This chapter describes the paleobiology of Santacrucian cingulates (armadillosand glyptodonts). At least five genera of armadillos and four genera ofglyptodonts were sympatric in the Santa Cruz Formation. Body masses werecalculated based on a variety of scaling models, allometric equations, multipleregressions, and geometric similarity. The locomotor habits were inferred fromindices previously modeled in living dasypodids, using morphogeometric analysesand the application of a strength indicator. Feeding habits were inferred fromjaw biomechanics, and the shape, arrangement, and wear patterns on teeth, andfrom ecomorphological analyses. All armadillos fall in the range of medium-sizedliving armadillos, and all glyptodonts are larger than any living armadillo,slightly greater than 100 kg, but are smaller than MiddleMiocene–Pleistocene glyptodonts. All Santacrucian armadillos were gooddiggers but none reached the degree of fossoriality found in some specializedliving taxa; all glyptodonts were ambulatory. The variation in the masticatoryapparatus of the armadillos exceeds that in the living species, denoting abroader range of specializations and strong niche partitioning among the fossilspecies. The degree of variation in the masticatory apparatus of glyptodontssuggests differences in the selectivity of feeding and habitat preference. Thetaxonomic richness of armadillos is similar to that recorded today in theChaqueña biogeographic province, supporting the environmentalinterpretation of a mixture of open and relatively closed vegetation inrelatively dry conditions.