditionally regarded as herbivorous due to the particular morphology of the skull and teeth. Nevertheless, they have never been the subject of a detailed morpho-functional analysis. The masticatory apparatus of Eutatus (late Pliocene-early Holocene) is analyzed and compared with other eutatines (Proeutatus and Stenotatus from the Miocene, and Doellotatus and Ringueletia from the Pliocene) and with living armadillos (Euphractus and Dasypus). The masticatory muscles were reconstructed from origin and insertion scars; the occlusal pattern and mandibular movements were determined through the study of the craniomandibular joint, the shape and arrangement of the teeth and the symphysis, and the moment arms of the lines of action of the masseter and temporalis muscles were estimated. Skull and mandible shapes were compared using the Procrustean method Resistant-Fit Theta-Rho-Analysis (RFTRA). The analysis of the masticatory apparatus of the eutatines allows us to state that Eutatus and Proeutatus exhibit the most specialized morphology known for an herbivore with an armadillo-like skull pattern. Additionally, we can identify a morphological group from the Miocene Stenotatus to the Pleistocene Eutatus, including the Pliocene Doellotatus and Ringueletia as intermediate stages of a morphological line; Proeutatus deviates from this pattern. This morphological separation may reflect an early dichotomy within the well-defined clade of eutatines.