Caviomorphs constitute a monophyletic group, representative of the oldest rodentradiation in South America. Since the Oligocene they have contributedimportantly to the fossil communities of South American mammals. Today,caviomorphs display a diverse array of locomotor and feeding behaviors,occupying a wide range of habitats in which they consume a variety of fooditems. In this contribution, we analyze species of Santacrucian caviomorphs froma morphofunctional perspective in the context of extant caviomorph behavioraldiversity, in order to evaluate their paleobiology and its paleoenvironmentalsignificance. Body masses based on Santacrucian specimens were estimated byapplying published equations. Reconstructions were made of areas of origin andinsertion of the main masticatory muscles following the muscular patternobserved in living caviomorphs. On this basis, functional analyses of themasticatory apparatus were performed. Major postcranial features in extantcaviomorphs identified as functionally associated with different locomotorhabits were used as a model to evaluate the functional significance of thepostcranial features in Santacrucian species. Santacrucian caviomorphs examinedshow the range of body mass from small- to relatively large-sized livingcaviomorphs. The porcupine Steiromysduplicatus and the dasyproctid Neoreomysaustralis present features that indicate a diet of harder andmore abrasive food items than those consumed by living Neotropicalphylogenetically related species. Features of the masticatory apparatus of theeocardiid Eocardia fissa are compatible witha wide feeding behavior, including abrasive food. Steiromys duplicatus was a semi-arboreal form, which did notachieve the degree of specialization that is seen in the Neotropical extantCoendou. Eocardiafissa was a cursorial agile rodent, similar to living Pediolagus salinicola. Neoreomys australis was a cursorial species, more similar toliving Agouti paca than to Dasyprocta species. Santacrucian caviomorphs couldhave lived in an environment like the Cerrado biome, showing differentialutilization of food resources and locomotor behaviors.